Abrupt millennial scale climate variations during MIS 7-6 recorded in NISA stalagmites
1Department of Earth Sciences, ETH Zürich, Switzerland; 2Institute of Global Environmental Change, Xi’an Jiaotong University, China; 3Department of Earth Sciences, University of Minnesota, USA
Stalagmites from coastal caves of the North Iberian Speleothem Archive (NISA) record instabilities of northern hemisphere ice sheets impacting the Atlantic Meridional Overturning Circulation (AMOC) resulting in abrupt climate variations in Europe. The oxygen (δ18ONISA) and carbon (δ13CNISA) isotope proxies indicate simultaneous freshening and cold events respectively. Here we present a continuous high-resolution record (splice of 3 stalagmites) spanning 215-140 kyr BP. During MIS 7 interglacial and the Penultimate Glacial (MIS 6) millennial scale climate oscillations are recorded in NISA stalagmites. A larger and dynamic European Ice Sheet during the Penultimate Glacial might have had high impact on AMOC variations due to the proximity of freshwater addition to deep water formation regions in the eastern North Atlantic. Marine proxies from the North Atlantic and Mediterranean are well in line with our NISA record. We evaluate the duration and intensity of such millennial events in different time windows. Furthermore, the global impact of such short and abrupt centennial to millennial scale events are investigated. For example, simultaneous oscillations in the intensity of the South American Summer Monsoon (SASM) are observed and ice core records from Antarctica suggest the activation of the bipolar see-saw affecting the interhemispheric heat transport with restricted impact on the global carbon cycle.
Reconstruction of wildfire occurrence using levoglucosan and lignin biomarkers from Siberian stalagmites.
1Department of Geography and Environmental Sciences, Northumbria University, United Kingdom; 2Department Chemie, Johannes Gutenberg-Universität Mainz, Duesbergweg 10-14, 55128 Mainz, Germany; 3The University of Western Australia, Perth, WA 6009, Australia; 4Alfred Wegener Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Section Marine BioGeoSciences, 27570 Bremerhaven, Germany; 5Geological Survey of Israel, 32 Yeshayahu Leibowitz Street, 9692100 Jerusalem, Israel; 6Speleoclub Arabika, St. Mamina-Sibiryaka 6a, 664058 Irkutsk, Russia; 7Department of Earth Sciences, University of Oxford, South Parks Road, OX1 3AN Oxford, UK; 8Department of Chemistry, Biochemistry and Pharmaceutical Sciences & Oeschger Centre for Climate Change Research, University of Bern. Freiestrasse 3, 3012 Bern, Switzerland
Recent accelerating global temperature rise increases the likelihood and susceptibility of the Siberian taiga to more frequent and extreme wildfires  . This leads to enhanced permafrost thaw and subsequent greenhouse gas emissions, in a positive feedback loop . Various studies have examined these paleofires in Siberia on limited, modern timescales  , but long-term reconstructions of wildfire occurrences are scarce . This study reconstructs and compares wildfire occurrence during the past ca. 400 ka using stalagmites from southern Siberia. We provide a new means for assessing Siberian wildfires during interglacial periods and the first long-term southern Siberian wildfire record.
Three stalagmites from Botovskaya Cave (55˚17’59”N, 105˚19’46”E) have been U/Th-dated at the Oxford Geochronology Laboratory [4,5]. These speleothem samples were collected deep inside the poorly ventilated cave, which is overlain by 40-130 m of sandstone covered by a thin soil and boreal taiga forest. Drip sites are active year-round, and cave air temperature is stable at ca. 1.3 ± 0.5 °C. Wildfires sporadically occur above the cave.
We use levoglucosan and lignin extracted from speleothems as tracers for wildfire activity and vegetation composition above the cave respectively. Levoglucosan is an anhydrous monosaccharide solely produced by the combustion of cellulose, and thus an ideal proxy for wildfires. Lignin is a biopolymer found in all terrestrial plants. After digestion, the ratio of different monomeric units to one another can inform on relative changes between gymnosperm vs. angiosperm and woody vs. non-woody plant communities. Using these proxies we can decipher both wildfire recurrence and changes in vegetation (e.g., from pine forest to peatbogs or grassland).
We took subsamples between 300 and 1000 mg and compare fluctuations of the levoglucosan fire signal to variance of lignin monomers and corresponding vegetation composition. The required sample size (1 g) and the low observed speleothem growth rates of ca. 4-8 µm/a mean that we can only achieve multi-centennial resolution for interglacial periods. To gain complementary insights into environmental conditions we combine the biomarker information with stable oxygen and carbon isotopes and element concentrations.
Hydroclimate Variability of Northeast Mexico during the Eemian Interglacial (128 kya)
1University of California, Irvine, United States of America; 2Massachusetts Institute of Technology, United States of America; 3Universidad Nacional Autónoma de México, Mexico; 4Universidad Autónoma de San Luis Potosí, Mexico
Current global climate models project that drought events in Mexico will increase in both frequency and intensity by the end of the 21st century. However, these models are still highly uncertain in their ability to predict changes in rainfall patterns at the regional to local scales, and some models do not agree on the sign of projected rainfall change. This is in part due to a lack of terrestrial paleoclimate records that provide information on how rainfall patterns respond to warmer climate conditions. This project focuses on developing the first terrestrial record of precipitation in Mexico during the Last Interglacial Period (LIG; 128,000 years ago). These results from a previous warm period will provide a critical analogue for understanding potential rainfall change under future anthropogenic warming. Preliminary field work at Cueva de la Puente (CP) shows that this cave is suitable for paleoclimate reconstruction, where δ18Ocalcite can be used as a proxy for paleo rainfall amount. Stalagmite CP-1 was collected in 2017 and is characterized by dense columnar calcite fabric with high U concentration (~1 ppm). Preliminary U-Th dating conducted at the Massachusetts Institute of Technology (MIT) indicates that it formed from ~48 to 128 kyrs B.P., but with two significant growth hiatuses. Here, we focus on results from a continuous 22.7 cm section of CP-1 that formed during the LIG, with dates ranging from 123,043 yrs (754 yrs) to 128,150 yrs (920 yrs), respectively. The LIG section of CP-1 was microsampled at 250 μm resolution and powders were analyzed for stable isotope and trace element composition, yielding a sub-decadal resolution record. In this presentation, we will present our initial multi-proxy results and discuss decadal to millennial scale hydroclimate variability in NE Mexico during the LIG.
Timing of Dansgaard-Oeschger events in Central Europe based on three precisely dated speleothems from Bleßberg Cave, Germany
1Institute for Geosciences, Johannes Gutenberg University, Mainz, Germany; 2Max Planck Institute for Chemistry, Mainz, Germany; 3German Research Centre for Geosciences, Potsdam, Germany; 4Department of Geography and Environmental Sciences, Northumbria University, Newcastle upon Tyne, UK; 5Potsdam Institute for Climate Impact Research, Potsdam, Germany
The last glacial period and especially Marine Isotope stage 3 (MIS 3, ca. 57 - 27 ka) was characterized by various climate oscillations (i.e., rapid increases in temperature, followed by a gradual cooling, the Dansgaard-Oeschger (D/O) events), which were first discovered in Greenland ice cores. Although their causes are still not fully understood, clear evidence for their supra-regional character was found in various climate records around the globe. However, European speleothem samples, which grew during MIS 3, are limited and mainly restricted to alpine regions, where glacier meltwater enabled speleothem growth, and to south/south-western parts of Europe characterised by a generally warmer climate. This led to the opinion that it was too cold and/or too dry in central Europe for speleothem growth. Here we present three speleothem (flowstone) records from Bleßberg Cave, Germany, which grew during MIS 3.
All flowstones show episodical growth patterns with distinctive, thin growth phases. Potential contamination deriving form detrital material deposited during hiatuses between individual growth phases, open-system behaviour around the hiatuses and the limited thickness of the growth layers are the biggest challenges during sampling for 230Th/U dating. By combination of different sampling techniques (i.e., laser ablation and micro-milling) in addition to the common approach of handheld drilling and due to the relatively high 238U concentration of the samples (approx. 0.4 - 1 µg/g), we were able to date even the thinnest growth layers (< 2 mm) of the Bleßberg flowstones with a very high precision (i.e., with 2σ-age uncertainties of a few hundred years or even lower).
The timing of the growth phases of the Bleßberg flowstones correlates with several D/O events recorded in the Greenland ice cores. This proves that at least some phases of MIS 3 had favourable climate conditions for speleothem growth in Central Europe. In addition, the analysis of the stable oxygen and carbon isotopes (δ18O and δ13C) for all three flowstones revealed several D/O events, which have not been recorded in any other speleothem from central Europe so far. This will enhance our understanding of climate variability during MIS 3 and specific D/O events in central Europe.
Using trace elements to characterize subaqueous calcite deposits in Devils Hole (Nevada)
1Institute of Geology, University of Innsbruck, Innrain 52, 6020 Innsbruck, Austria; 2Ca‘ Foscari University of Venice, Department of Environmental Sciences, Informatics and Statistics, Venice, Italy; 3College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, 101 SW 26th Street, Corvallis, Oregon 97330; 4Department of Earth Sciences, University of Minnesota, 116 Church St. SE, Minneapolis, Minnesota 55455, USA
Subaqueous calcite deposits from Devils Hole (Nevada, USA) have been used to date groundwater oscillations on orbital and multi-millennial timescales (Wendt et al., 2018). The record is based on two types of calcite: 1) slow growing (1 mm/ka), dense mammillary calcite which forms under water and can be reliably dated with U-series techniques; 2) porous and undatable folia which forms directly at the water surface.
In order to date short-term (millennia and shorter) oscillations in the last glacial period, layers less than few mm thin need to be clearly identified prior to analysis. In general, the boundary between mammillary calcite and folia is not sharp, making it difficult to assess whether an individual layer can be reliably dated. In an effort to identify suitable layers, we characterized the two types of calcite by optical petrography, stable isotopes (δ13C and δ18O) and trace elements (Mg, Sr, Ba, U).
Preliminary results show a significant variability in trace-element concentrations in folia, while mammillary calcite has a characteristically uniform concentration of most elements. At transitions from folia to mammillary calcite, elongated crystals which are distinct from mammillary calcite (compact fabric, comprising composite columnar crystals, each being a “bundle” of multiple rod-shaped crystallites) and folia (small, slightly elongated to mosaic-like crystals) were found as an additional, third type of calcite. The Mg/Ca ratio in mammillary calcite and the transition zone is higher by an order of magnitude relative to folia. Ba/Ca and Sr/Ca are elevated in the transition zone relative to mammillary calcite and folia by an order of magnitude.
Where thin calcite layers are similar to these transition zones, they can be clearly distinguished from folia and may inform us about the timing of short-term climate oscillations.
Wendt, K. A., Dublyansky, Y. V., Moseley, G. E., Edwards, R. L., Cheng, H. & Spötl, C., 2018, Moisture availability in the southwest United States over the last three glacial-interglacial cycles Science Advances, 4, https://doi.org/10.1126/sciadv.aau1375.
A paleoprecipitation and paleotemperature record of the Last Interglacial in the southeastern Alps
1University of Innsbruck, Austria; 2Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Water Resources and Drinking Water, Überlandstrasse 133, 8600 Dübendorf, Switzerland; 3ETH Zurich, Department of Environmental System Sciences, Institute of Biogeochemistry and Pollutant Dynamics, Universitätstrasse 16, 8092 Zürich, Switzerland; 4Department of Earth Sciences, University of Minnesota, Minneapolis, MN, USA; 5Institute of Global Environmental Change, Xi’an Jiaotong University, Xi’an 710054, China
<p>The Last Interglacial (LIG, ~130–116 ka) was one of the warmest interglacials of the past 800,000 years. It is an important test bed for even warmer conditions than today and provides a unique opportunity to investigate the effect of differently distributed radiative forcing on the hydrological system. The most widely available LIG temperature reconstructions are from marine records, and some climate model simulations show that land masses might have been considerably warmer by about 2° to 5°C, at mid and high northern latitudes (Bakker et al., 2014). In Central Europe, the LIG has been widely studied using pollen preserved in mires and lake sediments and more recently chironomids. While these records document temperatures changes across the LIG, they are poorly constrained chronologically. Speleothems offer superior age control and provide information of past climate, including qualitative and also quantitative records of temperature and precipitation. Here, we present a new, precisely dated fluid-inclusion record based on 7 speleothems that were retrieved from two caves in the SE Alps (Obir and Katerloch) including the use of a δD/T° transfer function and noble gases dissolved in the water inclusions to reconstruct LIG temperatures. We report a temperature change across the Glacial/Interglacial transition of 6.1°± 3.7°C based on noble gas temperatures that is consistent with the 7.1± 3.1 °C shift as suggested by the δD/T° transfer function calculated from fluid inclusion δD values. The δD record from these speleothems exhibits millennial-scale events during the LIG that are not well expressed in the calcite δ<sup>18</sup>O.</p>
Geochemical investigation of periodic red layers trapped in a Bahamas speleothem.
1Department of Geology, University of Innsbruck, Innrain 52, 6020 Innsbruck, Austria.; 2Bahamas Caves Research Foundation, Abaco Island, Bahamas; 3School of Earth and Environmental Sciences, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455, USA.; 4Department of Earth Sciences, Sonneggstrasse 5, 8092 Zürich, Switzerland
Atmospheric dust transport is known to be an important factor in glacial climates, having an effect on radiative transfer, clouds, and the global carbon cycle. In the present environment, soils in the Bahamas are composed primarily of dust that has been transported by westerlies from the Sahara, and here we utilise a unique approach using speleothems to investigate the trans-Atlantic transport of dust in the recent geological past. For many decades, the genesis, age, and geochemistry of speleothems from the Bahamas have been used to improve our understanding of palaeoclimate environments. Here, we present the results of geochemical investigations into a speleothem collected from -25.6 m below sea level in Dan's cave, Abaco Island, Bahamas. The sample has an interesting tripartite structure, beginning and ending with opaque crystalline calcite, but in between it has a middle section containing distinct oscillating red and opaque layers several mm thick. We have attempted to characterise the red layers to establish their origin using micro-X-ray fluorescence, laser ablation inductively coupled plasma mass spectrometry, petrography, and stable isotope analysis. U-Th dating reveals that the speleothem was deposited during Marine Isotope Stages 10 and 8, indicating maximum sea level elevation during those periods. The hiatus during MIS 9 is considered to be sea-level controlled. We hypothesise that the millennial-scale oscillating red-opaque layers, which were deposited during the first half of the MIS 8 glacial, formed during times of increased atmospheric dust transport from the Sahara to the Bahamas. This transatlantic aeolian mineral dust transport is mainly controlled by the African monsoon strength and further the position of the Intertropical Convergence Zone (ITCZ), indicating a weak monsoon and a southerly position of the ITCZ during early MIS 8 that is synchronous with cooler sea surface temperatures (SSTs) in the sub-tropical Atlantic. During the later part of MIS 8, SSTs increased and atmospheric dust transport to the Bahamas declined. Further research on speleothems and cave sediments from the Bahamas could prove to be unique archives for trans-Atlantic dust transport.
The 8.2 ka event in Northern Spain: timing, structure and climatic impact from a multi-proxy speleothem record
1Université Savoie Mont Blanc, France; 2The University of Melbourne, Australia; 3Universidad Complutense, Spain; 4Australian Nuclear Science and Technology Organisation, Australia
The 8.2 ka event is regarded the most prominent climate anomaly of the Holocene. The event is thought to have been triggered by a meltwater release to the North Atlantic that was of sufficient magnitude to disrupt the Atlantic Meridional Overturning Circulation (AMOC). The 8.2 ka event is most clearly captured in the Greenland ice-core records, where it is reported as a cold and dry anomaly lasting ~160 years, from 8.25 ± 0.05 ka BP until 8.09 ± 0.05 ka BP (Thomas et al., 2007). It is also recorded in several archives in the North Atlantic region, however, its interpreted timing, evolution and impacts vary significantly. This inconsistency is commonly attributed to poorly constrained chronologies and/or inadequately resolved time series.
Here we present a high-resolution speleothem record of early Holocene palaeoclimate from El Soplao cave in Northern Spain, a region pertinent to studying the impacts of AMOC perturbations on south-western Europe. We explore the timing and impact of the 8.2 ka event on a decadal scale by coupling speleothem stable carbon and oxygen isotopic ratios, trace element ratios (Mg/Ca and Sr/Ca) and growth rate. The 8.2 ka event is marked as a centennial-scale negative excursion in δ18O, starting at 8.19 ± 0.06 ka BP and lasting until 8.05 ± 0.05 ka BP. Most of the δ18O variability throughout the Holocene part of the record is related to changes in effective recharge, mainly controlled by the rainfall amount. The variability of δ13C, Mg/Ca and growth rate are also related to effective recharge. Yet these proxies display negligible change across the 8.2 ka event compared to the amplitude of the δ18O excursion. Thus, we interpret the excursion in the δ18O as predominantly driven by changes in the isotopic composition of the moisture source, associated with the meltwater release by the drainage of lakes Agassiz and Ojibway.
In comparing the El Soplao record with other well-dated speleothem time series from the region, we find that the 8.2 ka event was synchronous in south-western Europe with an error-weighted mean age for the onset of 8.23 ± 0.03 ka BP and 8.10 ± 0.05 ka BP for the end of the event. Additionally, the event is structurally similar amongst most of these other regional archives, and comparable to the NGRIP ice-core record. According to some of these records, there were increased amounts of rainfall in south-western Europe concomitantly with the δ18O excursion in the Greenland ice cores. In others, including our record, speleothem δ18O only appears to record a modification of the isotopic composition at the moisture source.
Climate variations in southwestern and Central Iran during Marine Isotope Stage 3
1Institute of Geology, University of Innsbruck, Innsbruck, Austria; 2Department of Geology, University of Isfahan, Isfahan, Iran; 3Department of Earth Science, University of Cambridge, Cambridge, United Kingdom
<p>Records of paleoclimate in the Middle East are particularly sparse in comparison with other regions around the world. In order to better resolve how Middle East climate responded to large global climate and environmental changes in the past, we present the first record of Marine Isotope Stage (MIS) 3 from southwestern and central Iran climate constructed using speleothem climate proxies. We analyzed one stalagmite each from a cave on the western side of the Zagros Mountains, ~100 km north of the Persian Gulf, and from arid Central Iran. Average annual precipitation and temperature close to the cave sites are ~350 mm and ~21.6 °C, and ~162 mm and 16.8°C, respectively. Our data yield δ<sup>18</sup>O and δ<sup>13</sup>C records which span a large portion of MIS 3. The timing of significant fluctuations in isotopic values of our record are in broad agreement with North Atlantic Heinrich events and Greenland Daansgard Oeschger (D-O) events, within the respective records’ age uncertainties. The start of growth of the Central Iranian stalagmite coincided with D-O event 12 (~ 46 ky), after the Heinrich (H) 5 cold period. The growth of both Central and SW Iran stalagmites ceased at ~30 ky, corresponding to H3. Stadials and interstadials in Greenland coincide with intervals of less and more negative δ<sup>18</sup>O values in Iranian speleothems, attributed to less and more humid climate in the region, respectively.</p>
<p>The SW Iran stalagmite δ<sup>18</sup>O values are consistently higher than Eastern Mediterranean stalagmite δ<sup>18</sup>O values, while the Central Iran δ<sup>18</sup>O values in the same period are lower than both SW Iran and Eastern Mediterranean δ<sup>18</sup>O values. We investigate changes in moisture sources, moisture trajectories, and/or evaporation effects which may have influenced the offset of the δ<sup>18</sup>O records of the Iranian sites compared to the Eastern Mediterranean stalagmite δ<sup>18</sup>O records.</p>
PERSISTENT SUB-MILLENNIAL-SCALE HYDROCLIMATIC VARIABILITY IN THE SOUTHWEST INDIAN OCEAN OVER THE PAST 13 KA
1Institute of Global Environmental Change, Xi’an Jiaotong University, Xi’an, 710056, China; 2Department of Earth Science, California State University Dominguez Hills, Carson, 90747, USA; 3Institut für Geologie, Universität Innsbruck, Innsbruck, 6020, Austria; 4State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, 710061, China; 5Key Laboratory of Karst Dynamics, MLR, Institute of Karst Geology, CAGS, Guilin, 541004, China
The precipitation over the tropical southwest Indian Ocean (SWIO) is highly variable and sensitive to changes in the tropical Pacific sea surface temperature (SST) and meridional shifts of the southern boundary of the tropical rainfall belt. In our previous study, we reported the speleothem-based reconstruction of the SWIO hydroclimatic variability from Rodrigues Island (19°45′S, 63°23′E) over the past 8 ka years (Li et al, 2020). Both our carbon and oxygen isotope records exhibit submillennial-scale hydroclimatic oscillations with a characteristic sawtooth-like pattern marked by prominent multi-century drying trends followed by sharp reversals to shorter-term pluvial conditions. A salient feature of our record is that nearly all major drying trends either culminated in or were punctuated by several multidecadal to multicentennial episodes of elevated aridity or megadroughts at 4.9, 4.6, 3.6, 2.8, 1.6, 0.9, 0.4, and 0.2 ka BP. Here, we extend our speleothem records back to the past 13.3 ka BP. Our extended record suggests a long-term drying trend in the context of smoothly increasing austral summer insolation, which is superimposed by gradually increasing amplitudes of multidecadal to multicentennial scale variations since 13.3 ka BP. In this presentation, we will discuss the dynamical nature of hydroclimate change in the SWIO and its teleconnections to the tropical climate variability since the late deglaciation period.
Sub-millennial scale climate variability during the early last glacial period recorded in French speleothems
1School of Earth, Atmosphere and Environment, Monash University, Australia; 2School of Geography, Earth and Atmospheric Sciences, The University of Melbourne, Australia.; 3Laboratoire EDYTEM, UMR CNRS 5204, Université Savoie Mont Blanc, France; 4Australian Nuclear Science and Technology Organisation, Australia.; 5Inrap and TRACES - UMR5608, Jean Jaurès - Toulouse University; 6Institute of Global Environmental Change, Xi’an Jiaotong University, China; 7Aven d’Orgnac, Grand site de France, France
The last glacial period (115,000 – 11,500 years ago) is characterised by millennial-scale climate changes, known as Dansgaard-Oeschger events, that are clearly recorded in ice-cores from Greenland, and many marine and terrestrial records spanning a range of climate zones. Sub-millennial-scale climate variability is also recorded in Greenland ice core records, in the form of short-lived warming events preceding the main interstadial (precursor events), warming events at the end of interstadials (rebound events) and cooling episodes during interstadials (Capron et al. 2010). This sub-millennial variability is particularly pronounced during the early last glacial period. Sub-millennial events are less well studied than the canonical Dansgaard-Oeschger events, as relatively few records have sufficient temporal resolution to resolve them.
This study presents five new speleothem palaeoclimate records from Saint-Marcel and Orgnac Caves in Ardèche, south-east France, collectively spanning 127 to 87 kyr BP. The replicated d18O and d13C time series provide a comprehensive record of millennial and sub-millennial-scale climate variability, which mirrors events observed in the Greenland ice-core record, suggesting a strong climate coupling between south-east France and Greenland. Interstadial periods are interpreted to be associated with an abrupt increase in soil and vegetation activity, reflecting an increase in temperature, and an increase in the dominance of precipitation of the North Atlantic. A stacked chronology was produced, based on 130 individual uranium-thorium ages, that precisely constrains the timing of the onset of interstadial events. The multi-proxy record provided by the d18O and d13C enables changes in different components of the climate system to be interrogated over sub-millennial events. It is found that changes in temperature and precipitation in Ardèche decoupled over a number of the sub-millennial events. This suggests that the expression of these short-lived events is in some ways distinctly different to the more prominent millennial-scale climate events. Variation in Mg/Ca, Sr/Ca and (234U/238U)0 is also observed across the main stadial-interstadial transitions, the interpretation of which is explored.
Capron, E, Landais, A, Chappellaz, J, et al. 2010, ‘Millennial and sub-millennial scale climatic variations recorded in polar ice cores over the last glacial period’, Climate of the Past, vol. 6, no. 3, pp. 345–365.
High-latitude Northern Hemisphere forcing of the Intertropical Convergence Zone in the tropical Atlantic - South American sector for the las glacial period
1Universidade de Sao Paulo, Brazil; 2Department of Atmospheric and Environmental Sciences, University at Albany; 3Institute of Global Environmental Change, Xi’an Jiaotong University; 4Centro de Geociencias, Universidad Nacional Autónoma de México
A major paradigm in climatology holds that shifts in the mean position of the Intertropical Convergence Zone (ITCZ) were the dominant climatic mechanism controlling rainfall in the tropics during the last glacial period. Millennial-scale changes in ITCZ-related rainfall are documented in detail at sites such as the Cariaco Basin off northern South America. However, longer-term changes in ITCZ-related rainfall remain elusive. For instance, reconstructions of past tropical SST gradients in the Atlantic Ocean and climate model simulations suggest a more southerly ITCZ position reaching 5 to 10º S following the maximum ice-sheet extent in the Northern Hemisphere and northernmost position during its reduction. Our new speleothem record, oxygen and carbon isotopes, affected by the ITCZ and currently located in the middle of it, limits the amplitude of the meridional displacement of the ITCZ during millennial events. Likewise, it shows the influence of the northern hemisphere summer insolation (NHSI), which contributes to the amplification/reduction of those events. We present a new paleo-rainfall reconstruction based on high-resolution speleothem d18O record from northeastern Colombia, that spans most of the last glacial cycle (105 kyr to the present). Our results suggest that the forcing of summer insolation in high northern latitudes could affect the strength and positioning of the ITCZ over northern South America more effectively than local insolation. Colder temperatures and ice sheet growth in the NH pushed the ITCZ southward, increasing rainfall over Colombia, indicating an antiphased pattern with Cariaco in response to orbital forcing. Moreover, the EP record shows a striking relationship with Greenland Interstadials (GI), Stadials (GS) and Heinrich Stadial (HS) events. The GS events are marked by more negative d18O values in the EP speleothems that are consistent with the temperature decrease observed in the Greenland ice core record. New results reinforce the idea of the strong influence of meridional ITCZ movements, southernmost position, on SAMS regime during millennial events associated with phase during HS, GS, and GI events. Likewise, it is highlighted that the forcings that affect the long-term changes in the rainfall of the ITCZ are different from those that operate in the summer monsoon of South America (SASM).
Last Glacial Maximum to present day precipitation changes from speleothem growth rates and climate simulations
1Insitute of environmental physics, Heidelberg University, Heidelberg, Germany; 2School of Geosciences, University of Edinburgh, Edinburgh, United Kingdom; 3Institut für Geowissenschaften, Johannes Gutenberg Universität Mainz, Mainz, Germany; 4unaffiliated, previously at University of Reading, Reading, United Kingdom; 5Department of Geoscience, Geo- und Umweltforschungszentrum,Tübingen, Germany
To reliably predict future climate changes, it is crucial to understand the response of the climate system to past changes in radiative forcing. These are investigated using climate models as well as information extracted from paleoclimate archives. Hydrological changes in past, present, and future are, however, far less understood and more uncertain than changes in temperature. Speleothems are terrestrial paleoclimate archives commonly found in karst systems of the low- and mid-latitudes. Their growth rate changes are hypothesized to reflect local changes in precipitation amount, albeit the response may be non-linear and subject to karst specific processes. Full coverage of glacial-interglacial cycles and high precision dating through U/Th measurements makes them a suitable archive to assess and constrain state-dependent precipitation changes. However, growth features inherent in some speleothem entities, such as large and abrupt changes in growth rates and growth hiatuses, are a challenge for current age-depth modelling methods.
Here, we compare modelled precipitation amount from the Paleoclimate Modeling Intercomparison Project (PMIP), in particular for time slices of the Last Glacial Maximum (around 21,000 years before present) and the Mid-Holocene (around 6,000 years before present), to growth rate changes of speleothems from the global speleothem database SISALv2. We perform case studies on a ensemble of synthetic speleothems to systematically assess the resolution of age measurements necessary to reliably detect and model growth rate changes. These synthetic speleothems cover a large range of characteristic speleothem features observed in the SISALv2 database and are analyzed by six different age-depth modeling methods (linear regression, linear interpolation, copRa, StalAge, Bacon, and Bchron). We find reliable growth rate change detection skill for all age-depth models for a sufficient number of datings, except linear regression. However, the presence of just one hiatus, a feature detected in at least 25% of all SISALv2 records, strongly decreases the models' detection skill. Comparing simulated precipitation changes with speleothems selected from SISALv2 according to these criteria helps to constrain past precipitation changes and subsequently confine uncertainty of future changes.
Orbital-scale variability of precipitation isotopes in Eastern Asia in the isotope-enabled Community Earth System Model
1Center for Climate Physics, Institute for Basic Science, Busan, Republic of Korea; 2Pusan National University, Busan, Republic of Korea
The interpretation of East Asian monsoon speleothem oxygen isotope (δ18O) records is the subject of an ongoing debate. Central to this discussion is the potential for speleothem δ18O to record and preserve information on local rainfall variations. For instance, China's speleothem δ18O records and local monsoon proxies (e.g., Loess 10Be) show no significant co-variance. Previous studies have demonstrated distinct responses to orbital forcing in proxy data from western and eastern Asia. Similarly, a few model studies show relatively weak responses on precipitation δ18O to precessional forcing in central and east China. To develop a better understanding of the mechanisms causing orbital-scale variations in δ18O in East Asian speleothems, we ran a set of novel climate simulations performed with the isotope-enabled Community Earth System Model (iCESM1.2), which simulates global variations in water isotopes in the atmosphere, land, ocean, and sea ice. Using a transient 130,000-year iCESM run, forced by time-varying orbital parameters such as eccentricity, obliquity, and precession, aims to reconcile the Asian monsoon speleothem δ18O conundrum. In a second experiment, simulation was performed to identify the effect of precession maximum (Pmax) and minimum (Pmin). The precession simulations initialized with present-day model configuration and performed with an eccentricity value of 0.0493 to emphasize the precession forcing. Examining the precipitation-δ18O spatial patterns and moisture transport under Pmax and Pmin provides new insights into the mechanisms of East Asian monsoon changes and their manifestation in water isotopes in rain.
Greenland’s sensitivity to atmospheric forcing in the context of the past two millennia
1Research Centre for Astronomy and Earth Sciences, Hungary; 2University of California Santa Barbara, Santa Barbara, CA, USA; 3International Arctic Research Centre, University of Alaska, Fairbanks, AK, USA
Greenland ice sheet (GrIS) melt is projected to further accelerate and contribute to sea-level rise over the coming decades, despite possible limitations of climate models in capturing the GrIS’s observed sensitivity to atmospheric circulation changes. Here, we place this observation-model discrepancy in the context of the past 2000 years, by first imposing the observed (1979-2020) Arctic (>60ºN) winds in the fully-coupled Community Earth System Model with fixed anthropogenic forcing to show that recent changes in the mid-to-upper-tropospheric circulation explain half of the observed Greenland surface warming and ice loss acceleration since 1990. This suggests a pathway for large-scale winds to potentially enhance sea-level rise by ~0.2 mm/year per decade. We further reveal fingerprints of this physical mechanism in paleo-reanalyses and several ice core and oceanic coral proxy records spanning the past two millennia, which reinforces our concern about a mismatch between observations and models of atmospheric forcing driven rapid Greenland melt events with major implications for both global sea-level rise projections and the understanding of past changes over the ice sheet.
Termination 1 Millennial-Scale Rainfall Events Over the Sunda Shelf
1Department of Earth Sciences, University of Oxford, UK; 2Department of Earth Sciences, University of Cambridge, UK; 3Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, USA; 4Division of Geological and Planetary Sciences, California Institute of Technology, USA; 5Department of Earth and Atmospheric Sciences, Georgia Institute of Technology, USA; 6Department of Geography and Earth Research Institute, University of California Santa Barbara, USA; 7Department of Geography, The Ohio State University, USA; 8Climate and Global Dynamics Laboratory, National Center for Atmospheric Research, USA; 9Geography and Environmental Sciences, Northumbria University, UK; 10Gunung Mulu National Park, Sarawak, Malaysia
Recent paleoclimate reconstructions have suggested millennial-scale variability in the Indo- Pacific Warm Pool region coincident with events of the last deglaciation. Here, we present a new stalagmite oxygen isotope record from northern Borneo, which today is located near the center of the region's mean annual intertropical convergence zone. The record spans the full deglaciation, and reveals for the first time distinct oxygen isotope variations at this location connected with the Bølling-Allerød onset and the Younger Dryas event. The full deglaciation in the Borneo stalagmite proxy reconstruction appears remarkably similar to a 20–11 ka transient simulation of rainfall over the area produced using the isotope-enabled Community Earth System Model. In this model, periods of weakened Atlantic Ocean meridional overturning circulation are associated with an anomalous Western North Pacific anticyclone, which is produced in boreal autumn and shifts south over Borneo during boreal winter, causing dry conditions.
A Holocene East Asian monsoon isotope record from South Korea
1Center for Climate Physics, Institute for Basic Science, Busan, Republic of Korea; 2Pusan National University, Busan, Republic of Korea; 3Department of Geology, Kangwon National University, Chuncheon, Republic of Korea
The East Asian monsoon region is home to more than a billion people, and their water supply highly depends on the amount of rainfall in the summer monsoon season (June-September). This has resulted in numerous efforts on paleoclimate reconstructions using speleothem calcite d18O, a proxy generally interpreted to represent the rainwater isotope composition. The interpretation of East Asian monsoon speleothem calcite d18O is, however, under scrutiny for more than a decade. It is well known that speleothem carbonate d18O is depending on cave air temperature, parent water d18O as well as varying degrees of kinetic isotope effects. Although, the parent water d18O is one of the best proxies for rainwater d18O, the interpretation of rainfall d18O is not straightforward either, which calls for additional proxies that can shed light on evaporation conditions at the water vapor’s origin, i.e., the moisture source. In addition, east-west transects suggest that different processes govern the speleothem carbonate d18O values in the East Asian monsoon region.
Recent developments in speleothem fluid inclusion isotope analysis allow to measure hydrogen isotopes at sufficiently high precision to use the d-excess as a proxy for evaporation conditions at the moisture source. Here, we present a new high resolution speleothem carbonate d18O, d13C and fluid inclusion d18O, d-excess record from Majiri Gul, South Korea, located at the eastern East Asian monsoon region. The age-model is based on 15 230Th ages, which shows that the speleothem grew from around 9.0 ka up to present with a growth rate varying between 20 to 50 µm/a. We identified two hiatuses between about 6.7 and 5.0 ka and between 4.0 and 1.2 ka, potentially representing drier climate conditions. Combining the stable isotope measurements from calcite and fluid inclusion, we aim to improve the understanding of interpretations of speleothem d18O in terms of rainfall variations over Eastern Asia. Furthermore, using results from isotope enabled climate simulations, we attempt to address the discrepancy between the eastern and western East Asian monsoon speleothem d18O records.
Last Millennium Trends in South American Summer Monsoon Variability Captured in Proxy Records and Isotope-enabled Climate Models
Department of Environmental and Atmospheric Sciences; University at Albany, SUNY, United States of America
The South American Summer Monsoon (SASM) is the main driver of regional hydroclimate variability across tropical and subtropical South America. Prior to the instrumental era, the best information is provided by a wealth of stable oxygen isotope proxies, many of which are calcite records found in South American caves, that archive more regionally integrated hydroclimate information than proxies for local precipitation alone. Network studies that include proxy records from a wide spatial domain can isolate shared variability, separating regional controls from local influences. Comparing paleorecord signals with isotope-enabled climate models lends particular insight into various large-scale environmental characteristics that modulate hydroclimate such as atmospheric circulation, changes in the regional energy budget, and can link the climate system response to external forcings. A Monte Carlo Empirical Orthogonal Function (MCEOF) decomposition of 14 δ18O paleorecords (12 speleothems, 1 ice core, and 1 lake sediment core) and 2 isotope-enabled climate models over the Last Millennium (LM; 850 – 1850 CE) finds leading modes corresponding to the Bolivian High – Nordeste Low system and variability in southeastern Brazil corresponding to the region of South Atlantic Convergence Zone variability with multi-centennial mean-state shifts during the MCA and LIA.
An extension of this analysis into the current warm period (CWP; 1850 -- 2000 CE) was conducted with 8 δ18O records (6 speleothems, 1 ice core, and 1 lake sediment core). We use both paleorecords and an atmosphere-only isotope-enabled climate model (iCAM5) to explore the role of natural variability and external forcings in controlling the variability of the South American Summer Monsoon and compare the atmospheric circulation response in the CWP with the climatology of the LM. Our results show an enrichment trend in the first EOF mode, indicating a return of the proxy network isotopic values to levels seen prior to the multi-centennial depletion of heavy isotopes that occurred during the LIA. While the trend toward more positive δ18O values is seen in both paleorecords and isotope-enabled climate models, these values have not yet exceeded the range of variability constrained by LM climate. We find that while SASM variations over the LM have resulted primarily from internal variability, the anthropogenic greenhouse gas forcing over the last 70 years has played an increasingly dominant role in driving isotopic enrichment of isotopic paleorecords across the monsoon basin.
Can past climates constrain clouds and convective parameterizations in climate models?
1William Paterson University, United States of America; 2NASA Goddard Institute for Space Studies, New York, NY, USA; 3Department of Geosciences, The University of Arizona, Tucson, AZ, USA; 4Department of Earth and Atmosphere Sciences, University of Quebec in Montreal, Montreal, Canada; 5Climate and Global Dynamics Laboratory, NCAR; 1850 Table Mesa Drive, Boulder, CO USA
Estimations of equilibrium climate sensitivity (ECS) is sensitive to the cloud and convective parameterizations of complex general circulation models. These parameterizations also directly influence water isotopes, providing a tool to flag unrealistic parts of the parameterization phase space. We provide a proof-of-concept study to constrain these parameterizations in a perturbed parameter ensemble of atmosphere-only simulations by evaluating model biases in the present-day runs using multiple satellite climatologies and, by comparing simulated d18O of precipitation (d18Op) with a global database of speleothem d18O records covering the Last Glacial Maximum (LGM), mid-Holocene (MH) and pre-industrial (PI) periods. Relative to modern, paleoclimate simulations show greater sensitivity to parameter changes, allowing for evaluating model uncertainties over a broader range of climate forcing and identifying parts of the world that are parameter sensitive. Certain simulations (all weighted by sensitivity scores) reproduced LGM and MH d18Op anomalies from the PI better than the default parameterization. Not a single set of parameterizations worked well in all climate states, thus improving simulations requires determining all plausible parameter combinations, potentially narrowing ECS range.
Modeling of Stable Water Isotopes under Modern Day and LGM climate conditions using the EMAC climate simulation system
Johannes Gutenberg Universität, Germany
Speleothem d18O values depend on a complex interplay of various processes occurring in the atmosphere, the soil and karst above the cave as well as during precipitation of speleothem calcite. Thus, the relationship between speleothem d18O values and climate parameters, such as local and supra-regional temperature and precipitation patterns, is in many cases not straightforward.
Here we present a set of global simulations for the Modern Day (MD) and Last Glacial Maximum (LGM) period with a duration of 20 years, both performed with the EMAC atmospheric chemistry general circulation model, being enhanced with stable water isotope diagnostics. The model resolution comprises of a horizontal grid of 0.88° × 0.88° (T106) and a vertical resolution of 31 model levels (top level at 0.01 hPa). The simulated d18O values in precipitation were converted into synthetic speleothem d18O records by accounting for the effects of evapotranspiration and infiltration using the model of Haude (1954) as well as the drip-water-to-calcite fractionation equation by Tremaine et al. (2011). We then calculated mean speleothem d18O values on an annual and seasonal basis, weighted by the amount of precipitation and infiltration (pw-d18O, iw-d18O), respectively. The synthetic speleothem d18O records were compared with speleothem d18O records from the Speleothem Isotopes Synthesis and Analysis Working group (SISAL) database [Comas Bru et al., 2020].
In general, the model setup is capable of adequately simulating the global pattern of d18O values in precipitation for both the MD and the LGM scenario. The synthetic speleothem d18O records clearly benefit from weighting by the amount of precipitation and, partly, even more from weighting by infiltration (i.e., the application of an evapotranspiration model). This is obvious by the better agreement of iw-d18O speleothem records with the SISAL data for regions with an infiltration-to-precipitation ratio <0.7. The corresponding regions often exhibit a seasonal climate, with pronounced arid and humid seasons (e.g., the Mediterranean Region). In temperate regions, such as Central Europe, the iw-d18O is approximately similar to the corresponding pw-d18O. Thus, infiltration in these regions seem to be less influenced by evapotranspiration and surface runoff. The evapotranspiration model of Haude (1954) is developed for temperate regions, but has limitations when calculating evapotranspiration in extremely arid and/or cold areas, possibly resulting in biased iw-d18O values. Commonly, the climate of these regions is too harsh for speleothem growth, and therefore currently not subject of this study. In further studies, this problem could be addressed by using different evapotranspiration models, which are specifically developed for arid and/or cold climate conditions.
Comas-Bru, L. et al., 2020: SISALv2: A comprehensive speleothem isotope database with multiple age-depth models. Earth System Science Data 12, 2579–2606.
Haude, W., 1954: Zur praktischen Bestimmung der aktuellen und potentiellen Evaporation und Evapotranspiration, Schweinfurter Dr. und Verlag-Ges..
Tremaine, D. M. et al., 2011: Speleothem calcite farmed in situ: Modern calibration of δ 18O and δ 13C paleoclimate proxies in a continuously-monitored natural cave system, Geochim. Cosmochim. Ac., 75, 4929–4950, https://doi.org/10.1016/j.gca.2011.06.005.
Fluid inclusion microthermometry in stalagmites: The next stage of development
1Department of Earth Science, University of Bergen, Norway; 2Bjerknes Centre for Climate Research, University of Bergen, Norway; 3Department of Earth Sciences, University of Oxford, UK
Fluid inclusion microthermometry is one of the analytical approaches that has been proposed for speleothem-based temperature reconstructions (Krüger et al. 2011). The proxy of this paleothermometer is the density of former drip water that became enclosed in microscopic fluid inclusions during speleothem growth. The microthermometry method relies on measurements of the liquid-vapour homogenisation temperature of the fluid inclusions, which is determined by the water density and the inclusion volume. By applying a thermodynamic model that takes account of the volume-dependent effect of surface tension on the measured homogenisation temperature (Marti et al. 2012) the water density, and thus, the formation temperature of a fluid inclusion, i.e., the cave air temperature, can be calculated. The analytical precision (2SD) of the method ranges between 0.1 and 0.3 ºC depending on the size of the inclusions.
Cave temperature reconstructions based on fluid inclusion microthermometry rely on four fundamental assumptions:
1. The density of the drip water trapped in the fluid inclusions is controlled solely by cave temperature.
2. Fluid inclusions are closed systems that preserve the original physical and chemical properties of the enclosed drip water over geological times scales.
3. The closing age of the inclusions is equal to the age of the surrounding calcite.
4. The pure water system is an adequate approximation to describe the physico-chemical properties of natural cave drip waters.
If these assumptions were perfectly met, we would expect that fluid inclusions from the same stalagmite growth layers yield identical formation temperatures within analytical precision. And consequently, one single fluid inclusion would be sufficient to determine the cave temperature at a specific point in time. In reality, however, we observe a systematic scatter of temperatures of 3 – 6 ºC derived from inclusions of the same growth layers. This is one order of magnitude larger than the analytical precision and distinctly exceeds the amplitude of short-term natural cave temperature variations. The observed scatter of the temperature data, therefore, suggests that at least one of the aforementioned assumptions is incorrect or describes the system inadequately.
The objective of the next stage of development of the microthermometric approach, therefore, is to scrutinize the method’s fundamental assumptions in search of potential non-thermal factors that have not yet been considered and that may explain the observed scatter of the temperature data. Our research is still in the early stages, and hence, the presentation at KR9 focuses mainly on the experimental and analytical approaches we pursue to achieve this goal.
Krüger, Y., et al., 2011. Chem.Geol. 289, 39-47.
Marti, D., et al., 2012. Fluid Phase Equilibria 314, 13-21
Residual speleothem powder samples can be used to characterize magnetic mineral assemblages for paleo-environmental studies
1Institute for Rock Magnetism, Dept. of Earth & Environmental Sciences, University of Minnesota, USA; 2Dept. of Earth and Planetary Sciences, University of California, Davis, USA; 3Institute of Earth Science, Hebrew University of Jerusalem, Israel; 4Institute of Human Origins, Arizona State University, USA
<p>Speleothems are valuable archives of past climate conditions and are commonly sampled as powders using a micro-mill or similar small scale drilling equipment for U-Th dating or other geochemical analyses. Here we demonstrate that these very same powders can also be used to collect complementary data on the magnetic mineral assemblages within speleothems. Iron oxides and oxyhydroxides commonly occur in trace concentrations within speleothems and their quantity, mineral compositions, and grain size distributions have been shown to vary systematically in response to local environmental conditions at the surface immediately overlying cave systems. Thus, variations in magnetic mineral assemblages can capture changes in average precipitation, flooding events, overlying soil conditions, as well as hydrologic changes within karst systems. In this study, we tested the use of small amounts (100s of µg) of micro-milled powder from South African stalagmites originally collected for U-Th dating as a means for characterizing the magnetic mineral assemblages in the stalagmites. Low temperature magnetometry and vibrating sample magnetometry (both standard techniques in the materials science community) show the presence of maghemite, goethite, and hematite, all of which have been reported in previous speleothem studies. The maghemite is consistent with that produced in soils, suggesting that pedogenic contributions to the stalagmite are likely. The goethite is likely produced <em>in-situ</em> in the stalagmite, while the hematite displays magnetic behavior (Morin Transition) consistent with larger detrital grains. Profiles of how the concentrations of these different magnetic components change in time can be used as an independent source of paleo-environmental information. Magnetic measurements do not require any alteration of the powder as no acids or solvents are used. This approach offers paleoclimate researchers the potential to glean additional data from the powders they have already collected for geochemical and isotopic analyses.</p>
Investigating δ13C values in stalagmites from tropical South America
1Department of Geology, Trinity College Dublin, Ireland; 2Department of Geosciences, University of Tübingen, Germany; 3Departamento de Geoquímica, Universidade Federal Fluminense, Brazil; 4Instituto de Geociências, Universidade de São Paulo, Brazil; 5Earth Observatory of Singapore, Nanyang Technological University, Singapore; 6Department of Atmospheric and Environmental Sciences, University at Albany; 7Instituto Geofísico del Perú, Peru; 8Institut des Sciences de la Terre d’Orléans, France; 9Faculty of Geosciences and MARUM-Center for Marine Environmental Sciences, Germany; 10Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Brazil; 11Center for Nuclear Energy in Agriculture (CENA), Universidade de São Paulo, Brazil; 12Jackson School of Geosciences, University of Texas, USA; 13HFML-FELIX, Faculty of Science, Radboud University, The Netherlands; 14Max Planck Institute for Chemistry, Germany; 15Geology Department, Trier University, Germany; 16College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, USA; 17Department of Earth Sciences, University of Southern California, USA; 18Earth and Planetary Sciences, University of California Berkeley, USA; 19Institute of Global Environmental Change, Xi'an Jiaotong University, China; 20Department of Geosciences, University of Massachusetts, Amherst; 21Department of Earth Sciences, University of Minnesota, Minneapolis
Multiple factors control δ13C values in speleothems and complicate their paleoclimatic and paleoenvironmental interpretation. Therefore, most studies avoid the presentation of δ13C values, focusing solely on δ18O. This development can be observed with regard to most recent cave studies from tropical South America, in which stalagmite δ18O were preferentially published without the consideration of δ13C data. Here we present a large δ13C dataset of 98 speleothem records covering multiple time scales from South America, of which 42 remained unpublished or were not available until now. Our main objective is concentrating on the support of existing and emerging databases, such as SISAL, and providing new data for the speleothem and climate modeling communities.
As a first approach, we review the δ13C values for the last two millennia and evaluate the environmental factors influencing this proxy, e.g., local hydroclimate, altitude, temperature, and abundant vegetation types. Our results indicate that the main factors controlling variations in δ13C values are: changes in the local hydroclimate and, to a minor extent, temperature. For this time period, most of the isotope records show a significant correlation between the δ13C and δ18O values, indicating a close relationship between local hydroclimate and large-scale atmospheric processes related to shifts of the South American Monsoon System (SAMS). Furthermore, in most of the karst systems studied here, the predominant occurrence of C3 plants growing on soils above the caves are responsible for a considerable drop in δ13C values (≤6‰) for most of the speleothems.
Deuterium excess and 17O-excess in South Korean rainfall
1IBS Center for Climate Physics, Busan, Republic of Korea; 2Pusan National University, Busan, Republic of Korea
Rainwater δ18O is affected by both temperature-dependent equilibrium and kinetic fractionation processes. Combined with fractionation occurring in the epikarst and cave environment, the interpretation of speleothem carbonate δ18O is therefore challenging, especially without monitoring rain and cave drip water δ18O. Speleothem fluid inclusion δ18O is independent of fractionation during carbonate precipitation and is thus less difficult to interpret but is still rather complex. Speleothem and rainwater d-excess derived from the combined measurement of hydrogen and oxygen isotope analysis, on the other hand, is only affected by kinetic fractionation processes during evaporation. Speleothem fluid inclusion isotope analysis may thus contribute significantly to our understanding of both speleothem carbonate δ18O as well as the hydrological cycle.
To interpret d-excess in speleothem fluid inclusions, a thorough assessment of rainwater d-excess is required. The kinetic fractionation at the moisture source associated with evaporation conditions is determined by the relative humidity contrast between the ocean surface boundary layer and the overlying air column, wind speed, and sea surface temperature. Sub-cloud evaporation and moisture recycling may also affect d-excess. 17O-excess is affected by similar processes as d-excess but is less sensitive to sub-cloud evaporation and temperature.
We present a 2-year dataset of monthly rainwater d-excess and 17O-excess from Busan, South Korea. The d-excess shows a strong seasonal cycle with an amplitude of approximately 15-20‰. High values occur during the dry winter monsoon season and low values during the humid summer monsoon season. Interestingly, the 17O-excess trend deviates from d-excess in November and December 2020. By combining these two proxies for evaporation conditions and local weather data, we aim to enhance our understanding of evaporation conditions at the moisture source to increase our confidence in the interpretation of carbonate and fluid inclusion δ18O, and in particular fluid inclusion d-excess.
Ba isotope composition of Holocene secondary carbonates
Johannes Gutenberg University Mainz, Germany
In recent years, the interest in variations of barium (Ba) isotope composition in environmental and geological research has increased. So far, many studies have focused on the method development, such as analytical techniques, column chromatography separation methods and analysis of various reference materials (e.g., An et al., 2019; Miyazaki et al., 2018; Nan et al., 2015). We apply these methods to annually laminated calcareous sinter samples from Roman aqueducts.
We analyse the samples in a standard-sample bracketing approach using a Neptune Plus MC-ICP-MS without prior addition of a spike. To avoid that the resulting δ134/137Ba isotope ratios are influenced by mass fractionation effects inside the mass spectrometer, the intensity of the measured Ba signal is matched to the intensity of the bracketing standard prior to measuring the sample. Although a variability in intensity of ±30 % does not lead to significant differences for Ba isotopes, we try to stay within a variation of ±10 % between sample and standard.
Our first tests regarding the Ba isotope composition of carbonates showed promising results. Depending on the sample material, Ba isotope variations may even be visible on an annual scale. Roman aqueduct sinter provide ideal samples for this due to their often thick layers, which allow for multiple samples taken from one layer. A combination of Ba isotopes with established proxies, such as trace elements and carbon and oxygen isotope ratios, and precise 230Th/U-dating may provide new insights into past climate conditions.
An, Y. J., Li, X., and Zhang, Z. F. (2020). Barium Isotopic Compositions in Thirty‐Four Geological Reference Materials Analysed by MC‐ICP‐MS. Geostandards and Geoanalytical Research, 44(1), 183-199.
Miyazaki, T., Kimura, J. I., Wakaki, S., Vaglarov, B. S., and Haraguchi, S. (2018). Determination of stable isotope ratios of Ba by 130Ba–135Ba double-spike total evaporation method using thermal ionization mass spectrometry (DS-TEV-TIMS). JAMSTEC Report of Research and Development, 27, 109-118.
Nan, X., Wu, F., Zhang, Z., Hou, Z., Huang, F., and Yu, H. (2015). High-precision barium isotope measurements by MC-ICP-MS. Journal of Analytical Atomic Spectrometry, 30(11), 2307-2315.
A comparative study of Ca isotope ratios with rainfall, δ13C, and trace element data from three US cave systems
1Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, TN, USA; 2School of Earth Sciences, The Ohio State University, Columbus, OH, USA; 3Department of Earth and Environmental Sciences, University of Kentucky, Lexington, KY, USA; 4Department of Earth Sciences, University of Cambridge, Cambridge, UK
The development of quantitative records of past rainfall is an outstanding goal in the field of speleothem paleoclimatology and represents an essential step for benchmarking paleoclimate model simulations. However, most traditionally employed speleothem proxies, including δ18O, δ13C, and trace element to calcium ratios, respond to a number of complex climatic and environmental influences and typically provide only qualitative estimates of paleoclimate change. Variations in speleothem Ca ratios (δ44Ca) are uniquely controlled by calcite precipitation in the epikarst or on the cave ceiling (prior calcite precipitation, or PCP), which can be modeled as a Rayleigh fractionation process and calibrated using modern rainfall data. Thus, speleothem δ44Ca shows promise as a (semi) quantitative proxy for past changes in local effective rainfall rates. However, few rigorous cave monitoring studies have focused specifically on Ca isotope cycling in cave systems and the ways in which important factors, like host rock δ44Ca variability and geology, epikarst thickness, ventilation, and seasonal rainfall distribution affect δ44Ca signals in speleothems are not well understood.
Here we present a comparative study of δ44Ca data and coeval measurements of δ13C and trace element ratios, established proxies for water infiltration, from cave drip waters, farmed calcite, and host rocks from three different cave systems - White Moon Cave (WMC) in coastal California, Lake Shasta Caverns (LSC) in northern California, and Blue Springs Cave (BSC) in east-central Tennessee. Our three cave systems are characterized by different hydroclimate, geology, flow path geometry, and seasonal infiltration characteristics. WMC and LSC experience a similar modern Mediterranean climate with >80% of precipitation occurring during the winter while BSC experiences a humid subtropical climate with little seasonal variation in rainfall. WMC is hosted within marble bedrock while LSC and BSC formed in less metamorphosed limestone. To assess the relationship between Ca isotope cycling and effective rainfall we also compare cave system δ44Ca data with rainfall rates from nearby weather stations and supplement these comparisons with drip rate information when possible.
The comparison of WMC, LSC, and BSC δ44Ca, δ13C, and trace element data from drip sites with different flow path geometry and from caves in different geologic and climate settings allows for these key factors to be assessed independently. This work, and the direct comparison between δ44Ca measurements and measured local rainfall rates in particular, aids in the refinement of speleothem δ44Ca as a new, (semi) quantitative proxy for paleorainfall.
ICER carbonate clumped isotope analysis of karst deposits
1Institute for Nuclear Research, Debrecen, Hungary; 2Isotoptech Ltd., Debrecen, Hungary
In April 2018, a 253 Plus 10 kV isotope ratio mass spectrometer equipped with a Kiel IV automatic carbonate device (Thermo Scientific) was installed at the Isotope Climatology and Environmental Research Centre (ICER), Institute for Nuclear Research, Debrecen, Hungary. Beside the analysis of the conventional carbon and oxygen isotope composition of small carbonate samples, the main application of our system is the clumped isotope thermometry of different kind of carbonate samples. The clumped carbonate measurements are carried out following the methodology of Bernasconi et al. . Carbonate replicate samples (100-110 μg) are digested by three drops of 1.95 g/cm3 phosphoric acid in the Kiel IV carbonate device. The evolved CO2 is passed through a micro-volume inlet system, which contains two LN2 traps and a Porapak trap in order to eliminate the possible hydrocarbon contaminants. The Easotope software is used for data evaluation of the measurements using the Brand parameters  and the carbon dioxide equilibrium scales [3, 4]. To demonstrate the achievable accuracy, precision and long-term stability of the measurement system at ICER, we analyzed international carbonate reference materials and proposed standards (ETH4, IAEA-C1, IAEA-C2, NBS-18, NBS-19, Merck Carbonate) and naturally formed travertine samples (known formation temperatures are in the range of 5-95°C) and compared them to formerly published data of two reputable laboratories from the clumped community [1, 5].
We also applied clumped carbonate analysis to several karst related research topics. One aspect is the suitability of tufa deposits as a paleoclimate archive, even if kinetic fractionation might play a significant role during carbonate formation. Another aspect is the application of clumped isotope thermometry to mammillary speleothems and hydrothermal carbonates as part of paleoclimate and speleogenetic studies.
In the poster we will present our current achievements in the field of carbonate clumped isotope measurement, as well as some results on clumped isotope analysis of various carbonate deposits (tufa, mammillary speleothems, hydrothermal carbonates, dolomites) from different karst environments.
 Bernasconi et al. (2018). Geochemistry, Geophysics, Geosystems, 19(9), 2895-2914. https://doi.org/10.1029/2017GC007385
 Brand et al. (2010). Pure and Applied Chemistry, 82(8), 1719-1733. https://doi.org/10.1351/PAC-REP-09-01-05
 Dennis et al. (2011). Geochimica et Cosmochimica Acta, 75(22), 7117-7131. https://doi.org/10.1016/j.gca.2011.09.025
 Bernasconi et al. (2021). Geochemistry, Geophysics, Geosystems, 22(5), e2020GC009588. doi:10.1029/2020GC009588
Anderson et al. (2021). Geophys Res Lett., 48(7):e2020GL092069. doi:10.1002/ESSOAR.10505702.1
Using Magnetically Enhanced Laminae in Speleothems as a Paleoprecipitation and Paleoflood Proxy
1Harvard University, United States of America; 2Universidade de Sao Paulo, Brazil; 3Universidade Federal Fluminense, Brazil
Common existing paleoprecipitation proxies such as d18O can be measured at high spatial and temporal resolution but respond to multiple aspects of the climate system, resulting in ambiguity in their interpretation. The concentration of ferrimagnetic iron oxide particles in loess-paleosol sequences and speleothem laminae has been recognized as a potential paleoprecipitation proxy that can be used in conjunction with existing indicators to more accurately isolate a rainfall signal, particularly with regard to extreme weather events. However, the mechanism of magnetic enhancement in speleothems, which may include aeolian, floodwater, and dripwater delivery, appears to vary by location, introducing uncertainty to the magnetism-rainfall relationship.
To isolate the effect of flooding on speleothem magnetic enhancement, we examine speleothem MFZ-N1 from Malfazido cave in Paraná, southern Brazil. MFZ-N1 was collected from about 100 meters inside the cave in a section subject to repeated flood events. U-Th ages obtained from the sample span 1100-2007 CE over a length of 200 mm, implying an average growth rate of 0.22 mm y-1. We impart a saturation isothermal remanent magnetization (IRM) to the speleothem, then use the recently developed high-sensitivity Quantum Diamond Microscope (QDM) to produce micrometer resolution magnetic maps of ferrimagnetic particle concentration in the MFZ-N1 central column. Following QDM imaging, we integrate the magnetic field intensity along each lamina to construct a time series that can be compared to local rainfall records from the past century.
Compared to speleothems from less flood-prone cave locations documented in other speleothem magnetism studies, the ferrimagnetic particles found in MFZ-N1 have individually stronger magnetic moments. In addition, these particles are sparsely spatially distributed, with the exception of isolated, 100 µm thick laminae at 1-10 mm intervals that contain high concentrations of these particles. We hypothesize that these highly enriched laminae are the results of cave flooding events corresponding to extreme rainfall events while the sparsely distributed background particles were introduced via a distinct mechanism.
In our ongoing work we will use comparison to documented heavy rainfall events in the local region to test this hypothesis. In addition, we will conduct an alternating field demagnetization sequence on the sample to extract the coercivity spectrum of each distinct ferrimagnetic grain population. This spectrum will then be compared to those from grain populations identified in previous environmental magnetism studies to fingerprint the source of the grains. These comparisons, applied to a statistically representative set of enrichment horizons, may be able to identify rock magnetic properties unique to flood deposit layers, making high-resolution magnetic study a means of identifying such events in speleothems beyond the historic period.
Method development for precise determination of d238U in limestone
1Institute for Nuclear Research, Debrecen, Hungary; 2Department of Geology, Eötvös University, Budapest, Hungary; 3MTA-MTM-ELTE Research Group for Paleontology, Eötvös University, Budapest, Hungary
From the three naturally occurring uranium isotopes, the 238U/235U isotope ratio is considered as a constant value for certain calculations, such as 234U/230Th dating of speleothems. However, in some cases, the d238U values calculated from this ratio also show changes of up to 1 permil (d238U is defined as (RSample/RCRM112A–1)·1000, where RSample and RCRM112A refer to the 238U/235U ratio of the sample and the CRM112A international uranium standard material). This difference is connected to a change in the dissolved oxygen content of the ancient ocean triggered by extreme climatic shifts at major events in Earth’s history, such as at the end of the Triassic. d238U in marine carbonates is a novel proxy for the reconstruction of global seafloor redox conditions. Here we present new developments in the method for chemical preparation, and the measurement protocol using a Thermo Scientific Neptune Plus multicollector ICP-MS instrument installed in January 2019. Twenty-eight limestone samples from the Triassic-Jurassic boundary section at Csővár (Hungary) were prepared for d238U determination. Each limestone sample was powdered and 1 gram of them was dissolved overnight in twice distilled HCl using trace-metal free centrifuge tubes. After that, the samples were filtered through a cellulose acetate syringe membrane filter with a 0.45 micron pore size. A double uranium spike solution was added to the samples, in order to correct the instrumental mass bias. The spike/sample ratio was set as 233U/235U ~2–3. The samples were then fully evaporated and digested at least 2 times with twice distilled, concentrated nitric acid. Then they were redissolved in 3 mol/dm^3 nitric acid, as it is suitable for the following column chemistry, using UTEVA ion exchange resin (100–150 um particle size). Thorium was removed from the column with 5 mol/dm^3 HCl/0.05 mol/dm^3 citric acid, the uranium fraction was eluted with 15 ml 0.05 mol/dm^3 HCl solution. During measurement, the sensitivity of the mass spectrometer was tuned at around 2% (2000 V/ppm). Each intensities were measured with Faraday collectors, the 233U, 235U, and 236U ion beams were measured with 10^13 Ohm amplifiers, because of the better signal-to-noise ratio of this technology. The 238U ion beam was measured with 10^11 Ohm amplifier. Each sample was measured at least three times with standard–sample bracketing. The standard solution for the measurements was a mixture of CRM112A uranium reference material and the IRMM 3636a double uranium spike solution. During the evaluation, the contribution of 235U and the 238U from the spike was also taken into consideration. The analytical errors of our measurements were between 0.02‰ and 0.12‰ (±1s). Our measured data and the analytical uncertainty fit quite well to the previously published results in the literature. A major negative d238U anomaly was detected in the limestone deposited during and after the end-Triassic mass extinction. It indicates severe and extensive marine anoxia, which probably played a key role in delaying the biotic recovery after the extinction. The generated uranium isotope curve is only the second set of d238U data worldwide across the Triassic-Jurassic boundary interval.
New developments in speleothem organic carbon isotope analysis as a proxy for terrestrial ecosystem dynamics
1Department of Chemistry, Biochemistry and Pharmaceutical Sciences & Oeschger Centre for Climate Change Research, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland; 2Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
Terrestrial ecosystems are an important component of the global carbon cycle, but their response to ongoing anthropogenic climate change remains poorly constrained. Speleothems can serve as a precisely dated, high resolution archive of ecosystem processes occurring at cave catchment scale.
We present preliminary results from an ongoing method development study that aims to extract and measure the isotopic composition of organic carbon entrapped in speleothems. Speleothem organic carbon is likely sourced from the vegetation, soil and karst overlying the cave, and its carbon isotopic ratios (δ13C and 14C) may act as a direct tracer for ecosystem dynamics. Our results are based on a previous protocol by Lechleitner et al. (2019), which describes a rapid, low contamination method for carbon isotope analysis of the speleothem non-purgeable organic carbon (NPOC) fraction for small samples (<150 mg CaCO3). Decarbonation of acid digested carbonate samples is followed by wet chemical oxidation of the NPOC and analysis of the resulting headspace CO2 via mass spectrometry to determine its isotopic composition. Our results include a detailed blank assessment which allows us to pinpoint possible contamination sources, and a new protocol that includes monitoring of the CO2 flow during decarbonation and NPOC analysis, ensuring complete removal of inorganic carbon prior to the oxidation step and allowing for very precise quantification of the amount of organic carbon present in the sample.
These results reiterate the great promise of this method to provide accurate, ecosystem-level information on past terrestrial environments at comparatively high temporal resolution.
Lechleitner, F.A., Lang, S.Q., Haghipour, N., McIntyre, C., Baldini, J.U.L., Prufer, K.M., Eglinton, T.I., 2019. Towards organic carbon isotope records from stalagmites: coupled d13C and 14C analysis using wet chemical oxidation. Radiocarbon 61, 749–764. doi:10.1017/RDC.2019.35
COUPLING STALAGMITE GROWTH MODELS AND CAVE MONITORING: A CASE STUDY IN CUEVA DE DON JUAN (VALENCIA, SPAIN)
1Dpto. de Geodinámica, Estratigrafía y Paleontología. Facultad de CC. Geológicas, Universidad Complutense de Madrid, Madrid, 28040, Spain; 2Instituto de Geodiencias (UCM-CSIC), Madrid, 28040, Spain; 3Unidad de Geología Ambiental, Dpto. de Medioambiente, CIEMAT, Madrid, 28040,Spain; 4Generalitat Valenciana, CADRECTE, Valencia, 46018, Spain
Environmental monitoring outside and inside caves provides information on main parameters controlling cave processes, stalagmites growth dynamics and transference of climatic information. Furthermore, stalagmite growth models (SGMs) can be used as a way to calculate stalagmite growth rates, and to assess which parameters dominate calcite deposition (e.g. Ca2+, drip rate, temperature, CO2, etc.). The calibration of SGMs with environmental monitoring in caves provides a powerful tool to recognize parameters and processes influencing stalagmites growth. Thus, the calibrated models can be used to infer past environmental changes and future evolution of the cave. For this work we have focussed on understanding the present-day growth rates of stalagmites in a touristic cave, Cueva de Don Juan (Jalance, Valencia), with a markedly Mediterranean climate, as a basis for later models on past and future climatic fluctuations and scenarios (warming, increase in tourism…).
We chose various places to monitor inside the cave with specific protocols that includes recording of a variety of parameters from which temperature, carbon dioxide, drip rate, water chemistry and current growth rates are herein considered. We compare theoretical stalagmite growth rates calculated through two different models (Vieten and Hernández, 2021; and Baker et al, 2014). Both models are based on the equations proposed by Dreybrodt (1988) but present slight differences in the calculation of the kinetic reaction constant (α). Vieten and Hernández (2021) define α as dependent on temperature only, while Baker et al., (2014) include the dripwater film thickness (δ) as well. For this reason, we used three different film thickness (δ=0.04mm, δ=0.1mm and δ=0.3mm), as well as monitoring data of two selected sites to calculate the theoretical stalagmite growth rates according to both models and to compare them with the observed growth rates in Cueva de Don Juan. On the basis of the results, we discuss the reliability of both models and the main factors contributing to the low growth rates obtained during the monitoring period.
Contribution to Project CGL2017-83287-R (MICINN, Spain) and to research group ‘‘Sedimentary Geology, Paleoclimate and Environmental Change’’ (UCM, Spain).
Baker, A.J., Mattey, D.P and Baldini, J. U.L., 2014. Reconstructing modern stalagmite growth from cave monitoring, local meteorology, and experimental measurements of drip water. Earth and Planetary Science Letters 392, 239-249.
Dreybrodt, W., 1988. Processes in Karst Systems: Physics, Chemestry and Geology. Springer Series in Physical Environment, vol.4. Springer-Verlag, Berlin, 288pp.
Vieten,R. and Hernández, F., 2021. StalGrowth-A Program to Estimate Speleothem Growth Rates and Seasonal Growth Variations. Geosciences 2021, 11, 187.
Disequilibrium carbon and oxygen isotope fractionation in speleothems - results from a new advection-diffusion-reaction model
1Institute for Geosciences, University of Mainz, Germany; 2Department of Earth and Planetary Sciences, Weizmann Institute of Science, Israel
It has been known since the late 1960’s that speleothem calcite - in most cases - does not precipitate in stable isotope equilibrium with the drip water and the dissolved inorganic carbon (DIC). Thus, the conventionally used equilibrium carbon and oxygen isotope fractionation factors cannot be used to describe stable isotope fractionation. To explain this phenomenon, many studies invoked terms like “rapid degassing” of CO2 from the thin films of solution on the surface of a speleothem, but the speleothem literature shows many misunderstandings of the related effects on stable isotope fractionation.
Previous approaches to describe the temporal evolution of the δ13C and δ18O values of the DIC (e.g., Deininger and Scholz, 2019) were able to reasonably explain some of the observed effects. However, the description of some aspects, such as calcite precipitation as well as isotope exchange with the CO2 of the cave atmosphere, the drip water and the calcite surface below the solution film, remained incomplete.
Here we present a new advection-diffusion-reaction model (Sade et al., 2022), considering the temporal evolution of all species of DIC (CO2, HCO3-, CO32-), precipitation and dissolution of speleothem calcite at the water-mineral interface, degassing of CO2 as well as carbon isotope exchange with cave CO2 for a thin film of solution flowing down inclined surfaces. Comparison with laboratory experiments with synthetic carbonates (Hansen et al., 2019) enables us to validate our model and constrain kinetic isotope fractionation factors.
We test the sensitivity of the isotopic composition of the precipitated calcite along inclined surfaces on discharge rate and the surface slope. Calcite δ13C and δ18O values correlate well with the degree of prior calcite precipitation (PCP), which is a major determinant of speleothem δ13C and δ18O values. At low PCP, speleothem δ13C and δ18O values may initially decrease relative to calcite-DIC and calcite-water equilibrium due to expression of kinetic isotope effects of mineral precipitation. With progressive PCP, δ13C and δ18O values will gradually increase due to continuous formation of CO2(aq) and degassing. This shift in the isotopic composition of the calcite to initially lower-than-equilibrium, but then higher-than-equilibrium values may expand the regime of near equilibrium δ13C and δ18O values. This may allow quantitative environmental reconstructions, even when the isotopic system is not in equilibrium.
Deininger, M. and Scholz, D. (2019) ISOLUTION 1.0: an ISOtope evoLUTION model describing the stable oxygen (d18O) and carbon (d13C) isotope values of speleothems. International Journal of Speleology 48, 21-32.
Hansen, M., Scholz, D., Schöne, B.R. and Spötl, C. (2019) Simulating speleothem growth in the laboratory: Determination of the stable isotope fractionation (d13C and d18O) between H2O, DIC and CaCO3. Chemical Geology 509, 20-44.
Sade, Z., Hegyi, S., Hansen, M., Scholz, D. and Halevy, I. (2022) The effects of drip rate and geometry on the isotopic composition of speleothems: Evaluation with an advection-diffusion-reaction model. Geochimica et Cosmochimica Acta 317, 409-432.
Quantifying kinetic effects on the fractionation of traditional and non-traditional stable isotopes during (speleothem) CaCO3 formation: Novel high precision laboratory experiments
1Institute for Geosciences, University of Mainz; 2Climate Geochemistry Department, Max-Planck-Institute for Chemistry, Mainz
Speleothems are well known as valuable terrestrial paleoclimate archives because they provide important insights into past environmental and climate variability. Unfortunately, speleothem calcite usually precipitates out of stable isotope equilibrium. The mechanisms behind these (disequilibrium) fractionation processes have been discussed in several modeling[1,2] and laboratory approaches. However, a final validation, which approach is best suited for (quantitative) interpretation of speleothem isotope records remains impossible so far.
Here we present first results of novel laboratory experiments, investigating the fractionation of stable carbon and oxygen (δ13C and δ18O) as well as stable Ca isotopes (δ44Ca) during formation of (speleothem) calcite between all involved species: gaseous CO2, H2O, dissolved inorganic carbon (DIC) and directly precipitated CaCO3. Our novel experimental set up allows to simulate the soil and karst above the cave (dissolution of CaCO3) as well as the cave system (precipitation of CaCO3). During the experiments, the pCO2 of the atmosphere, relative humidity, temperature, dissolved CO2, pH, electrical conductivity as well as the δ13C and δ18O values of the gaseous CO2 and the DIC are monitored in-situ. The δ13C and δ18O values are measured using a state of the art isotope ratio infrared spectrometer (DeltaRayTM by Thermo Fisher ScientificTM), which is directly coupled to the experimental system. This allows to reproduce identical solutions for all experiments and to keep the experimental conditions stable. During the experiments, the solution is caused to flow down inclined glass plates as thin solution film (ca. 0.1 mm) precipitating CaCO3 along the flow path. After different distances of flow and thus residence times on the plates, pH, remaining Ca2+ as well as the isotope composition of both the DIC and the directly precipitated CaCO3 are measured. This enables to directly determine the Ca-, C- and O-isotope fractionation between all involved species in the system (CO2, H2O, DIC and CaCO3) with respect to various parameters, such as different temperatures, pCO2, initial super saturation as well as precipitation rate. The combination of traditional and non-traditional stable isotope systems might provide a powerful toolbox in order to improve the interpretation of speleothem paleoclimate records in terms of correction for disequilibrium isotope effects. With our set-up, we ultimately aim for a more quantitative understanding of isotope fractionation processes during formation of speleothem calcite at a so far not achieved precision.
SEDIMENTARY GEOLOGY, PALEOCLIMATE AND ENVIRONMENTAL CHANGEINVESTIGATION OF THE SOIL-KARST SYSTEM THROUGH A MOCK-UP TEST: CO2 VARIATION UNDER CONTROLLED ENVIRONMENTAL CONDITIONS
1Unidad de Hidrogeociencias Ambientales, Dpto. de Medioambiente, CIEMAT, Madrid, 28040, Spain; 2Fundación Atapuerca-CENIEH, Paseo Sierra de Atapuerca, 3, 09002 Burgos, España; 3Dpto. de Geodinámica, Estratigrafía y Paleontología. Facultad de CC. Geológicas, Universidad Complutense de Madrid, Madrid, 28040, Spain
One small-scale mock-up test was carried out with a layer of ground limestone covered by a layer of soil. Limestone and soil come from Ojo Guareña National Monument, a karstic complex located in the north of Spain, in which we have had an active monitoring program for 20 years. With the test we intend to obtain information on the variation of CO2 in controlled environmental conditions and to have a reliable database to calibrate numerical models and a better understanding of the key parameters that influence the evolution of CO2.
The mock-up consists on a chamber that has an area of 40 cm x 36 cm at the base and 60 cm in height. The limestone occupies the lower part of the chamber and is covered by a thin layer of soil with herbaceous plants that have grown spontaneously from the seeds contained in the soil itself. Four artificial cavities have been simulated in the limestone at four different heights from the base of the chamber (10, 20, 35 and 50 cm). Data collection of air carbon dioxide concentration, air temperature, relative air humidity, atmospheric pressure and TVOC is performed at those four cavities, in addition to monitoring atmospheric and exhalation parameters. The equipment used for measuring was designed and assembled by ourselves from commercial components. Inner cavities consist on small compact boxes that include a commercial CJMCU-8128 sensor module. In those cases when exhalation and atmospheric measurements are determined, commercial MHZ-19 sensors were used. In all the cases, the signal of the sensors is processed by a microprocessor (ESP32-WROOM) and converted into a digital output to a numeric value. Measurements can be made with periodicity ranging from seconds to hours.
The test was launched in November 2021. Rainfall is simulated by irrigating once a week with 1000 mL of rainwater collected in the Ojo Guareña Natural Monument. Data logging is done automatically every 15 minutes. Air is periodically extracted from the cavities to measure CO2 and δ13C with a CDRS Picarro CO2 isotope analyser. Water samples are also taken periodically at different points to analyse major elements and stable isotopes. First data indicates that ground limestone has a high reactivity and there is an increasing of CO2 from the surface towards the bottom, with large amounts of CO2 stored at the bottom of the mock-up chamber (several thousand of ppm ). However, a 25% of CO2 is flushed out by exhalation.
Contribution to Project CGL2017-83287-R (MICINN, Spain) and to research group ‘‘Sedimentary Geology, Paleoclimate and Environmental Change’’ (UCM, Spain).
Analysis of stalagmites collected from the human-occupied caves beneath Mayapán, the political and cultural capital of the Postclassic Maya
1Department of Earth Sciences, University of Cambridge, United Kingdom; 2Department of Geography and Environmental Sciences, Univerty of Northumbria, United Kingdom; 3Deparment of Earth Sciences, University of Durham, United Kingdom; 4Department of Geological Sciences, University of Florida, USA; 5Department of Anthropology, University of California, Santa Barbara, USA
Mayapán emerged as a regional Postclassic Maya capital on the Yucatán Peninsula (modern Mexico) between 1000 and 1100 cal. CE. Rapid nucleation of population occurred ~1200 cal. CE, and a dense city population continued until 1320 cal. CE. After a series of political and military events, the state declined and the city was abandoned after 1450 cal. CE (Kennett et al., in review). At its peak, an estimated 15,000–17,000 people lived in or around the Mayapán 4.2 km2 urban zone. The Yucatán Peninsula is a karstic limestone shelf, and the only water sources within Mayapán’s city wall were collapsed dolines that intersected the water table and cave chambers that held pools of water. Archaeologists have documented as many as 40 cenotes (sinkholes) within Mayapán’s city wall (Brown 2005; 2006). Caves and cenotes were ritually and religiously associated with lineages at the city of Mayapán (Brown, 2005).
We have collected five small stalagmites from Cenote Ch’en Mul, with permission granted by Mexico’s Instituto Nacional de Antropología e Historia (INAH). One chamber of the cave extends beneath the city’s central pyramid, the Temple of Kukulcán. The cave beneath the temple probably had mythical significance for the Maya (Brown, 2005); ceramics and evidence of historic human activity were found within the cave, and some Mayapán buildings were ornamented with stalagmites from the caves.
Analysis of the Cenote Ch’en Mul stalagmites are presented here to stimulate discussion about how the samples’ geochemical features (stable isotope ratios, element concentrations) and visible features (layer coloring, crystal structure) can be interpreted within an archaeological context. One stalagmite, collected 20 m from the cave entrance, grew from ca. 1020 to 1410 cal. CE, almost the entire period when Mayapán was densely occupied. The calcite is dark and ‘dirty,’ and contains several detrital layers. Clear fluorescent laminae along with multiple U-Th anchor points constrain the age model to a 30-year 95% confidence interval around a growth hiatus at 1410 cal. CE. The growth hiatus occurred just a few decades prior to the Mayapán political and demographic collapse (1441-1461 cal. CE), which may have occurred in the context of drought and internal conflict (Kennett et al., in review). The stalagmite began to grow again around 1600 cal. CE, long after the city had been abandoned, and this growth was in the form of clean, white, unlaminated aragonite. The results from this stalagmite are compared with the results from a handful of stalagmites collected from deeper within the cave, some of which share similar face features, but possess there own unique geochemical variations.
Brown, C.T. Caves, karst, and settlement at Mayapán, Yucatán. In the maw of the earth monster: Mesoamerican ritual cave use 373–402 (2005).
Brown, C.T. Water sources at Mayapán, Yucatán, Mexico, in Precolumbian. Water Management: Ideology, Ritual, and Politics 171–85 (2006).
Kennett, D.J. et al., Drought-Induced Civil Conflict Among the Ancient Maya, in review at Nature Communications.
Collapse of the Liangzhu and other Neolithic cultures in the lower Yangtze region in response to climate change
1Institute of Global Environmental Change, Xi’an Jiaotong University, Xi’an 710054, China; 2State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China; 3Key Laboratory of Karst Dynamics, Ministry of Land and Resources, Institute of Karst Geology, Chinese Academy of Geological Sciences, 541004 Guilin, China; 4California State University Dominguez Hills, Carson, CA 90747, USA; 5Institute of Geology, University of Innsbruck, Innsbruck 6020, Austria; 6School of Art and Archaeology, Zhejiang University, Hangzhou 310028, China; 7Department of Earth Sciences, Uni- versity of Minnesota, Minneapolis, MN 55455, USA.
The Liangzhu culture in the Yangtze River Delta (YRD) was among the world’s most advanced Neolithic cultures. Archeological evidence suggests that the Liangzhu ancient city was abandoned, and the culture collapsed at ~4300 years ago. Here, we present speleothem records from southeastern China in conjunction with other paleo- climatic and archeological data to show that the Liangzhu culture collapsed within a short and anomalously wet period between 4345 ± 32 and 4324 ± 30 years ago, supporting the hypothesis that the city was abandoned after large-scale flooding and inundation. We further show that the demise of Neolithic cultures in the YRD occurred within an extended period of aridity that started at ~4000 ± 45 years ago. We suggest that the major hydrocli- matic changes between 4300 and 3000 years ago may have resulted from an increasing frequency of the El Niño– Southern Oscillation in the context of weakened Northern Hemisphere summer insolation.
Comparison of climate and environment on the South African south coast to the Little Karoo in Marine Isotope Stages 5 – 2 as indicated by speleothems
1Arizona State University, United States of America; 2Geological Survey of Israel; 3Hebrew University of Jerusalem, Israel; 4Nelson Mandela University, South Africa; 5Universidade do Algarve, Portugal; 6La Trobe University, Australia; 7University of Johannesburg, South Africa
The South African south coast is a key location for the evolution of modern humans and advancements in complex behavioural and cultural patterns. It also hosts a highly diverse and unique floral ecosystem. Given the steep present-day climatic gradients in southern South Africa, comparative studies of its coastal and inland paleoclimate provide important paleoenvironmental and paleoclimatic context to hunter-gatherer resource availability and vegetation dynamics.
We present a comparative study of speleothem stable oxygen (δ18O) and carbon (δ13C) isotopic composition from Efflux Cave (113 - 19 ka, hiatus between 105 and 94 ka) in the Little Karoo inland basin and Sandkraal Cave (120 - 9 ka) on the present-day south coast. Due to the wide continental shelf, Sandkraal Cave would have been located at the boundary between the Cape coastal lowlands (a narrow foreland of the 1000-1500m high Outeniqua Mountain range) and the Paleo-Agulhas Plain on the currently flooded shelf. Human occupation is evident in rock shelters near both speleothem locations, but it is unclear whether the occupants of the two regions would have encountered similar food resources and consistent water sources.
Gaussian kernel based cross-correlation analyses against other paleoclimate proxy records show that rainfall seasonality at Efflux Cave is related to rainfall amount in the South African interior. At Sandkraal Cave correlations are higher with records from the South African east coast probably related to influences of the Agulhas Current.
Cross-correlation analyses of the records from Efflux Cave and Sandkraal Cave compared to previously published speleothem records from southern Africa show only limited statistical correlation. However, there are some similarities in overall trends of paleoclimate change in the Cape coastal lowlands and the Little Karoo whereby Marine Isotope Stage (MIS) 5b (mainly Greenland Interstadial 22) and 4 generally have more summer rainfall and higher abundances of C4 vegetation than MIS 5a and MIS 3.
The speleothem records, corroborated by archaeological evidence from the coastal and inland areas, suggest that in both regions surface water was readily available and grassland ecosystems with variable amounts of C4 and C3 grasses as well as fynbos communities could be found nearby.
Middle MIS 3 multi-proxy study of a speleothem from Bloukrantz cave, South Africa
1Department of Earth Sciences and Bjerknes Center for Climate Research, Bergen, Norway; 2SFF Centre for Early Sapiens Behaviour (SapienCE), University of Bergen, Bergen, Norway; 3Department of Earth Sciences, Bergen, Norway; 4Andalusian Earth Sciences Institute, University of Granada, Granada, Spain; 5Department of Anthropology and Archaeology, University of South Africa, Pretoria, South Africa; 6Department of Environmental Sciences, University of Basel, Basel, Switzerland; 7Climate and Environmental Physics Division, Physics Institute and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
<p>Current archeological evidences highlight the 100-50 ka period as being a watershed for human cognitive, technological and social development in Africa. High-resolution climatic and environmental records are needed to provide context for the behavioral evolution of early <em>Homo sapiens</em>. Here we present trace element and stable isotope data along with temperature reconstructions from both fluid inclusion microthermometry and fluid inclusion water isotopes from a speleothem (BL3) collected in Bloukrantz Cave, in the De Hoop Nature Reserve in the Western Cape region of South Africa.</p>
<p>BL3 grew from 48.3 to 45.2 ka and from 7.6 to 1.6 ka. Here we focus mainly on the older part of BL3 (during Marine Isotope Stage -MIS 3), where both 𝛿<sup>18</sup>O<sub>c</sub> and 𝛿 <sup>13</sup>C<sub>c</sub> vary strongly, and covary with Sr/Ca. This correlation suggests that the control on the proxies originates from internal cave processes such as Prior Calcite Precipitation, which could be related to precipitation amount. The hydroclimate indicators furthermore suggest a shift towards overall drier conditions after 46 ka, coincident with cooling in Antarctica.</p>
<p>The temperature reconstructions show good agreement between both methods and display little variation throughout the record, with reconstructed temperatures close to the present-day cave temperature of 17.5 deg C. Overall, the BL3 record thus suggests stable temperature from 48.3 to 45.2 ka whereas precipitation was variable with marked drier episodes on sub-millennial timescale. Future studies will extend the record back in time to investigate whether this type of hydroclimate variability might have affected the early humans in the region.</p>
Preliminary 230Th/U-dating of speleothems from southern Greece and their potential in climate archeology
1Landesmuseum für Kärnten, Klagenfurt am Wörthersee, Austria; 2Institute for Geosciences, Johannes Gutenberg-University, Mainz, Germany; 3Deutsches Archäologisches Institut, Athens, Greece
Modern climate in southern Greece displays a strong seasonality with warm and dry summer months and cool and humid winter months. This limits the water availability for agriculture and also influenced the migration of ancient cultures.
During a field campaign in 2020 several speleothems were collected from eight caves in Greece. The scope of the campaign was to study the implications of climate history and the cultural progress and ancient settlements.
Here we present the first preliminary results of 230Th/U-dating of speleothems from the Peloponnese, Central Greece, Attica and the Island of Samos. The collected speleothems show a high variety in ages covering the last 300 ka, and one sample from Ambouria Cave is even beyond the limit of the 230Th/U-dating method. Apart from Holocene samples, preferential speleothem growth is observed during interglacials and Dansgaard/Oeschger interstadials. The youngest samples with ages of up to a few thousand years with archeological context are difficult to date with the 230Th/U-dating method, due to the low U content and the relatively high amount of detrital Th. Nevertheless, the speleothems in total show the huge potential for paleoclimate reconstruction of the last 300 ka and complement the existing pollen archives.
Especially for Island of Samos, we present the first data of a potential palaeoclimate archive from the Pleistocene. 230Th/U ages of speleothems show the potential for high-resolution palaeoclimate reconstruction of the end of MIS 5, including Dansgaard/Oeschger events 20 to 18, and probably for MIS 8.
The region of the ancient Lake Kopais in Boeotia is well known for the first artificial irrigation in history. 230Th/U-dating of speleothems from Trabala Cave display Holocene ages, which is in agreement with archeological finds. However, due to the degree of detrital contamination, precise dating is challenging, and accurate chronologies are difficult to construct. Holocene samples from Attica focusing the same difficulties regarding the detrital contamination.
The spatiotemporal extent of the Green Sahara: Consequences for pre-historic human populations
1Mohammed VI Polytechnic University, Morocco; 2Xi'an Jiaotong University, China; 3IBS Center for Climate Physics, South Korea; 4Xi'an Jiaotong University, China; 5Ibn Zohr University, Morocco; 6University of Sao Paulo, Brazil
The Sahara Desert, one of today’s most inhospitable environments, has known periods of enhanced precipitation that supported pre-historic humans. However, the Green Sahara timing and moisture sources are not well-known due to the scarcity of paleoclimate information. Here, we present a multi-proxy (δ18O, δ13C, Δ17O, and trace elements) speleothem-based climate record from NW Africa. Our data document two Green Sahara periods during MIS5a and the Early to Mid-Holocene. The consistency with paleoclimate records across North Africa highlights the east-west geographical extent of the Green Sahara, whereas millennial-scale North Atlantic cooling events consistently resulted in drier conditions. We demonstrate that an increase in westerly-originating winter precipitation during MIS5a resulted in favourable environmental conditions for the survival of human populations. The abrupt climate deterioration and the decline in human density in the Sahara during the MIS5-4 transition suggest climate-forced dispersals of local populations, with potential implications for migration pathways out of Africa.
U-SERIES AGE CONSTRAINTS FOR CAVE ART IN CUEVAS DE PUENTE VIESGO (CANTABRIA, SPAIN) - MINIMUM AGES FOR PAINTINGS IN EL CASTILLO AND LA PASIEGA
1University of Göttingen, Germany; 2Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany; 3University of Southampton, Southampton, UK; 4Complutense University of Madrid, Madrid, Spain; 5Durham University, Durham, UK; 6ICREA, Barcelona, Spain; 7University of Barcelona, Barcelona, Spain; 8Universidade de Lisboa, Lisboa, Portugal
Cave art is found on almost every continent and, in addition to its bearing on the origins of art itself, it constitutes an important source of archaeological information about symbolic behaviour of early human groups. Accurate chronological control of the emergence and/or execution of cave art is important for its interpretation, but cave art has proven to be one of the most difficult archaeological phenomena to date.
U-series dating is a well established geochronological tool for speleothems in palaeoclimatic research. However, its potential to provide age constraints for archaeological sites or artefacts in cave environments has not yet been fully exploited. We present U-series analyses on calcite crusts that formed on top of cave paintings. Recent developments in multi-collector (MC) inductively coupled plasma mass spectrometry (ICPMS) U-series dating greatly improved the precision of this method, and sample sizes needed to obtain reliable results were significantly reduced. Based on these developments the U-series technique can be applied for accurate dating of thin calcite crusts covering cave art at many sites, while taking care not to harm the art underneath. The method provides minimum ages for the covered art and, where possible, also maximum ages by dating the flowstone layer the art is painted on. We present results for El Castillo and La Pasiega, two important caves of Puente Viesgo in Cantabria, Spain, including one the oldest known cave paintings to date.
A 120-year seasonally resolved speleothem record of precipitation seasonality from southeastern China
1xi'an Jiaotong University, China, People's Republic of China; 2Institute of Mountain Resources, Guizhou Academy of Sciences, Guiyang, China; 3State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China; 4Department of Earth Sciences, University of Minnesota, Minneapolis, USA; 5Key Laboratory of Karst Dynamics, MLR, Institute of Karst Geology, CAGS, Guilin, China
Speleothem oxygen isotope (d18Os) record as a climatic proxy in southeastern China is still in debate due to multifaceted influencing factors, a modern d18Os record, which can be calibrated or compared with observational data, is critical to explore the interpretation of d18Os proxy. Here we present a seasonally resolved d18Os record spanning the interval of 1898-2018 CE from Niubi Cave, Guangdong Province, southeastern China. A comparison between the Niubi d18Os and instrumental data reveals that the Niubi d18Os variability is primarily controlled by changes in precipitation seasonality modulated by El Nino Southern Oscillation on interannual to interdecadal timescales. Higher (lower) d18Os values correspond to lower (higher) ratios of the East Asian summer monsoon/non-summer monsoon precipitation during the El Nino (La Nina) events associated with concomitant changes in the outgoing longwave radiation, wind field and Western Pacific Subtropical High. While ~73% historical drought events correlate to positive anomalies in Niubi d18Os values over the last 120 years, the rest of drought events associate with the negative d 18 O s anomalies. This observation suggests two different mechanisms for the drought events with more and less diminution of rainfall amount in the East Asian summer monsoon relative to the non-summer monsoon precipitation, respectively. Additionally, our Niubi d18Os record from southeastern China, together with other high-resolution speleothem and tree ring records, demonstrate a “tripole pattern” of summer precipitation during the last ~100 years in eastern China.
A new modelling approach for extracting palaeoseasonality from lower resolution stalagmite proxy records
1Durham University, UK; 2University of Bern, Switzerland; 3Northumbria University, UK; 4Teesside University, UK; 5Lancaster University, UK; 6University of Leeds, UK; 7University of Reading, UK; 8Federal Office for Radiation Protection, Germany
Over recent decades, stalagmites have progressed to the forefront of terrestrial palaeoclimate archives due to their amenability to high precision age dating, their widespread distribution, and their capacity to record seasonal-to-decadal scale climate and environmental information (1). Although recent advances in analytical techniques and computerised micromilling of stalagmites for oxygen and carbon isotopes allow for extraction of monthly to seasonal palaeoclimate information (e.g.,2-5), there are hundreds of lower resolution stalagmite records in the SISAL database (6,7,8) with the untapped potential to yield seasonal climate information.
Here we present a new modelling technique for extracting meteoric precipitation amount and temperature palaeoseasonality from lower-than-seasonally resolved stalagmite d18O data (1,9). The modelling approach provides a more detailed view of climate change compared to a semi-quantitative discussion of stalagmite d18O in terms of shifting rainfall budget on annual or longer timescales. Instead, our model assesses the role of seasonality in driving the observed d18O variations. Intervals where a model does not converge could highlight climate anomalies forced by other factors not included in the model. Application of similar approaches in future stalagmite-based palaeoclimate research could deepen our understanding of natural and anthropogenic drivers of rainfall dynamics and temperature on seasonal timescales.
1. Baldini, J.U.L. et al. (2021) QSR 254, 106784; 2. Carlson, P.E. et al. (2018) Geochem. Cosmochim. Acta 235, 55e75; 3. Orland, I.J. et al. (2019) Proc. Natl. Acad. Sci. 116, 24985e24990; 4. Ridley, H.E. et al. (2015) Nat.Geosci. 8, 195-200; 5. Orland, I.J. et al. (2015) Geology 43, 555e558; 6. Comas-Bru, L. et al. (2020) Earth Syst. Sci. Data 12(4), 2579—2606; 7. Comas-Bru, L., et al. (2019) Clim. Past, 15, 1557–1579; 8. Atsawawaranunt, K., et al. (2018) Earth Syst. Sci. Data, 10, 1687–1713; 9. Baldini, L.M. et al. (2019) QSR 226, 1-22.
CAVES AS SENTINEL SITES IN THE WESTERN-MEDITERRANEAN REGION: HYDROCLIMATE VARIABILITY DURING THE LAST 2700 YEARS
1GRC Geociències Marines, Departament de Dinàmica de la Terra i de l’Oceà, Facultat de Ciències de la Terra, Universitat de Barcelona, Barcelona, Spain; 2Centre for Climate Change (C3), Dept. of Geography, Universitat Rovira i Virgili, 43480, Vila-seca, Spain.; 3Departamento de Procesos Geoambientales y Cambio Global, Instituto Pirenaico de Ecología – CSIC, Zaragoza, Spain; 4Department of Earth Sciences, ETH Zürich, Switzerland; 5Department of History and Archaeology, Universitat de Barcelona, Barcelona, Spain; 6Department of Earth and Environmental Sciences, University of Minnesota, MN 55455, USA; 7Institute of Global Environmental Change, Xian Jiaotong University, Xian 710049, China; 8Grup de Recerca en Ciències de la Terra, Universitat de les Illes Balears, Mallorca, Spain
According to the current climate change situation, the Mediterranean region has been identified as one of the primary hot-spots, expecting not only to become warmer, but also drier during the twenty-first century. This trend is already confirmed by recent decades of observations from the Balearic Islands, for which rates of warming and precipitation reduction were even higher than those expected from the currently available climate predictions. In addition, these changing conditions also include an increase in the frequency of intense Mediterranean torrential rainfall events, whose occurrence has already caused increasing flash flood events with catastrophic impacts and human casualties such as those during autumn 2018 in Mallorca Island.
Here we present two examples of the potential of caves as sentinels of hydroclimate variability of the past. On the one hand, the precipitation variability of the last 2700 years has been reconstructed applying a multi-proxy methodology on five stalagmites from two caves of Mallorca Island. The mean time resolution of the records ranges between 2 and 7.6 years considering a stalagmite sampling resolution of 1 mm. Environmental parameters of one of the caves have been monitored for 5 years. None of the studied stalagmites cover the whole 2.7 kyr period but they provide sufficient overlap to replicate most of the discussed climatic intervals with the exception of the Medieval Climate Anomaly (MCA; 900-1275 yr CE) and earliest part of the Little Ice Age (LIA; 1275-1850 yr CE), which is represented by a hiatus. Taking into account the results of five years farmed calcite samples collected on glass plates and cave environmental parameters, the stalagmite δ18O record is interpreted to reflect mostly prior calcite precipitation (PCP) changes that respond to hydrological changes in the region. A principal component analysis has been applied to the stalagmite geochemical data set and a composite δ18O record to obtain a robust regional hydrological record. This record indicates that generally wet conditions dominated for the Talaiotic Period (TP; until 123 yr BCE) and the early Roman Period (RP; 123 yr BCE-470 yr CE), the first half of the Early Middle Ages (EMA; 470-900 yr CE) and the second part of the LIA, while dry conditions characterized the late RP, the late EMA and the entire MCA.
On the other hand, past extreme rain events have been reconstructed in Mallorca from the observation of particular morphological features in stalagmites, which are in agreement with data from historical documentary sources. Finally, this paleohydrological data is compared with paleoceanographic data of the same study area in order to better understand the interactions between atmosphere-surface and deep-sea, and the operation of the climate system from a multidisciplinary perspective. The ocean-atmosphere approach suggests complex non-stationary climate patterns for the last 2.7 kyr, including the occurrence of both wet-warm and wet-cold intervals and an underlying complex interplay of factors controlling climate evolution in the region.
Detecting multiannual to multidecadal precipitation variability in a speleothem from Mona Island, Puerto Rico
1Department of Earth and Environmental Systems, Indiana State University, Terre Haute, IN, USA; 2Department of Geoscience, University of Nevada, Las Vegas, USA; 3Institute of Environmental Physics, Heidelberg University, Germany; 4Institute of Earth Sciences, Heidelberg University, Germany; 5Xi'an Jiaotong University, Xi’an, China
Existing precipitation records from the Eastern Caribbean from multiple archives reveal heterogenous patterns attributed to the placement/shifting of the ITCZ through time and the complex oceanic/atmospheric interactions/teleconnections of ENSO, NAO, and AMO. This region is also characterized by its proximity to the AMOC system and the main development region of tropical cyclones. On shorter decadal time scales, climate variability has been attributed to volcanic and solar forcings.
Here we present carbon and oxygen stable isotope timeseries of MO-AL-3, a speleothem from Cueva del Aleman Mona Island, Puerto Rico. U-Th dating reveals that the record spans 500 to 80 yrs BP, allowing the investigation of multiannual to multidecadal precipitation variability, as well as linkage to past human activity. The study of precise, independent chronologies extracted from speleothems, and comparing them to local and regional SST and past tropical cyclone reconstructions from other proxies such as sediment records, corals and sclerosponges allow for an improved understanding of precipitation patterns of the Northeastern Caribbean over time and their connection to climate modes characterizing the area. Preliminary timeseries analysis reveals multiannual to multidecadal variability which could be attributed to internal oscillations like ENSO or the NAO. Analysis also reveals an 11-year period that could coincide with the sunspot cycle, pointing toward the influence of solar cycles.
Early Anthropogenic Impacts on the Indian Summer Monsoon Induced by Land-use and Land-cover Changes
1Earth Observatory of Singapore and Asian School of the Environment, Nanyang Technological University; 2Department of Geosciences, National Taiwan University; 3Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences; 4State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences; 5College of Geography Science, Nanjing Normal University; 6Research Center for Environmental Changes, Academia Sinica,
The impacts of anthropogenic forcing on Indian summer monsoon (ISM) rainfall are obscure, partly due to limited availability of highly resolved hydroclimate proxy records as well as the highly regionalized nature of precipitation. Here, we report an annually-resolved speleothem oxygen isotope record from Xianren Cave, southwestern China, which represents rainfall change over the broad ISM region. We find that the region has endured at least six decadal-scale droughts in the past three hundred years. One of them, lasting from the early to mid 19th century, shares the similar gradual, persistent trend as the most recent decline in ISM rainfall and both have a magnitude substantially larger than the others dominated by natural variability. This early megadrought occurred during a historical time of intensive deforestation in the region. We conclude that the ISM trend could have been altered by the changes in land-use and land-cover since the early 19th century.
IN-SITU TRACE ELEMENT ANALYSES OF A SPELEOTHEM FROM THE TROPICS TO TRACK PALEOFLOOD EVENTS THROUGH THE HOLOCENE
1Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, 02912, U.S.A; 2Institute at Brown for Environment and Society, Brown University, Providence, 02912, U.S.A; 3Instute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, 78712, U.S.A
Hydroclimate extremes such as floods have far reaching impacts on tropical island nations. The hydrological cause of floods is linked to local intense storms, a result of climate dynamic systems such as the monsoon season or phases of the El Niño Southern Oscillation. The Philippines is one such tropical island nation nestled near the Western Pacific Warm Pool in the Pacific Ocean that is impacted by flood events. Climate change is expected to exacerbate the intensity of flooding events in these tropical islands towards the end of the 21st century. Instrumental records of floods using either gauge stations or satellite data are temporally limited to no more than 50 years. However, geological indicators of paleofloods can help discern the variability in flooding events and provide insight into the climate dynamic systems causing the events.
Here, we present in-situ Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) trace element analyses of a speleothem sample, SR-02, collected from the Puerto Princesa Subterranean River National Park in Palawan, Philippines (10.2°N, 118.9°E). Through U-series dating, SR-02, continuously grew between 14 kyr and 6 kyr before entering a hiatus. Therefore, we focus our trace element analyses over this time period. Investigating the variability in transition metal (Fe, Cu, Zn, Mn, Co, Ni), which are associated with transport of labile solute matter during flushing event, concentrations will provide insight into the paleoflood history for the Philippines. Variable cyclicity in the alkaline-earth (Mg, Ba, Sr) trace metals will further be analyzed to investigate local epikarst hydrological processes such as prior calcite precipitation.
LOCAL CLIMATE VARIABILITY OF THE LAST 600 YEARS RECORDED IN A SPELEOTHEM FROM THE NORTHERN YUCATAN PENINSULA
1Institute of Environmental Physics, Heidelberg University, Heidelberg, 69120, Germany; 2Institute of Earth Science, Heidelberg University, Heidelberg, 69120, Germany; 3Department Earth Sciences, Khalifa University, Abu Dhabi, 127788, UAE; 4Instituto de la Prehistoria de América, Solidaridad 77711, Quintana Roo, Mexico; 5Museo del Desierto, Saltillo 25022, Coahuila, Mexico; 6Universidad Nacional Autónoma de México (UNAM), Campus Yucatán, Mexico; 7Grupo Espeleológico Ajau, Merida, Yucatan, Mexico
Speleothems provide unique archives to reconstruct past changes in precipitation over the climate-sensitive region of the northern Yucatán Peninsula. Strong spatial and temporal gradients are visible in this region due to the position of the Intertropical convergence Zone (ITCZ), although this is not the only driver of hydroclimatic variability in the region.
Here, we present a nearly annual-resolution trace element and stable isotope record from Áaktun Kóopo cave, Estrella, near Valladolid on the northern Yucatán Peninsula. High-precision 230Th/U ages show that the three analyzed stalagmites E0-C, E1 and E8 cover the last 1400 years nearly continuously.
In particular, stalagmite E1 grew during the last 600 years, showing only one growth hiatus of a few years to decades between c. 1860 and 1940 AD. The stable isotope record (δ18O and δ13C) has an average temporal resolution of 1–2 years per sample, while the LA-ICP-MS trace element record reaches even sub-annual resolution.
Both, trace element ratios (Mg/Ca, Sr/Ca, etc.) and stable isotope values (δ18O, δ13C) show pronounced variability on the inter-annual to decadal scale. A continuous increase in Mg/Ca ratio towards the hiatus, suggests that this growth stop may be the result of a steady decrease in precipitation/recharge, and hence more arid climatic conditions. A contemporaneous increase of δ18O and δ13C values during that period supports this assumption.
Ongoing work on other stalagmites from the same cave will partly replicate and expand the high resolution paleoenvironmental record from Áaktun Kóopo cave. The comparison of our results with other regional climate reconstructions as well as historic records will further improve the understanding of the driving mechanisms of past regional climatic changes and potential societal impacts.
PERSISTENT LONG-TERM DROUGHT CAPTURED IN SOUTHERN AMERICAN SPELEOTHEM
1Federal Fluminense University, Brazil; 2Universidade Estadual de Goias (UEG), Iporá-GO, Brazil; 3Instituto de Geociências, Universidade de São Paulo (USP), São Paulo-SP, Brazil; 4Centro de Geociencias, Universidad Nacional Autónoma de México, Campus UNAM, Juriquilla, Querétaro, México; 5Department of Atmospheric and Environmental Sciences, University at Albany, State University of New York, Albany, NY, USA; 6Center for Earth System Science (CCST), National Institute for Space Research (INPE), São José dos Campos, Brazil; 7Institute of Global Environmental Change, Xi'an Jiaotong University, Xi'an, China; 8Instituto Federal de Educação, Ciência e Tecnologia do Norte de Minas Gerais, Januária, Brazil; 9Instituto Geofísico del Perú, Lima, Peru; 10Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, United States; 11Department of Earth Sciences, University of Minnesota, Minneapolis, MN 55455; 12Department of Atmospheric and Environmental Sciences, University at Albany, State University of New York, Albany, NY, USA
The effects of global warming in fresh water resources are usually tied to changes in the mean annual rainfall. However, the increasing trend in temperature may also lead to a deficit in meteoric water recharge because it induces high evaporation. Such effect may have a great impact in the regional hydrologic balance (precipitation-evaporation) impacting regional-scale streamflow and groundwater availability. This process is particularly relevant for central Brazil, where a warming trend, significantly above the global mean, is observed in the last decades.
In order to reconstruct the effects of local changes in hydrologic parameters tied to rainfall and evapotranspirative demand we produced a seasonal-resolved oxygen isotope and trace element record in a well-ventilated cave located in central Brazil. Cave monitoring results show a consistent coupling between seasonal variation in trace elements and oxygen isotope composition from speleothem calcite and the cave atmosphere relative humidity and temperature. As a consequence, geochemical effects associated with periods of decreasing rainfall (higher δ18O values and Mg/Ca) are amplified by the increase in evaporation during dripping, leading to even higher δ18O and Mg/Ca values in the speleothems.
Instrumental records show a marked change in the hydrologic balance in central eastern Brazil, dragged by a severe warming trend since the 1980s, that is well reproduced in the isotope and trace element (Mg/Ca) composition. The Onça cave isotope record shows a trend to high δ18O and δ13C values that has no counterpart during the last 280 years. Similarly, variations in trace element like Mg/Ca, Sr/Ca and Ba/Ca presents a steep increasing trend, suggesting the prior calcite precipitation as the main driver of trace element composition. These results reinforce the premise of a severe long-term drought in the tropics of Southern Hemisphere associated with the anthropogenic warming.
RECHARGE VARIABILITY IN THE AUSTRALIAN ALPS: INSIGHTS FROM CAVE MONITORING AND MODERN (1922-2006 CE) STALAGMITE δ18O RECORDS
1ANSTO, Lucas Heights, 2234 NSW, Australia; 2Connected Waters Initiative, UNSW Sydney, Kensington 2052 NSW, Australia; 3Climate Geochemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany; 4School of Environmental and Life Science, University of Newcastle, Callaghan NSW 2308, Australia; 5Bioanalytical Mass Spectrometry Facility, Mark Wainwright Analytical Centre, UNSW Sydney; 6School of Geography, Earth and Atmospheric Sciences, University of Melbourne, Parkville VIC 3052, Australia
The Australian Alps provides 9600 gigalitres of water annually to Australia’s largest river system, the Murray-Darling Basin (MDB). High quality water flowing from the Australian Alps supports the 2.3 million people living in the Basin and is estimated to deliver $9.6 billion per year to the Australian economy through hydroelectric power generation and contributions to the agricultural and tourism industry. Stalagmite δ18O records from the Australian Alps can therefore provide context for understanding multi-year dry and wet periods in the MDB over the Common Era.
Here, we present the first modern high resolution stable oxygen isotope timeseries of three stalagmite records from Harrie Wood Cave that grew from 1922 to 2006 CE in the alpine region of southeast Australia. Harrie Wood Cave has been well-monitored for 10-years and we use extended surface and cave monitoring datasets, petrographic investigation, modelled recharge time series and farmed calcite precipitates to assess the controls on speleothem δ18O and investigate the coherence between three records from Harrie Wood Cave. The cave drip-water Cl, δ18O and drip rate displayed a clear response to an increase in rainfall recharge. Consequently, it is demonstrated that stalagmites from Harrie Wood cave also record variability in interannual recharge over the last 84-years. Isotopic fluctuations up to 1.1‰ recorded in the stalagmite δ18O record is in response to changes in recharge, where an increase in δ18O values close to, or higher than, the δ18O PWM is observed with lower recharge, while lower δ18O values than the δ18O PWM correspond to higher recharge amounts. Three stalagmites from within the Harrie Wood Cave system that grew over the same period were analysed and their reproducibility assessed. The three stalagmite δ18O records are in broad agreement, showing common responses to relatively higher recharge between 1945 and 1995 CE and the low recharge periods between 1937 and 1945 CE (World War II drought) and late 1996 to 2006 CE (beginning of the Millennium Drought). Based on evidence from our cave monitoring study and farmed calcites, we conclude that the differences in same-cave-stalagmite δ18O records are related to local karst hydrology i.e., variability in the contribution of preferential flows during recharge events and the store reservoir volume supplying the drip site.
The results from this research provide compelling evidence that stalagmite δ18O from Harrie Wood Cave, and likely other caves in the Australian alpine region, are sensitive archives of regional recharge and therefore provide direct insights on past variability in recharge. Finally, there is confidence that palaeo (pre-1900 CE) reconstructions from Harrie Wood Cave speleothem δ18O records will show sustained high-recharge years, but also extended drought periods (e.g., the Federation Drought, 1895 – 1902) which result in long-term variations in regional recharge.
Reconstructing land temperature variation from Pyrenean caves (N Spain) over the past 2,500 years
1Pyrenean Institute of Ecology, CSIC, Spain; 2Earth Sciences Department, University of Zaragoza, Zaragoza, Spain; 3Department of Stratigraphy, Paleontology and Marine Geosciences, Faculty of Geology, University of Barcelona, Barcelona, Spain; 4Geological Institute, Department of Earth Sciences, ETH Zurich, Switzerland; 5Stable Isotope Biogeochemistry Laboratory, IACT-CSIC, Armilla (Granada) Spain; 6School of Earth Sciences, The University of Melbourne, VIC 3010, Australia; 7Department of Earth Sciences, University of Minnesota, Minneapolis, USA; 8State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xian, China.; 9Institute of Global Environmental Change, Xian Jiaotong University, Xian, China
The Central Pyrenees is a high-altitude karstic region rich in cavities with active drips and present precipitation of carbonates. Although not generally very abundant, there are recent speleothems growths in several of those cavities. We present here the last 2500 years isotopic record resulting from compiling eight stalagmites from four different caves. In temperate regions such as the NE Iberian Peninsula is difficult to discern the influences on d18O variation in speleothems since temperature, amount of precipitation or even source effect are usually acting simultaneously (Moreno et al., 2014; 2021). Main results after ten years monitoring period indicate a strong dependence on air temperature through its influence on rainfall d18O, although a small amount effect is not discarded. The good overlapping during the observational period of d18O from actively growing modern stalagmites and air temperature in the area supports this dependence and provides a reliable proxy for the temperature evolution along last millennia.
The stalagmites belong to four different caves (Seso, Gloces, Pot au Feu and B-1 caves) and they have been dated combining U-Th and 14C (bomb peak) techniques. Their d18O profiles are very coherent in their main patterns allowing us to produce a stacked record with decadal resolution using Iscam software (Fohlmeister et al., 2012). Interpreting this signal as regional temperature variation divides the temporal sequence in five main periods, in consonance with historical stages. The less negative value of last 2500 years is reached at the most recent sample, after several decades of sharp increase, since ca 1870AD. The other clear - and in this case longer - warm interval is observed during the Roman Period (50BC-250AD). During the Dark Ages, there is no a positive interval, and almost the whole period remains in negative values. In fact, the most negative interval of last 2500 years is reached at ~550 years AD, a well-known cold period related to volcanic eruptions. Besides, the Medieval Climate Anomaly is characterized by two warm intervals (900-1000AD and 1150-1250AD) and during the Little Ice Age we found a long, cold interval (1250-1500AD, with two peaks specially negatives) Still, the most remarkable feature of the MCA and LIA periods is the large centennial-scale variability, showing both warm and cold intervals. In fact, the LIA has a clear three-partite pattern, with two negative periods at the onset and end and a positive interval in between. Contrarily, the MCA pattern, although also three-partite, it is characterized by two positive intervals at the onset and end and a short period of negative values in between.
This reconstruction is in striking similarity with other high-resolution records in Europe (Mangini et al., 2005) and, particularly, with global temperature reconstructions for last 2000 years (PAGES2k Consortium, 2013; Mann et al., 2008). In addition, the fact that the d18O signal presented here is so well replicated in speleothems from different caves gives strong support to our interpretation and opens the door to further research on Pyrenean speleothems as exceptional archives of thermal oscillations.
Revisiting the Meghalayan Age “Golden Spike”
1Xi'an Jiaotong University, Xi'an China.; 2Department of Earth Science, California State University Dominguez Hills, Carson, CA 90747, USA.
The abrupt positive oxygen isotope (d18O) excursion recorded in a single stalagmite (KM-A) from Mawmluh cave, Meghalaya in northeast India (Berkelhammer et al., 2012) was chosen by the International Union of Geological Sciences as the Global Stratotype Section and Point (GSSP) for the subdivision of the Holocene (the Meghalayan age, 4.2 ka to present) (Walker et al., 2018). However, the choice of this GSSP and whether the 4.2 ka event indeed manifested as a centennial-scale transient decline in the Indian summer monsoon (ISM) intensity, remain controversial (Michael et al., 2022). We have previously shown that two subsequent annually-resolved and well-dated d18O records from the Mawmluh cave failed to replicate the anomalous d18O signature of the KM-A record across the 4.2 ka event (Kathayat et al., 2018). In this presentation, I will present yet another δ18O record from Mawmluh cave, which is characterized by sub-annual temporal resolution and an average age uncertainty of 13 years constrained by 22 230Th dates. Our new data confirm our previous findings. Taken all together, now three well-replicated Mawmluh cave d18O records suggest that the KM-A stalagmite’s expression of the 4.2 ka event may be an outlier possibly due to its diagenetic alteration (Kathayat et al., 2018). In the long-term context of our data (last 4500 years ), the newer d18O records from Mawmluh cave suggest a possible “step-like” decrease at ~4000 ±50 years in the ISM strength rather than a precipitous “event-like” downturn. Our findings have major implications for understanding the role of climate in the de-urbanization phase of the Harrapan culture.
Berkelhammer, M., et al, An abrupt shift in the Indian monsoon 4000 years ago. Climates, Landscapes, and civilizations, (2012).
Kathayat, G., et. al., Timing and Structure of the 4.2 ka BP Event in the Indian Summer Monsoon Domain from an Annually-Resolved Speleothem Record from Northeast India. The climate of the Past (2018).
Kathayat G, et al., The Indian Monsoon Variability and Civilization Changes in the Indian Subcontinent. Science Advances (2017).
Marshall, Michael, DID A MEGA DROUGHT SEED GLOBAL CHAOS 4,200 YEARS AGO?: 498-501(2022).
Walker, M., et al., Formal ratification of the subdivision of the Holocene Series/Epoch (Quaternary System/Period): two new Global Boundary Stratotype Sections and Points (GSSPs) and three new stages/subseries. Episodes 41, no. 4 (2018).
Seasonality of precipitation recorded in a modern (1907-2008) annually laminated stalagmite from central China
Institute of Earth Environment, Chinese Academy of Sciences, China, People's Republic of
Seasonality of precipitation in the Asian monsoon region has significant impacts on social and economic development. Here, we analyzed a seasonally resolved δ18O series of an annually laminated stalagmite from Xianglong Cave to assess its potential as a proxy for seasonal precipitation. The δ18O values reveal fabric-correlated annual cycles, with lower δ18O values occurring in the white porous layer (WPL) during summer monsoon (SM) season, whereas higher values occurring in the dark compacted layer (DCL) during non-summer monsoon (NSM) season. We calculated the seasonal amplitude of δ18O (∆18O) using the highest value minus the lowest value in an annual cycle. Comparisons suggest that the ∆18O series can record precipitation seasonality, with lower ∆18O values corresponding to increased SM/NSM rainfall ratios and higher values corresponding to reduced SM/NSM rainfall ratios. Our reconstruction suggests increased precipitation seasonality contrast (i.e., increasing SM/NSM rainfall ratio with more SM rainfall and/or less NSM rainfall) during 1914-1919, 1935-1942, 1958-1962, 1979-1985, and 1999-2005 (A.D.), with a probably 27-year cycle. The seasonality of precipitation in central China correlates well with the Pacific Decadal Oscillation (PDO) on a decadal scale. Increased SM/NSM rainfall ratio was observed during the warm phase of PDO, and decreased SM/NSM rainfall ratio was observed during the cold phase of PDO.
Stalagmites as high-resolution archives of past fire severity
1UNSW Sydney, Australia; 2ANSTO, Australia; 3Australian Synchrotron ANSTO, Australia
Our understanding of fire regimes is largely limited to the satellite era. Being able to reconstruct past fire frequency and severity in the pre-satellite era, as well as climate pre-cursors, would greatly extend our knowledge of past fire regimes, and increase our understanding of ecosystem resilience and human relationships to fire. This knowledge would better inform how fire regimes might evolve with future climate change. Speleothems have recently been used to reconstruct past fire frequency for a site in southwest Australia (McDonough et al., 2022). Strong seasonality in the region produces speleothems with annual growth layers, enabling the timing of fire events to be precisely dated. Fire-sensitive proxies were found to include soluble ash-derived elements (mostly transition metals) and proxies which reflect changes in soil productivity, hydrology, and evapotranspiration (e.g. calcite δ18O, growth rate, organic matter and fabric). However, the response of these proxies differed between fire events, implying that the proxy response might also be related to fire intensity. A calibration study is required to further our understanding of speleothem-based fire records and assess whether fire intensity reconstruction is possible. Here we present findings towards a calibration of speleothems as fire severity archives for a site in southwest Australia. First, we determine if wildfire ash chemical composition varies with fire intensity. Then, we use synchrotron X-ray fluorescence microscopy elemental mapping to assess nine mini-cores from modern stalagmites known to have been actively growing during fires of differing intensities in 2019 and 2005 (with fire severity measured by satellite observations). Our results demonstrate clear differences in the composition of ash and the geochemical response of coeval stalagmites to known fires of differing intensities.
Using the modern speleothem record to understand the impacts of climate change on groundwater
1ANSTO, Australia; 2UNSW Sydney, Australia; 3University of Adelaide, Australia; 4Australian National University, Australia
Eight modern speleothem records from five caves in southwest Australia are examined. The temporal resolution of these records ranges from sub-annual to sub-decadal and six have chronologies based on laminae counting, permitting the largest replication study of speleothems across a region. The modern speleothems all show a consistent response to a sustained decrease in rainfall that began in the late 1960s, characterised by a pronounced increase or ’uptick’ in speleothem oxygen isotopic values (δ18O). Dripwater monitoring shows that the rising δ18O trend continues to the present. The magnitude of the uptick in the combined speleothem and drip δ18O record is 1.5 ‰, whereas we quantified that the change in rainfall mean δ18O values across the same interval were much smaller (-0.4 to +0.1 ‰; Griffiths et al., 2021). This rules out rainfall δ18O as responsible for the ‘uptick’ in the speleothem and drip dataset. We demonstrate that the decline in rainfall has reduced recharge along focussed flow paths resulting in a shift towards the diffuse flow end-member that has a higher δ18O value. Focused flow is also an important mechanism for rainfall recharge to groundwater, confirmed in our study by the isotopic agreement between focussed flow drips and Holocene groundwater δ18O values. Hence the cave ‘uptick’ provides an early warning signal that rainfall recharge to groundwater across this region is no longer reliably occurring due to climate change. Examination of the longer speleothem record shows that this is unprecedented over at least the last 800 years. This study also validates speleothems as recorders of past hydroclimate via amplification of the δ18O signal by karst hydrology (Treble et al., 2022) highlighting that speleothem δ18O are records of recharge, rather than a direct proxy for rainfall.
Griffiths, A.D., et al. (2022), Rainfall stable water isotope variability in coastal southwestern Western Australia and its relationship to climate on multiple timescales. Journal of Geophysical Research-Atmospheres, 127(1), e2021JD035433. doi:10.1029/2021JD035433.
Treble, P.C., et al. (2022), Ubiquitous karst hydrological control on speleothem oxygen isotope variability in a global study, Communications Earth & Environment, (1), 29. doi:10.1038/s43247-022-00347-3.
A doline sedimentary infill records a Pleistocene Black Sea level high stand at Mangalia, SE Romania
1Emil Racovita Institute of Speleology, Bucharest, Romania; 2Research Institute of the University of Bucharest, Bucharest, Romania; 3Callatis Museum of Archaeology, Mangalia, Romania; 4University of Bucharest, Faculty of Geology and Geophysics, Bucharest, Romania
We present here preliminary data from the study of a doline marine sedimentary infill on the Romanian Black Sea coast. To our knowledge this is the first marine deposit identified on the Romanian shore above the present day sea level and can bring valuable information about sea level change during Pliocene-Pleistocene environmental changes.
The doline is located 300 m inland, at ~10 m above the present day sea level. The sediment sequence was studied on a depth of 4 meters without reaching the base rock. It consists of a 1m thick marine clay unit rich in microcharcoal, overlain by other marine clays, marine sands, and a unit of anthropogenic infill.
The sediments contain marine microfauna such as the foraminifers Ammonia beccarii and Elphidium sp., as well as the ostracods Cyprideis littoralis, Amnicythere bacuana, A. multituberculata, Leptocythere sp., and Loxoconcha sp. Pollen, spores, and non-pollen palynomorphs were extracted from marine clays, although they are poorly preserved and in small quantity. The charcoal-rich marine clay layer contains relatively low concentrations of palynomorphs, with steppe-like taxa dominated by Chenopodiaceae together with Ericaceae at some levels, while arboreal taxa (Pinaceae, Cupressaceae, and Quercus sp.) are rare occurrences. Numerous coprophilous fungal spores (Sporormiella, Sordaria, and Arnium type) were also identified.
A pilot paleomagnetic study of two marine clay units revealed that they have a normal polarity. Given the presence of nearby loess deposits on the sea shore at a lower altitude than that of the doline, we argue that the doline could not have been submerged without these loess deposits being removed by erosion. As the deposition of these loess deposits started at the boundary between the Brunhes and Matuyama chrones, the normal polarity of the clay sediments implies the existence of at least two scenarios for the age of submergence. The doline was submerged either during the Brunhes chron and was uplifted by local tectonic processes, or it was submerged during an older period with normal polarity.
Detection of crystallinity changes in speleothem calcite and diagenetic oxygen isotope shifts in inclusion-hosted water
1Research Centre for Astronomy and Earth Sciences, Hungary; 2University of Newcastle, Australia; 3Institute of Biology, Eötvös Loránd University, Hungary; 4MTA-ELTE Geological, Geophysical and Space Sciences Research Group, Hungary; 5Department of Physical and Applied Geology, Eötvös Loránd University, Hungary
Stable hydrogen and oxygen isotope compositions of inclusion-hosted waters provide important tools to decipher past changes in temperature and hydrological conditions. In fact, they yield direct information on drip water isotopic composition without formation-related isotope fractionations. However, as the host calcite contain oxygen, late-stage calcite-water oxygen isotope exchange may result in values that do not reflect the the primary isotope record. Recrystallization-related oxygen isotope shifts in the inclusion-hosted water were documented in Demény et al. (2016a) at Baradla cave (Hungary). However, their finding may identify a peculiar, single occurrence. Nevertheless, new data about inclusion-hosted water compositions in speleothems suggest that such a diagenetic oxygen isotope shift can be a widespread phenomenon. This study presents the results from analyses of inclusion-hosted water composition in speleothems from three different locations: two cave systems in Hungary (Baradla and Vacska caves) and a cave in Atiu (Cook Islands Archipelago, South Pacific). The Hungarian locations has been monitored on a monthly basis in 2019-2021 (Czuppon et al., 2021), including sampling for microbial identification (Lange-Enyedi et al., 2022). By contrast, the remoteness of Atiu allowed obtaining water samples and farmed calcite only during two fieldwork expeditions (Faraji et al., 2021).
Speleothems collected from the three locations were investigated for stable isotope compositions of calcite and inclusion-hosted waters, as well as for XRD-based calcite domain sizes. All speleothems showed negative δ18O shifts with respect to local dripwater compositions. The δ18O shift is commonly negatively correlated with crystal domain size, although the starting composition and domain size is different for each individual deposits. As Enyedi et al. (2020) demonstrated, cave-dwelling bacteria can precipitate amorphous calcium carbonate (ACC) on the speleothem surface, which later crystallizes to nanocalcite (Demény et al., 2016a). As the ACC-H2O oxygen isotope fractionation differs from the calcite-H2O value, the trapped water changes the δ18O value to approach the new equilibrium (Demény et al., 2016b). The starting domain size may depend on the microbial carbonate’s characteristics as different caves can have different bacterial communities. The detection of coupled crystallinity and δ18O changes in far-away locations indicates that this early diagenetic process may be relatively common, regardless of the temperature of the cave.
The study is a part of the NANOCARB project (SA-41/2021) financially supported by the Eötvös Loránd Research Network.
Czuppon et al. (2021): doi: 10.1556/24.2021.00109
Demény et al. (2016a): doi: 10.1016/j.quaint.2015.11.137
Demény et al. (2016b): doi: 10.1038/srep39602
Enyedi et al. (2020): doi: 10.1038/s41598-020-65667-w
Faraji et al. (2021): doi: 10.1038/s41598-021-81941-x
Lange-Enyedi et al. (2022): doi: 10.1080/01490451.2021.201985
Hydrothermal silica dissolution and karst porosity formation in silicified carbonates: insights from Brazilian caves
1Department of Biological, Geological and Environmental Sciences, University of Bologna, Bologna, Italy; 2Institute of Geology, University of Innsbruck, Innsbruck, Austria; 3Institute of Earth Sciences, University of Iceland, Reykjavik, Iceland; 4Swedish Museum of Natural History, Stockholm, Sweden; 5Dipartimento di Scienze della Terra, dell’Ambiente e della Vita, Università di Genova, Genova, Italy; 6Programa de Pós-Graduação em Geodinâmica e Geofísica, Federal University of Rio Grande Do Norte, Natal, Brazil
Hypogene caves are the product of rock dissolution by reactive fluids whose origin is not linked to surface processes or meteoric water circulation. In contrast to "classic" epigene speleogenesis, the migration path of the fluids generally occurs upwards, and the reactivity of the upwelling solutions stems from deep-seated geological processes (e.g., geothermal heat, volcanism, organic matter and hydrocarbon maturation). Interconnected macro-scale hypogene conduits (tens of centimeters up to meter-scale in aperture) have been found down to depths of 4-5 km in many karst reservoirs. The exhumation of hypogene caves, where preserved from collapses and erosion, may advance our understanding of deep-seated porosity-enhancement processes.
Several caves located in the São Francisco Craton (Brazil) have been recently studied due to the presence of SiO2 deposits (chert, quartz, chalcedony) and hypogene morphologies. In particular, the Calixto Cave, 1.4 km long and about 60 m deep, has been investigated using a detailed multidisciplinary approach. The stratigraphic, structural, and geomorphological characterization of the cave has been integrated with petrographic and microthermometric studies on fluid inclusions in quartz filling pore space and fractures. In addition, δ18O and δ30Si analyses were carried out on chert and quartz crystals to assess the origin of SiO2 dissolution-precipitation processes.
Micro-crystalline quartz in the silicified layers replaces the precursor dolomite, forming chert nodules and irregular bands. These cherty layers (which host ~70-80% of the entire cave’s length) show evidence of intense dissolution and represent high-permeability zones. According to silica solubility models, dissolution of quartz is efficient in thermal (> ca. 100-150°C) and alkaline fluids. Evidence of dissolution-recrystallization textures are represented by chalcedony or mosaic (“jigsaw”) quartz, which line the contact of solutional pores and enlarged fractures in the cherts. This chalcedony is followed by the formation of mega-quartz crystals with textures related to: i) boiling (early stage, colloform-plumose quartz); ii) cooling (late stage, massive or zonal quartz); and iii) hydraulic fracturing (quartz-rich breccias).
Our petrographic, microthermometric, and stable isotope (δ18O and δ30Si) data suggest that the quartz deposits found in the silicified layers hosting the main cave passages result from the upwelling of high temperature hydrothermal solutions involving silica dissolution, boiling (early-stage quartz), and cooling (late-stage quartz). The homogenization temperatures of primary fluid-inclusion assemblages (FIAs) in the mega-quartz indicate minimum formation temperatures of 175-210°C.The dissolved salts in primary FIAs were identified as NaCl+CaCl2 by cryogenic Raman spectroscopy and low temperature microthermometric data, resulting in estimated salinity of 18-25 mass.%.
The evidence of dissolution and reprecipitation of silica in Calixto Cave demonstrates the role of hypogene (hydrothermal) speleogenetic processes that drastically modified the petrophysical properties of rocks considered to have very low solubility in most near-surface conditions (e.g., chert, quartzite, silicified carbonate). Circulation of high temperature aqueous fluids may result in the dissolution of quartz-dominated rocks, leading to the formation of high-permeability zones and, potentially, macro-scale karst porosity (partially filled by chalcedony and mega-quartz during boiling/cooling). Our results may help to clarify the origin of dissolution-precipitation processes in many deep carbonate reservoirs where silicification and karst development are closely associated.
New inventoried Karst systems in Central Africa and preliminary paleoclimate proxy analysis applied on the speleothems samples from MRAC collections.
1Royal Museum of Central Africa, Tervuren, Belgium; 2University Marien Ngouabi, Brazzaville, Congo R; 3University of Kinshasa, Kinshasa, RDC
Although knowledge of Karst is of great importance in terms of water resources, risks it can generate for populations and infrastructures, and paleoclimate changes reconstruction, it is currently little studied in central Africa from a geoscientific point of view.
In Kongo-Central, the Karst system is developed in carbonate rocks, which is part of the Neoproterozoic schisto-limestone subgroup. It extends from southwest Gabon to northwest Angola over 1400 km. They cross the DRC and RC from NW to SE over nearly 500km with a width of up to 180 km. The various layers of this system are mainly sub-horizontal. The total thickness of carbonate rocks can reach more than 1000 m.
Currently, multidisciplinary research is underway in this limestone area in the DRC and the Republic of Congo, within the framework of the GeoRes4Dev project (DEA and Ph.D.), funded by the Belgian cooperation.
As part of this work, following the compilation of data from bibliographical sources, information obtained from local scientists, observations on satellite images, and new fieldwork, we now arrive at a compilation of 285 caves, some of which may, however, still be redundant. Only about 145 of them could be located with varying degrees of precision, and of these, 11 were mapped. The longest known cave has nearly 10 km of galleries. Caves generally develop in a subhorizontal way, on 2 or 3 levels.
The current studies are mainly focused on the caves evolution, the hydrogeological network and the structural context affecting the karst system and the speleothems. All of this data will provide a better understanding of the evolution of the karst affecting these areas. In particular, the study of speleothems, which present high quality climatic records, should inform us about paleoclimatic changes. It should be mentioned that the Holocene paleoclimate is so far little studied in DRC and RC and new data will be of immediate interest for understanding climate change in the Intertropical Convergence Zone (ITCZ).
Two main research ideas are in progress:
- U-Th dating has already been applied without success for a sample of stalagmite taken from Mbuji-May (Kasaï, DRC). As our study area is located in the same geological context, we believe that this method is probably also inappropriate due to the low U-Th content in the area. We therefore wish to apply alternative methods to trace the growth chronology of stalagmites in Kongo-Central, DRC and in RC (Radiocarbon, measurement of the isotope O, and trace elements, Mg, Sr, and Ba as well in drop of drop by drop than in calcite stalagmites).
- In Central Africa, there is a considerable lack of knowledge on climate records. It is expected that the studies and the comparison of the paleoclimatic proxies of the speleothems of different localities: Niari in the Republic of Congo¸ Kasaï and Kongo-Central in the DRC in the first step, can help to fill it. Currently, some preliminary analysis are in progress: geochemical proxies (ME and TE) and photometry must be correlated and interpreted with the regional context of Central Africa.
Subaqueous speleothems from Australia’s southern arid-margin
1The University of Melbourne, Australia; 2Australian Nuclear Science and Technology Organisation, Sydney, Australia; 3Institute of Global Environmental Change, Xi’an Jiaotong University, China; 4Flinders University, Australia
Australia’s climate through the Last Glacial Period (LGP) has been primarily reconstructed from pollen sequences taken from bogs and lakes along the coastal fringes of the continent. The vast continental interior is poorly represented by palaeoclimate records since the harsh, arid conditions do not lend themselves to the formation nor preservation of palaeoclimate archives. Sediment sequences from Kati Thanda (Lake Eyre) and dune morphology from upstream fluvial systems indicate at least three distinct periods of lake filling during the LGP. These lake-full periods are indicative of large volumes of water descending from the north, most likely due to an increase in the intensity of the Indo-Australian Monsoon. While indisputable evidence of increased monsoon activity, these records cannot precisely constrain the timing of these pluvial periods, nor can they capture millennial-scale climate variability, or the behaviour of mid-latitudinal climate systems. Speleothems from Mairs Cave, in the Flinders Ranges (South Australia), may present an opportunity to address these issues and provide insight into the past climate of Australia’s southern arid margin.
The study site lies on the boundary between the arid and semi-arid regions and receives rainfall from both the Southern Hemisphere Westerly Winds and the Indo-Australian Monsoon. The cave contains pendulites: stalactites with an external crust of subaqueously precipitated calcite. The stalactites in Mairs Cave were initially submerged ~ 89 ka by the rising of the ground water table, which caused the cave to flood. From that point forward, it appears that the pendulites grew subaqueously during periods groundwater recharge and lay dormant during comparatively dry periods when the water table fell. Preliminary findings suggest that periods of subaqueous growth align with Southern Hemisphere summer insolation maxima, suggesting that the site was receiving enhanced tropical rainfall due to southerly incursions of tropical moisture from the Indo-Australian Summer Monsoon. This is contrary to previous findings that suggest that the IASM was more responsive to Northern Hemisphere winter insolation minima. Growth rate and magnesium concentration in the subaqueous material both appear to be responsive to millennial-scale climate change, both exhibiting increases during Dansgaard-Oeschger events. This too could be explained by an increase in the delivery of tropical moisture from the IASM.
The Last Deglaciation in South America, Past Climate and Environmental Changes as Recorded in Cave Archives
1University of Tübingen, Germany; 2Trinity College Dublin, Ireland; 3University of São Paulo, Brazil; 4Universidade Federal Fluminense, Brazil
Although precipitation amount is considered the main driver of ecological changes in tropical regions, the monsoon evolution as presented by stable isotope paleorecords is inconsistent with vegetation reconstructions in South America. Most pollen records reveal a radical increase of forested areas during the last deglaciation and Holocene period. However, for a large portion of South America δ18O records from speleothems documented a decrease of South American Monsoon intensity. Thus, other factors likely explain these changes, as for example, more effective precipitation and increases of temperature and levels of atmospheric CO2.
Stalagmites have long been used as recorders of paleo-precipitation and monsoon activity over time in tropical and subtropical South America by analyzing δ18O variability. But recent advances show that speleothems also hold potential for reconstructing past vegetation density and soil changes through the combined use of δ13C and 87Sr/86Sr. Caves can also trap sediments eroded above that cave, thereby providing an archive of soil and vegetation evolution from the external environment.
To characterize the paleoclimatic and paleoenvironmental changes during the last deglaciation in South America, we present three studies performed in caves located at different biomes from western, middle and northeastern Brazil. In these caves, were used a multi-proxy approach, including δ13C, δ18O and 87Sr/86Sr ratios in stalagmites, combined with XRF-derived elemental chemistry, δ13Corg, total organic carbon and total inorganic in carbon sedimentary profiles dug in the same caves.
We conclude that the increase of forested areas in the Cerrado biome (Brazilian savanna) from western/central Brazil was drived manly by the global increase of atmospheric CO2. In other hand, the Caatinga biome (dry forest), present northeast Brazil, transitioned from a denser vegetation to the present dry vegetation during mid-Holocene due to reduction of effective precipitation in this area. This characterizes a vegetation dipole over Brazil, which is independent of the previously documented paleo-precipitation dipole over the continent.
UNDERSTANDING THE INFLUENCE OF CLIMATE OSCILLATIONS AND DRAINAGE BASIN REORGANIZATION ON CAVE AND LANDSCAPE EVOLUTION IN THE “VENA DEL GESSO ROMAGNOLA” AREA (ITALY)
1Department of Biological, Geological and Environmental Sciences (BIGEA) – University of Bologna, Bologna, Italy; 2Department of Chemistry, Life Sciences and Environmental Sustainability – University of Parma, Parma, Italy
The importance of caves in the study of past climate and environmental modifications is well established. Their environmental and geological characteristics allow caves to preserve information related to surface dynamics through long time periods, recording them into both chemical (e.g., stalagmites) and physical (e.g., cave sediments) deposits (e.g., Fairchild et al., 2006; White, 2007). In addition, when cave evolution is dependent on surface hydrology, cave morphologies can provide interesting insights on the long-term effects of past climate dynamics on landscape evolution, as caves can preserve information that can be lost at the surface where faster erosional processes occur (e.g., Audra et al., 2007). Bedrock, climate and tectonics are the most important factors influencing the evolution of an epigenic karst system and understanding their specific role in speleogenesis is of great importance for the comprehension of landscape evolution through time.
Columbu et al. (2015) identified climate as the major forcing for the development of the Re Tiberio multilevel karst system (Messinian gypsum of Emilia-Romagna region, Italy). Coupling the cave level altitude (a.s.l.) with speleothem U-Th ages and fluvial terrace remnants, they were able to constrain the formation of the major cave levels during the cold climate phases over the past c.a. 200.000 years.
Within the “EvolGyps” Project (Evolution of Gypsum caves in Emilia-Romagna region) we are extending the approach adopted in Columbu et al. (2015) and Columbu et al. (2017) to the entire area where the Messinian gypsum outcrops. We here present the preliminary results focusing on the comparison of the Re Tiberio karst system and the Abisso Bentini Cave, whose main entrance is about 2 km southeast from Re Tiberio Cave. Both caves are organised in sub-horizontal superimposed levels connected by vertical shafts, and their current resurgences are tributaries of the Senio river. The younger (lower) cave levels appear to have formed in phase in both karst systems, but the older (upper ones) have not, possibly indicating a different organisation of the surface and connected underground drainage basins than today. Indeed, neither bedrock characteristics nor structural lineaments can be accounted for the observed differences so far.
Audra, P., Bini, A., Gabrovšek, F., Häuselmann, P., Hobléa, F., Jeannin, P.-Y., Kunaver, J., Monbaron, M., Šušteršič F., Tognini P., Trimmel H., and Wildberger A. (2007). Cave and karst evolution in the Alps and their relation to palaeoclimate and peleotopography. Acta Carsologica, 36(1).
Columbu, A., De Waele, J., Forti, P., and Montagna, P. (2015). Gypsum caves as indicators of climate-driven river incision and aggradation in a rapidly uplifting region. Geology, 43(6), 539-542.
Columbu, A., Chiarini, V., De Waele, J., Drysdale, R., Woodhead, J., and Forti, P. (2017). Late quaternary speleogenesis and landscape evolution in the northern Apennine evaporite area. Earth Surface Processes and Landforms, 42(10), 1447-1459.
Fairchild, I. J., Smith, C. L., Baker, A., Fuller, L., Spötl, C., Mattey, D., and McDermott, F. (2006). Modification and preservation of environmental signals in speleothems. Earth-Science Reviews, 75(1-4), 105-153.
White W. (2007). Cave sediments and Paleoclimate. Journal of Cave and Karst Studies 69(1), 76-93.