8:30am - 9:00am
A SPELEOTHEM PERSPECTIVE ON CLIMATE-SOCIETY NEXUS IN THE INDIAN-SUBCONTINENT
1California State University Dominguez Hills, United States of America; 2Xi'an Jiatong University, Xi'an, China
Unlike Europe and China, speleothem records of past climate variability from the Indian subcontinent are few and far between. Of the records that currently do exist, many are plagued by coarser temporal resolution and imprecise chronology. Nonetheless, an emerging body of new generation speleothem paleoclimate records is now providing deeper insights into the Indian summer monsoon variability on a wide range of timescales, and perhaps, most profoundly on the timescales of societal interest. In this talk, I will focus on a subset of new speleothem records from the northeastern part of India and will discuss their climatic significance in the context of recent advances in our understanding of the climatic controls of oxygen isotopes in precipitation in the Indian subcontinent. The talk will highlight how these speleothem records in combination with other types of regional proxy records, data assimilation products such as PHYDA (which, blends global proxy records with the dynamics of climate models), and historical documentary accounts from the region, are revealing a rather troublesome history of recurring protracted Indian summer monsoon droughts during the past millennium and beyond. These speleothem-inferred protracted droughts, many corroborated by reliable historical accounts of famines and mass mortalities events, were likely triggered by variable causative mechanisms. Without the benefit of hindsight provided by these new speleothem records, such disastrous events, if were to reoccur again in the future, would be proclaimed as Black Swans—unlikely and unexpected occurrences. However, it is perhaps more appropriate to label these events as Black Elephants—"disasters that are predicted but ignored—a cross between a Black Swan event and the proverbial elephant in the Room” (1) unless a holistic understanding of monsoon variability is incorporated into drought management and mitigation planning that currently discount the possibility of protracted droughts in the region.
1. Lin, Yolanda C., et al. "Asia’s looming Black Elephant events." Communications Earth & Environment 2.1 (2021): 1-4.
9:00am - 9:15am
A c.800-1000CE sub-seasonal scale stalagmite palaeoclimate record from the Yucatán peninsula
1Godwin Laboratory, Department of Earth Sciences, University of Cambridge, Cambridge, United Kingdom; 2Department of Geography and Environmental Sciences, Northumbria University, Newcastle, United Kingdom; 3Department of Earth and Environmental Sciences, University of Minnesota Duluth, Duluth MN, United States; 4Department of Geological Sciences, University of Florida, Gainesville FL, United States
It has now been over 25 years since stable isotope data from lake sediment cores was first used to provide quantitative evidence of drier conditions in the Yucatán peninsula during the Maya Terminal Classic period (c.800-1000CE); a time in which Maya civilisation underwent major depopulations and societal shifts, frequently termed the Classic Maya Collapse. While the number of palaeoclimate proxy records indicating reduced precipitation in the area during the Terminal Classic has now increased, the degree of uncertainty in their chronology and proxy interpretation has precluded analysis of the precise link between decadal and sub-decadal scale drought events and the abandonment of individual Maya archaeological sites on similar timescales. Fedick and Santiago (2022) conclude that an uninterrupted multi-year drought (consecutive years with no significant wet season) would reduce the output of the food crops farmed by the Maya by 89%. As such, assessment of the occurrence of drought events with significant detrimental impact on Maya food supply requires a palaeoclimate record on at least sub-annual timescales.
We present a sub-seasonal-resolution stable isotope record from stalagmite Tecoh06-1, collected from Tzabnah Cave near Tecoh, Yucatán, Mexico, which spans 186 years of the Terminal Classic. By layer counting from both visual images and an X-ray laminograph, then milling at varying resolution to yield 10-20 samples per lamina, we record seasonal-scale annual fluctuations in both δ18O and δ13C. These annual cycles are also present in the calcium-normalised concentration of multiple trace elements, including strontium and barium. With each lamina confirmed to be annual, we have developed a known-duration record which can be temporally fixed by conventional U/Th dating, greatly reducing the associated degree of chronological uncertainty. This is the first local palaeoclimate dataset to record seasonality through the Terminal Classic, and additionally it replicates a lower-resolution record from the same cave, published by Medina-Elizalde et al. (2010), to a satisfactory degree over the sampled period.
Using this combined palaeoseasonal record of stable isotopes and trace element concentrations we can now reliably characterise the 9 multi-year intervals in the recorded Terminal Classic period wherein precipitation remained low year-round. These intervals would have likely been those with the most pronounced detrimental impact on Maya food crop output and contributed most significantly to the societal collapse.
9:15am - 9:30am
Paleoclimatic and paleoenvironmental changes across the south border of the Amazon basin during the late-Holocene
1Institute for Geosciences, Johannes-Gutenberg Universtiät, 55128, Mainz, Germany; 2Department of Geosciences, University of Tübingen, Tübingen, 72076, Germany; 3Institute of Geosciences, University of São Paulo, São Paulo, 05508-080, Brazil; 4Climate Geochemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany
The Amazon Basin holds the world's largest tropical forest and due to its broad extension and equatorial location, the forest is a major center of deep atmospheric convection, playing an important role in global climate regulation and atmospheric dynamics, thus accounting for much of the hydroclimate variability and rainfall balance over South America. Therefore, the thorough investigation of past climate over the basin, both on centennial and millennial timescales, is essential in order to understand its spatiotemporal variability and to provide further understanding on how past climate and environmental changes may have affected pre-Columbian populations, their cultures, migrations and land-use systems. In addition, this long-term historical perspective allows putting projected future social, economic, and environmental impacts of climate change throughout South America in a long-term context.
The paleoclimatic and paleoenvironmental history of the Amazon basin over the last millennia and the behavior of the South American Monsoon System (SAMS) throughout the lowlands have not yet been thoroughly examined due to a lack of records from more central portions of the basin. Here we discuss these past changes based on new high-resolution δ18O and δ13C records from speleothems collected in Cuica cave in the southwestern Amazon Basin, at the core region of the convective activity of the SAMS, and at a vegetation ecotone zone between the Amazon rainforest and the Cerrado biome, the two main biomes of the continent. We demonstrate that the δ18O values from these new records are representative of SAMS variations and that this convective system provides distinct precipitation patterns over the basin. The SAMS was in a neutral phase with homogeneous precipitation between 1000 BCE and 300 CE, whereas drier conditions prevailed over the western side of the basin between 700 and 1200 CE, and an east-west climatic dipole was established over the Amazon Basin after 1450 CE when wetter conditions prevailed over our study site. The speleothem δ13C record indicates changes in local hydrology conditions and changes in vegetation type/density, and it points to an overall tendency toward a more humid tropical forest during the studied period, except for a drier period which correlates with the Medieval Climate Anomaly (MCA). The dynamics of pre-Columbian cultures from southwestern Amazonia seem to have been related to paleoclimatic and environmental changes reported for the region.
Ongoing research now aims to extend the records both temporally and spatially in the region of the Amazon-Cerrado ecotone at the south border of the Amazon basin with new stalagmites from the southeastern border covering the late-Holocene to have a better understanding of the differences and potential connections both in the climatic controls and the shifts in vegetation between southwest/east borders.
9:30am - 9:45am
Central European temperature variations over the past two millennia recorded in a stalagmite from western Switzerland
1Dept. of Environmental Sciences, University of Basel, Switzerland; 2Institute of Global Environmental Change, Xi’an Jiatong University, Xi’an 710054, China; 3Key Laboratory of Karst Dynamics, MLR, Institute of Karst Geology, CAGS, Guilin 541004, China; 4Department of Earth Sciences, University of Minnesota, Minneapolis, MN 55455, USA.; 5Climate and Environmental Physics, Institute of Physics, University of Bern, Switzerland
Most of the Central European temperature reconstructions covering the last two millennia reflect summer rather than mean annual air or cold season temperatures. We present a highly resolved 2000 year-long speleothem-based oxygen isotope (δ18O) record from Milandre Cave in the Swiss Jura Mountains, whose variations are attributed to fluctuations in autumn, winter and spring temperature. Climate in this region is strongly influenced by westerly air masses, making it an ideal site to record climate variability in the North Atlantic and European realm. Calibration using historical temperature data unveils temperature variations of approximately 2°C within the past two millennia, the temperature difference between the warmest decade of the Medieval Climate Anomaly (950–1250 CE) and the coldest decade of the Little Ice Age (1400–1700 CE) amounting to ~1.7°C. In general, higher temperatures were reconstructed in the periods 450–600 CE and 1000–1150 CE, and relatively low temperatures were recorded in the intervals 650–900 CE and 1350–1700 CE. Modeled cold season temperatures for the past millennium compare remarkably well with our reconstruction, and confirm the importance of both, solar forcing and internal variability, in driving Central European climate.
9:45am - 10:00am
Past fires and post-fire impacts reconstructed from a southwest Australian stalagmite
1ANSTO, Lucas Heights, NSW, 2234, Australia; 2School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW, 2052, Australia; 3School of Environmental and Life Sciences, University of Newcastle, NSW, 2308, Australia; 4School of Earth, Energy and Environmental Sciences, Stanford University, CA, 94305, USA; 5School of Earth, Atmospheric and Life Sciences, University of Wollongong, NSW, 2522, Australia; 6School of Earth and Environmental Sciences, The University of Queensland, Brisbane, QLD, 4072, Australia; 7Radiogenic Isotope Facility, School of Earth and Environmental Sciences, The University of Queensland, Brisbane, QLD 4072, Australia; 8Australian Synchrotron ANSTO, Clayton, VIC, 3168, Australia
Stalagmites provide records of past changes in climate, vegetation, and surface events, with cave dripwaters shown to respond to fires. It is, therefore, most likely that these cave mineral deposits capture the environmental effects of palaeo-wildfires in their chemical and physical properties, as well as the climate conditions occurring prior to palaeo-fire events. We analysed multiple proxies in stalagmite (YD-S2) from a shallow cave in south-west Western Australia. These included stable water isotopes via isotope ratio mass spectrometry and trace elements via synchrotron X-ray fluorescence microscopy and laser ablation inductively coupled plasma mass spectrometry. Principal Component Analysis revealed that short term peaks in combinations of phosphorus, copper, aluminium, lead and zinc in the stalagmite correspond to the timing of documented fire events occurring in the modern portion of the record. One particularly significant fire event is identified at 1897 ± 5 CE and shows a clear peak in P interpreted to be derived from ash, and a peak in 𝛿18O interpreted to indicate evaporation of sub-surface water during the heat of the fire. A post-fire increase in organic matter content and a shift in calcite fabric associated with higher and more variable drip rates are consistent with a post-fire changes in surface-cave hydrology resulting from heat-induced deformation of the shallow karst bedrock brought about by the intensity of this fire. The combination of climate and fire sensitive proxies in YD-S2 indicates that the inferred wildfire in 1897 ± 5 CE was preceded by a multi-decadal dry period. We also identify lower and less variable peak phosphorus concentrations in the pre-European period that are consistent with low-intensity cultural burning by Indigenous Australians. The YD-S2 record shows the potential of stalagmites in capturing the climate-fire relationship and the effects of land-management practices on wildfire frequency and intensity.