The hydroclimate change in the hot and arid Arabian Desert under anthropogenic global warming is a subject of ongoing discussions. Climate models project rising mean annual temperatures coupled with decreasing precipitation averaged over Saudi Arabia with regional variance (Almazroui, 2020). Stable isotope analysis on a combined speleothem record from central Arabia revealed recurring local humid periods during globally warmer intervals over the past ~8 million years (Markowska et al., in review). The speleothem record showed a long-term drying trend towards present, which may potentially be controlled by temperature change. The present study aims to reconstruct mean annual air temperatures (MAATs) of central Arabia during humid periods. These temperatures provide valuable benchmark data for past and future climate models in a region where terrestrial climate archives are scarce. Recent advances in speleothem-based paleothermometry facilitate extracting robust MAATs. We present data from several independent paleothermometers: Fluid inclusion isotopes (de Graaf et al., 2020), TEX₈₆ (Meckler et al., 2021; Wassenburg et al., 2021), fluid inclusion microthermometry (Krüger et al., 2011), and dual clumped isotopes (Bajnai et al., 2020). These reconstructions show that recurrent wet intervals during the Miocene to Pleistocene in the Arabian Peninsula occurred at warmer than modern MAATs. We note, however, that temperature is not the only driver of humidity in the Arabian Peninsula and that both dry and humid periods likely existed under a warmer than today’s climate. Therefore, these observations cannot directly be interpreted as indicator that anthropogenic global warming will lead to future wet conditions in Saudi Arabia. Overall, we provide novel quantitative paleoclimate parameters that can inform climate model experiments leading to improved predictions for future climate scenarios.

How to cite: Schroeder, J., Markowska, M., Vonhof, H., Scholz, D., Weber, M., Boivin, N., Groucutt, H. S., Petraglia, M. D., Martinez-Garcia, A., Krüger, Y., Meckler, A. N., Fiebig, J., Nicholson, S. L., and Haug, G.: Warm mean annual air temperatures during Miocene to Pleistocene central Arabian humid periods, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17613, https://doi.org/10.5194/egusphere-egu24-17613, 2024.

While the modern stable isotope lapse rate for precipitation shows a gradient of -0.19 ‰ per 100 meters elevation for Switzerland (Schotterer, 2010), there is only scarce information about the isotope lapse rate in the past and it is usually assumed that they remained constant through time. To investigate the lapse rate in the past, we use speleothems from caves along an altitudinal transect, which contain past drip water preserved in micrometric sized fluid inclusions (0.01 to 0.1 weight %). This drip water corresponds to precipitation water falling above the cave and thus constitutes an excellent archive of past precipitation, allowing us to determine lapse rates in the past. To extract and analyze this water, we used an improved speleothem fluid inclusion water extraction line available at the Quaternary Geology group of the University of Basel. The new design allows us to measure up to ten samples a day.

For this study, we measured more than 100 fluid inclusion samples from various stalagmites in a transect from the Jura mountains to the swiss alps with elevations ranging between 373 and 2’000 meters. These measurements enable us to obtain direct information on past precipitation as well as determine absolute paleotemperatures (Affolter et al., 2019). They allow us to determine the stable isotope and temperature lapse rates for different time intervals, such as Marine isotope stage 5a, the Younger Dryas and the Holocene.

Furthermore, to better understand the water isotopes in cave environments, we have launched (in 2023) the Citizen Science project “Cave Drip Water” in collaboration with various caving clubs in Switzerland and France (https://duw.unibas.ch/de/quartaergeologie/citizen-science/). The purpose of this program is to collect drip water samples and consequently monitor stable isotopes from numerous caves distributed at different elevations across Switzerland and in neighbouring regions. From this data, we will reconstruct a modern cave drip water lapse rate for Switzerland. In addition, it will allow us to investigate the spatial distribution of water isotopes in karst systems and compare it with the most recent water isotope patterns in precipitation from Switzerland. Moreover, these observations will set a baseline for the use of water isotopes analyzed in speleothem fluid inclusion measurements.

Here we present preliminary isotope and temperature lapse rates based on speleothem fluid inclusion water for the Holocene, Younger Dryas and the MIS 5a intervals as well as the first results from the Citizen science project “Cave Drip Water”.

REFERENCES

Schotterer U., Schürch M., Rickli R., Stichler W. (2010). “Wasserisotope in der Schweiz: Neue Ergebnisse und Erfahrungen aus dem nationalen Messnetz ISOT“ Gas, Wasser, Abwasser 2010

Affolter et al. (2019), Sci. Adv. 5 eaav3809, doi.org/10.1126/sciadv.aav3809

How to cite: Kipfer, T., Fleitmann, D., Affolter, S., Hofmeister, E., Häuselmann, A., Lütscher, M., and Cheng, H.: Central European lapse rate based on speleothem fluid inclusions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17753, https://doi.org/10.5194/egusphere-egu24-17753, 2024.

The Eastern Mediterranean including the Black Sea region is influenced by subtropical Mediterranean, temperate European, and continental Asian air masses which make paleoclimate archives from the Black Sea region a valuable source of information about past climatic changes in temperature and rainfall. On glacial interglacial time scales, most information on climate variability in the Black Sea region comes almost entirely from marine/lake sediment cores (e.g. Wegwerth et al., 2015, 2020; Shumilovskikh et al., 2012). In contrast to these paleoclimate archives, oxygen isotope ratios of speleothem calcite (δ¹⁸O) and water isotope ratios (δD_FI and δ¹⁸O_FI) of speleothem fluid inclusions from Sofular Cave in northern Turkey can provide direct information on the isotopic composition of rainfall and, therefore, potentially identify the sources of moisture at the Black Sea coast. During the last 650’000 years most of the δD_FI and δ¹⁸O_FI values plot closer to the Local Meteoric Water Line (LMWL) than to the Eastern Mediterranean Water Line (EMWL). This indicates that the Black Sea was the dominant moisture source for Sofular Cave during glacial and interglacial periods (Fleitmann et al., 2009; Badertscher et al., 2011). In addition, isotope measurements on speleothem fluid inclusions enables us to reconstruct temperature changes. Holocene temperatures of ~15°C to ~20°C are within the range of modern cave air temperatures and proxy records from the Black Sea (Sanchi et al., 2014; Ménot and Bard, 2012). During the last glacial period fluid inclusions indicate a temperature increase associated with Dansgaard-Oeschger warming events.

REFERENCES

Badertscher, S., Fleitmann, D., Cheng, H., Edwards, R.L., Göktürk, O.M., Zumbühl, A., Leuenberger, M., Tüysüz, O. 2011: Pleistocene water intrusions from the mediterranean and caspian seas into the Black Sea, Nature Geoscience, 4 (4), 236–239.

Fleitmann, D., Cheng, H., Badertscher, S., Edwards, R.L., Mudelsee, M., Goktürk, O.M., Fankhauser, A., Pickering, R., Raible, C.C., Matter, A., Kramers, J., Tüysüz, O. 2009: Timing and climatic impact of Greenland interstadials recorded in stalagmites from northern Turkey, Geophysical Research Letters, 36 (19), L19707.

Menot, G., & Bard, E. 2012: A precise search for drastic temperature shifts of the past 40,000 years in southeastern Europe, Paleoceanography, 27(2).

Sanchi, L., Ménot, G., & Bard, E. 2014: Insights into continental temperatures in the northwestern Black Sea area during the Last Glacial period using branched tetraether lipids, Quaternary Science Reviews, 84, 98-108.

Shumilovskikh, L. S., Tarasov, P., Arz, H. W., Fleitmann, D., Marret, F., Nowaczyk, N., Plessen, B., Schlütz, F. & Behling, H. 2012: Vegetation and environmental dynamics in the southern Black Sea region since 18 kyr BP derived from the marine core 22-GC3, Palaeogeography, Palaeoclimatology, Palaeoecology, 337, 177-193.

Wegwerth, A., Ganopolski, A., Ménot, G., Kaiser, J., Dellwig, O., Bard, E., Lamy, F. & Arz, H. W. 2015: Black Sea temperature response to glacial millennial‐scale climate variability, Geophysical Research Letters, 42(19), 8147-8154.

Wegwerth, A., Kaiser, J., Dellwig, O., & Arz, H. W. 2020: Impact of Eurasian ice sheet and North Atlantic climate dynamics on Black Sea temperature variability during the penultimate glacial (MIS 6, 130–184 ka BP), Paleoceanography and Paleoclimatology, 35(8), e2020PA003882.

How to cite: Held, F., Cheng, H., Edwards, R. L., Tüysüz, O., and Fleitmann, D.: Hydrological and temperature variations in the Black Sea region during the last 650’000 years recorded by speleothem fluid inclusions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19221, https://doi.org/10.5194/egusphere-egu24-19221, 2024.

The interpretation of δ¹⁸Oc and δ¹³Cc values of stalagmites within China is still complex, although numerous cave archives have been reported in this region. Present challenges include distinguishing between natural and anthropogenic influences on regional hydrological and environmental changes, in particular due to the increasing human activities during the mid-to late Holocene. Here, we report for the first time the δ¹⁸O_fi and δ²H_fi records of fluids entombed as inclusions during the Holocene (6290 to 690 yr BP) from a stalagmite from southwest China. We excluded measurement-induced artefacts using Rayleigh fractionation models and improved measurement methods, producing reliable results. We observed very high δ¹⁸O_fi and δ²H_fi values during a weak Asian summer monsoon (ASM). Our record reveals six drought events during the mid- and late-Holocene (~950, 1360, 2260, 3450, and 5600 yr BP), which coincide with the weakening of ASM intensity and variations in low latitude forcing, such as tropical sea surface temperature, El Niño/Southern Oscillation, and intertropical convergence zone. In 950-1100 A.D., the dramatic enrichment of δ¹⁸O_fi (magnitude ~7‰) corresponds with the increase in regional population density due to large-scale population migration at this time (historically known as the Jingkang event). The overall coefficient of variation (C.V = standard deviation/mean) of the δ¹⁸O_fi sequence is 125% compared to only 5% for δ¹⁸Oc. Hence, δ¹⁸O_fi seems to exhibit a greater sensitivity to regional environment wet/dry variations than traditional carbonate isotope proxies.

How to cite: Wu, Y., Warken, S., Li, J.-Y., Li, T.-Y., and Frank, N.: Variations in regional hydrological environment and human activities inferred from δ18O and δ2H of stalagmite fluid inclusions in southwest China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10607, https://doi.org/10.5194/egusphere-egu24-10607, 2024.

Hydrogen (δD) and oxygen (δ¹⁸O) stable isotopes contained in speleothem (cave carbonate) fluid inclusion water allow the quantitative reconstruction of past temperatures. Reconstructions can be based either on the use of a regional modern transfer function between isotopes in precipitation and temperatures (expressed in ‰ / °C) or based on the fractionation between the oxygen isotopes measured in the calcium carbonate and in the corresponding inclusion water. One advantage of this proxy is that temperature reconstruction is constrained by chemico-physical processes. Based on a δD gradient of 3.84‰ / 1°C, we reconstructed quantitative temperature variations occurring during the interval 9.0 ka to 7.8 ka BP for the central and western Europe area with a mean temporal resolution of approximately 25 years. The isotope profile shows that the 8.2 ka cold event is characterized by negative shifts in δD and δ¹⁸O consistent with numerous records from across the Northern Hemisphere such as for example Mondsee and Ammersee lake sediments in central Europe or at a larger scale in ice cores from Greenland. Across the 8.2 ka event, the new high-resolution Milandre Cave Fluid Inclusion Temperature (MC-FIT) shows a remarkable similarity with the physically constrained temperature reconstruction from Greenland ice cores that is based on nitrogen and argon isotopes of trapped air (Kobashi et al., 2017). This record, supported by additional speleothems from a neighboring cave, provides a better understanding of the continental temperature evolution across the 8.2 ka event.

Affolter S. et al.: Central Europe temperature constrained by speleothem fluid inclusion water isotopes over the past 14,000 years. Sci. Adv.5, eaav3809. DOI:10.1126/sciadv.aav3809, 2019

Kobashi, T., Menviel, L., Jeltsch-Thömmes, A. et al.: Volcanic influence on centennial to millennial Holocene Greenland temperature change. Sci Rep 7, 1441. https://doi.org/10.1038/s41598-017-01451-7, 2017

How to cite: Affolter, S., Cheng, H., and Fleitmann, D.: Temperature evolution across the 8.2 ka event based on speleothem fluid inclusion water isotopes from Milandre Cave (Switzerland), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18882, https://doi.org/10.5194/egusphere-egu24-18882, 2024.

Speleothems are continental archive used to reconstruct paleoclimate and paleoenvironmental settings at a high resolution of time. One advantage is that they can be precisely dated using Uranium-Thorium dating methods. Speleothems usually contain small amounts of paleowater trapped in micrometer voids named fluid inclusions, which are sealed in the calcite fabric. This water constitutes a witness of past precipitation falling above the cave at the time the inclusion was sealed. To extract and analyze this water, we use a crushing and extraction line available at the Quaternary Geology group of the University of Basel, that allows the simultaneous analyses of fluid inclusion oxygen (δ¹⁸O_fi) and hydrogen (δD_fi) water isotopes. In this study, we analyzed several stalagmites from Milandre Cave (Jura Mountains, Switzerland). Previous studies from this cave have already shown that δ¹⁸O_fi and δD_fi can serve as key-proxies for paleotemperature reconstruction in central Europe (Affolter et al., 2019). For the temperature reconstruction, we use either the oxygen isotope fractionation between calcite and water as a paleothermometer or a transfer function based on the regional modern relationship between the water isotopes in precipitation and temperature. The resulting temperature estimates provide absolute mean annual cave and surface air temperatures, which, however, may be slightly biased towards the cold season. Stalagmites investigated in this study cover several glacial and interglacial periods, allowing us to reconstruct temperatures for the Holocene, Younger Dryas as well as for Marine Isotope Stages 5, 7, 8 and 9. Our preliminary results show absolute mean annual temperature in a plausible range with values ranging between 0°C and 9.6°C. To gain more information about glacial temperature change, we will use stalagmites coming from additional caves located in the western part of the Jura Mountains.

These quantitative paleotemperature snapshots obtained from Milandre Cave, together with those obtained from speleothems from neighboring caves in the Jura Mountains, will allow to document and enhance the comprehension of the temperature evolution of central Europe over the last 300,000 years before present.

Affolter et al. (2019), Sci. Adv. 5 eaav3809, doi.org/10.1126/sciadv.aav3809

How to cite: Hofmeister, E., Fleitmann, D., Cheng, H., Kipfer, T., Häuselmann, A., and Affolter, S.: Central Europe paleotemperature estimates over the last 300,000 years inferred from speleothem fluid inclusion water isotopes from Milandre Cave (Switzerland)  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18609, https://doi.org/10.5194/egusphere-egu24-18609, 2024.

Fluid inclusion microthermometry has emerged as a powerful tool for reconstructing past land temperatures from speleothems. An implicit assumption of the method is that the closing age of the fluid inclusions is equal to the age of the surrounding calcite, and thus, that the reconstructed temperatures are representative of the cave temperature at which the calcite layers formed. The present study, however, demonstrates that this assumption does not hold true for all stalagmites.

Here we show as an example our results obtained from stalagmite SSC01 from Snail Shell Cave (Northern Borneo), that spans the last ~27,000 years, and that was previously investigated for hydroclimate reconstructions (Partin et al., 2007). A temperature record was reconstructed by means of nucleation-assisted microthermometry (Krüger et al., 2011) by analysing ~20 – 70 individual fluid inclusions in each of the 34 growth bands along the growth axis of SSC01. The Holocene part of the record yields near Gaussian-shaped distributions within coeval fluid inclusion assemblages, while the glacial and early deglacial part shows a considerable spread among seemingly co-eval inclusions, with bimodal distributions. When applying a Gaussian deconvolution routine, we find that the warmer part of these distributions consistently yields temperatures resembling late deglacial or Holocene temperatures. Temperatures of the colder mode of the distributions, in contrast, reflect glacial and deglacial conditions showing a clear deglacial warming trend that closely follows atmospheric CO₂ and Southern Hemisphere warming.

We hypothesize that the warmer mode of these bimodal distributions is a result of open porosity, networks of interconnected cavities that sealed off from the environment towards the end of the glacial Termination, i.e., at a temperature that was significantly higher than the formation temperature of the surrounding calcite host. This interpretation is further supported by petrographic observations, revealing that the glacial and deglacial part of the stalagmite is characterized by frequent alterations of columnar open fabrics (Frisia et al., 2015) and organic-rich micritic layers with high porosity. We suppose that open porosity in stalagmites can occur both vertically along the columnar crystal boundaries and also laterally along specific growth layers.

Bimodal temperature distributions in seemingly coeval fluid inclusions can arise due to temporary open porosity, provided that the temperature difference between the different closing ages of the inclusions is large enough. Our findings emphasize the need for careful consideration of fabric-related factors that can affect the temperatures derived from fluid inclusions.

References:

Frisia, S (2015). Microstratigraphic logging of calcite fabrics in speleothems as tool for palaeoclimate studies. Int. J. Speleol. 44, 1–16.

Krüger, Y. et al. (2011). Liquid–vapour homogenisation of fluid inclusions in stalagmites: Evaluation of a new thermometer for palaeoclimate research. Chem. Geol. 289, 39–47.

Partin, J.W., et al (2007). Millennial-scale trends in west Pacific warm pool hydrology since the Last Glacial Maximum. Nature 449, 452.

How to cite: Løland, M. H., Krüger, Y., Pasqualetto, L., Frisia, S., Borsato, A., Partin, J. W., Adkins, J. F., Cobb, K. M., and Meckler, A. N.: Fluid Inclusion Microthermometry in Borneo stalagmites: Investigating the role of fabric and open porosity on temperature reconstructions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18793, https://doi.org/10.5194/egusphere-egu24-18793, 2024.

Clumped isotope measurements of carbonates and stable isotope analyses of water trapped in fluid inclusions are both promising techniques to determine carbonate formation temperatures. Cave-hosted carbonate deposits (speleothems) would be excellent targets for such studies, but kinetic fractionations and diagenetic influences frequently deteriorate the temperature data obtained with these methods. However, subaqueous carbonate deposits may provide reliable data as kinetic fractionations are less significant in underwater environment. In the present study subaqueous carbonate formations were investigated, whose formation temperatures were directly measured in the water. Additionally, temperatures calculated from oxygen isotope fractionations between calcite and fluid inclusion hosted water were compared with clumped isotope temperatures obtained for subaqueous carbonate formations in cave-hosted lakes. The clumped isotope temperatures fit the measured and calculated temperatures within the analytical precisions. Our study shows that subaqueous carbonate speleothems are useful targets for clumped isotope and inclusion water analyses, and therefore they are valuable paleotemperature archives.

How to cite: Demény, A., Berentés, Á., Rinyu, L., Kovács, I., Surányi, G., and Virág, M.: Subaqueous carbonate speleothems as paleotemperature archives –clumped isotope thermometry and stable isotope compositions of inclusion-hosted water, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17363, https://doi.org/10.5194/egusphere-egu24-17363, 2024.

Clumped-isotope (Δ₄₇) measurements from speleothem calcite have the potential to record formation temperatures with an uncertainty of ± 2°C but are strongly impacted by kinetic effects during mineral precipitation that lead to isotopic disequilibrium and erroneously high-temperature estimates. The application of dual clumped-isotope (Δ₄₇-Δ₄₈) measurements can identify the influence of kinetic effects and has the potential to provide temperature estimates that are corrected for the degree of isotopic disequilibrium, though this involves a decrease in precision (± 4.5°C). The concentration of noble gases in water that is trapped in fluid inclusions in speleothems is another independent estimate of paleo-temperatures that is based on the temperature dependence of noble gas solubility in freshwater systems.

We combine these two newly emerging techniques by applying dual-clumped isotope (n = 15) and fluid inclusion noble gas measurements (n = 3) to a speleothem from McLeans Cave, located in the western foothills of the Sierra Nevada, that grew during the last deglaciation (~11 to 19 ka). We obtain temperature estimates using the noble gas measurements as well as using the Δ₄₇ measurements for samples that do not exhibit isotopic disequilibrium in dual clumped-isotope space and compare these estimates with other western US temperature records from proxy records and climate model simulations. Many of the dual clumped-isotope samples, however do exhibit isotopic disequilibrium. We assess the degree to which disequilibrium can be corrected for using dual clumped-isotopes and test the sensitivity of these isotopic relationships to different published corrections to assess the implications for estimates of paleo-temperatures. Additionally, we compare the new dual-clumped isotope data with coeval d¹⁸O and d¹³C measurements, as well we previously collected measurements of d¹⁸O and d²H from fluid inclusions in the sample to investigate what processes may be driving the isotopic variability in both speleothem calcite and fluid inclusion water in this sample.

How to cite: de Wet, C., Wortham, B., Stolper, D., Mukhopadhyay, S., and Montañez, I.: Deglacial temperature estimates from dual clumped-isotope measurements and fluid inclusion noble gas concentrations in a stalagmite from McLean’s Cave, western Sierra Nevada, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13102, https://doi.org/10.5194/egusphere-egu24-13102, 2024.

Low latitudes play a key role in the Earth's climate system, receiving the highest amount of solar energy that is redistributed across the globe through atmospheric and oceanic circulation. The last glacial cycle has been characterized by millennial-scale climate oscillations, marked by large and rapid temperature swings in the North Atlantic region accompanied with opposite and smaller temperature variations in the Southern Hemisphere. In the context of these millennial scale climate fluctuations, we seek to understand the tropical climate behaviour, determining whether it followed the Northern Hemisphere pattern or the Southern Hemisphere pattern and atmospheric CO₂.

In this study, nucleation-assisted microthermometry (Krüger et al., 2011) was used to determine stalagmite formation temperatures based on fluid inclusion liquid-vapor homogenization. The method was applied to SC03, a stalagmite from Secret Cave (Gunung Mulu National Park, Northern Borneo), previously studied for changes in precipitation (Carolin et al., 2013). Here we reconstructed a quantitative land temperature record, covering selected Dansgaard-Oeschger cycles during MIS 3 (42-50 ka) as well as during MIS 5a and MIS 4 (60-81 ka). Our preliminary findings suggest that tropical temperature did not follow Northern Hemispheric patterns but there appears to be a relationship with atmospheric CO₂ levels. This aligns with previous findings from the last glacial termination derived from another stalagmite from the same cave (Løland et al., 2022). Additionally, we investigated whether there is any evidence of a significant land temperature change in the period immediately following the Toba super eruption (Sumatra, Indonesia),  ca. 73.8 ka. Our study contributes to a broader understanding of the interplay between low and high latitude climate during millennial-scale reorganizations of the global climate system.

How to cite: Afonso, C., Løland, M., Carolin, S., Krüger, Y., and Meckler, N.: Where do tropical land temperatures sit on the bipolar see-saw? , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13062, https://doi.org/10.5194/egusphere-egu24-13062, 2024.

Age-depth models are widely used to build chronologies from proxy records and are most often implemented for speleothems due to age uncertainties and lower resolutions. In this study, we use a variation of the accumulation rate method to perform a pseudo-proxy reconstruction of large-scale variability in monsoon precipitation using synthetic oxygen isotope records from speleothem sites and the isotope-enabled ECHAM/MPI-OM climate model. We present a probabilistic approach to synchronize speleothems by informative priors of oxygen isotope data and individual independent age constraints. This is achieved by co-estimating the regional δ¹⁸O variations through time, where δ¹⁸O variability is modeled using Gaussian processes and a Bayesian model is further used for the individual speleothem chronologies. The method is tested using synthetic speleothem data generated from the last millennium-long climate model simulation and corrupted through realistic noise from speleothems in the Indian Ocean region from the SISALv2 database. Through the creation of a millennium-long reconstruction, we aim to study the atmospheric dynamics from the reconstruction over the Asian region to help us further constrain the drivers, responses to, and changes in the variability of the monsoon. By synchronizing the time series of oxygen-isotope data through the incorporation of accurate and realistic depth-dependent age uncertainties, this modeling approach may lead to advancements in handling speleothem data and climate model simulations for regional to global evaluations of variability and past climate reconstructions.

How to cite: Axelsson, J., Nilsson, A., Suttie, N., and Sjolte, J.: A Bayesian framework to model speleothem oxygen isotope data with age uncertainties, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8504, https://doi.org/10.5194/egusphere-egu24-8504, 2024.

To better estimate effects of current climate change on the water cycle in the highly variable tropical region, past periods of similarly warm climate conditions can provide unique insights. The interglacial phases of the past 800,000 years are promising targets for this purpose, since these provide a natural variety of different climate configurations. While several reconstructions of past interglacial periods are available, the terrestrial, and in particular tropical regions are still under-represented in the record. Speleothems can be used to observe changes and effects on the eco- and climate system as well as their coupling on seasonal to millennial time scales, which usually cannot be resolved by climate model simulations.

This project aims to further close the research gap of these regions with investigations of stalagmites from Cueva Larga, Puerto Rico. Cueva Larga is a well-monitored location^1,2,, and speleothem records from this cave have demonstrated a high sensitivity to regional and global climatic variations, in particular changes in the position of the ITCZ, Atlantic sea surface temperatures and ocean circulation^3,4. First precise ²³⁰Th/U ages on previously collected stalagmites show the potential to reconstruct climatic variations during parts of the past interglacials of the past 300,000 years, i.e., MIS1, MIS, 5, MIS7, and MIS9. In the next step, time series from high-resolution trace element and stable isotope measurements (δ¹⁸O and δ¹³C) from these interglacials will be conducted.

The multi-proxy speleothem time series will allow to improve the quantitative and qualitative understanding of precipitation intensity and variability during interglacials and also help to constrain both the sensitivity of the Earth system in the tropics to different climatic drivers and the extent of current climate change compared to natural variability.

References:

1 Vieten et al. (2017). Monitoring of Cueva Larga, Puerto Rico—A First Step to Decode Speleothem Climate Records. Advances in Karst Science, Springer International Publishing, p.319-331

2 Vieten et al. (2018). Hurricane Impact on Seepage Water in Larga Cave, Puerto Rico. Journal of Geophysical Research: Biogeosciences, Vol. 123, No. 3

3 Warken et al. (2020). Persistent Link Between Caribbean Precipitation and Atlantic Ocean Circulation During the Last Glacial Revealed by a Speleothem Record from Puerto Rico. Paleoceanography and Paleoclimatology, Vol. 35, No. 11

4 Warken et al. (2022). Last glacial millennial-scale hydro-climate and temperature changes in Puerto Rico constrained by speleothem fluid inclusion δ¹⁸O and δ²H values. Climate of the Past, Vol. 18, No. 1

How to cite: Mielke, A., Warken, S., Garcia, N., Charles, C., Keppler, F., Rivera Collazo, I., Acosta Colon, A., and Winter, A.: Towards a comparison of interglacial climate variability in the tropics during the last 300.000 years, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20041, https://doi.org/10.5194/egusphere-egu24-20041, 2024.

While the Atlantic Meridional Overturning Circulation (AMOC) is understood to be weakening as a consequence of anthropogenic climate change, the precise onset of this decline remains subject of debate. There are two principal hypotheses surrounding the initiation of the slowdown: (a) it began in the mid-twentieth century in response to escalating atmospheric carbon dioxide concentrations, and (b) the trend started in the mid-nineteenth century, resulting from the increased freshwater fluxes associated with the end of the Little Ice Age (LIA). Here, we present a monthly resolved record of magnesium concentration extending back to 1456 derived from a Bermudan stalagmite. We use this proxy record to reconstruct sea surface temperature (SST) by calibrating the data to a previously published SST record, and with it derive an AMOC fingerprint spanning more than 550 years. From this we aim to decipher an estimate for the initiation of the observed AMOC decline within the context of its subsequent manifestations. 

How to cite: Forman, E., Baldini, J., Jamieson, R., Lechleitner, F., Baldini, L., Breitenbach, S., and Macpherson, C.: Examining the weakening of the AMOC using a Bermudan Stalagmite , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11252, https://doi.org/10.5194/egusphere-egu24-11252, 2024.

The Little Ice Age (LIA) was a predominant anomalously cold event on Earth that occurred from c. 1350 to c. 1850 with a near-global signature.  Many records from different paleo archives located throughout the greater Caribbean show hydroclimate heterogeneity throughout all or part of this period. Here we present new evidence from the Guatemalan stalagmite GU-Xi-1 that contains a prolonged period of persistently heavy oxygen isotope values indicating a long-term major dry event (MDE) which started rather abruptly around 1400 CE and lasted for about approximately 200 years (age uncertainty c.50 years), with both onset and termination likely occurring within a couple of decades. The age model and hence, the timing of the Xibalba MDE is regarded as robust because they are consistent with a change in calcite precipitation that produced the “L” layer in the Xibalba speleothem.  This layer which is associated with drying in speleothems could be precisely dated and bracketed using U/Th.  In this contribution, we present the Gu-Xi-1 record and discuss possible mechanisms underlying the reconstructed Mesoamerican megadrought and their connection with natural climate forcing agents active in the period.

How to cite: Winter, A., Zanchettin, D., Warken, S., Lachniet, M., Rubino, A., Burnett, A., Cheng, H., Jury, M., and Miller, T.: The sudden and prolonged Mesoamerican megadrought (1400-1600 CE) during the early LIA, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12336, https://doi.org/10.5194/egusphere-egu24-12336, 2024.

The hydroclimatic variability of southern Africa during the Quaternary is comparatively poorly know, partly due to the scarcity of suitable terrestrial paleoclimate archives in this semi-arid to arid region. Speleothems offer great potential for filling these knowledge gaps, and carbonate units exhibiting karst features are present in several regions. One such area is the Otavi Mountains of northeastern Namibia, where caves have developed in Neoproterozoic carbonate rocks. However, despite encouraging early work, only two speleothems from one Otavi cave have so far been studied using state-of-the-at techniques.

As part of a research programme investigating the origin of caves in the Otavi Mountains, we were given permission to also sample speleothems, focusing on flowstones, which are locally abundant. Although most of these formations are currently inactive, there are local exceptions that allow to obtain proxy records covering also the Holocene. Most of the flowstones, however, were active during the late Pleistocene, with a marked growth pulse during the deglacial. Remarkably, none of the 70 dated subsamples formed during the Last Interglacial. The picture that emerges from this preliminary dataset suggests favoured speleothem growth (and higher average growth rates) during periods when the Intertropical Convergence Zone was shifted far to the south as a result of cold boreal conditions.

While other parts of Namibia, such as the Namib Desert, may be more sensitive to hydroclimate changes leading to complete growth stops during interglacials, the higher rainfall and cooler temperatures in the Otavi Mountains open the door to obtain longer proxy records characterized by fewer hiatuses.

How to cite: Leitgeb, L., Koltai, G., Dublyansky, Y., Zhang, H., Cheng, H., and Spötl, C.: Speleothems in northeastern Namibia as archives of hydroclimatic changes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21841, https://doi.org/10.5194/egusphere-egu24-21841, 2024.

The South American Monsoon System (SAMS) plays an important role in the hydroclimate variability and rainfall patterns across South America. Stemming from its convective core in the southwestern Amazon basin, the South Atlantic Convergence Zone (SACZ) is a southeastward convection band, being a critical component of SAMS responsible for large-scale moisture transport, particularly over Central Brazil. Previous paleoclimate studies suggest that SACZ has changed over time, usually associated with changes in the SAMS, and there are current debates regarding the nature of SACZ, shifts in position, size, and intensity, and their potential impacts on vegetation changes. Therefore, this study addresses these debates for the last 16,000 years based on a novel multi-proxy paleorecord of δ¹⁸O, δ¹³C, and Sr isotope ratios (⁸⁷Sr/⁸⁶Sr) from a stalagmite collected in São Mateus Cave at the northeast limits of SACZ in central Brazil. This site is therefore under the regime of SACZ, with a climate characterized as tropical semi-humid with a rainy summer season and a dry winter.

The inclusion of Sr isotope data enhances our interpretation of past local climate variability since changes in ⁸⁷Sr/⁸⁶Sr can provide valuable information about the water residence in the epikarst and changes in soil composition. Furthermore, as São Mateus Cave lies within the Cerrado biome, it offers a unique insight into the past climate and environmental changes in central Brazil due to its distinct floral compositions influenced by factors such as location, soil, rainfall distribution, and fire frequency. Comparisons with other paleoclimate data from SACZ-influenced sites are made to access climate and vegetation changes in different locations within this convective band, particularly over larger time scales, such as the transition from the Late-Pleistocene to the Holocene and longer trends. We demonstrate that even though there is a common change in the regional δ¹⁸O signal connected with SACZ variations, differences in vegetation and local moisture between northern and southern SACZ limits are evident albeit being in the same biome. This multi-proxy approach, combining traditional stalagmite proxies with high-resolution LA-MC-ICP-MS Sr isotope analysis, offers a better understanding of SACZ changes and their implications for Central Brazil's climate and environment. 

How to cite: Della Libera, M. E., Scholz, D., Vonhof, H., Stumpf, C., Weber, M., Cauhy, J., Cruz, F. W., Stríkis, N., and Novello, V. F.: South Atlantic Convergence Zone impacts on climate and vegetation changes over the last 16,000 years in Central Brazil based on a speleothem multi-proxy record, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10458, https://doi.org/10.5194/egusphere-egu24-10458, 2024.

Heinrich events (HEs), characterized by massive and rapid ice-rafted debris from Laurentide Ice Sheet into the Labrador Sea as far south as the Iberian Margin, are observed in some stadial periods during the last glacial, however, it is still unclear regarding to the trigger and response mechanism of the HEs. A landmark work by Wang et al. (2004) was one of the first studies to associate tropical rainfall in southern Hemisphere with HEs, showing wet periods in tropical northeastern Brazil, a region that is currently semi-arid but very sensitive to the hydroclimate changes related to the cold events occurred in the northern Hemisphere, are synchronous with HEs in the North Atlantic. After two decades, we have a new chance to study the relationship between hydroclimate in NE Brazil and cold events in the North Atlantic in the light of much more new speleothem records obtained from TBV and TBR caves, NE Brazil. Here we show evidence of stalagmite growth periods and δ¹⁸O records during the last 90 kyrs from NE Brazil, in addition to the HEs observed by Wang et al. (2004), we have newly found wet periods during the HE2 and HE3 and GS 5-8 that were not discovered before. It indicates that previous conclusions that the orbital insolation also modulated these events on millennial timescales need to be reinterpreted, and also provides new insights to understand the mechanisms of the HEs and why the HEs only occurred in some Heinrich Stadials. Additionally, we also compare detailed structures of each HE inferred from cave δ¹⁸O records in NE Brazil with sea surface temperature and other records in the Atlantic realm, which deepens our understanding of the trigger-response mechanisms of the HEs and its effect on the hydroclimate in the NE Brazil.

How to cite: Zhang, H., Cheng, H., Cruz, F. W., Auler, A. S., Spötl, C., Wang, X., Stríkis, N. M., Zong, B., and Edwards, R. L.: New insights of the Heinrich events inferred by speleothems from Northeast Brazil, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7289, https://doi.org/10.5194/egusphere-egu24-7289, 2024.

The paleoclimate and paleoenvironmental conditions of Crimea are scarcely known due to the lack of high-resolution archives in this area. Crimean speleothems have a high potential of providing valuable information and filling the knowledge gap on the paleoclimate in the northern part of the Black Sea area.

We acquired six well-dated stalagmite records from Crimean caves which grew during different intervals of the Holocene and MIS 3 with a good overlap, spanning from 2.7 (± 0.1) to 58.0 (± 0.0) ka BP. Records of δ¹⁸O and δ¹³C show some resemblance to the Sofular record from the southern Black Sea coast. However, based on our knowledge of the modern pathways of moisture supply to Crimea (with only ca. 14 % of moisture originating from the Black Sea surface^[1]), it can be expected that the controls of stalagmite δ¹⁸O values may be different in the south and north of the Black Sea. δ¹³C records show larger shifts than the δ¹⁸O records on the millennial time scale (e.g., Heinrich events) especially during MIS 3. None of the speleothems grew during MIS 2, probably reflecting arid and cold climate conditions.

These records are being analyzed and compared with other paleoclimate records to better understand: (1) the local hydrological dynamics and climate history during the Holocene and MIS 3, (2) the differences in climate conditions between the southern and northern Black Sea regions, and (3) the spatio-temporal teleconnection between the North Atlantic realm and the study area.

^[1] Langhammer et al. (2021) doi: 10.1029/2021EA001727

How to cite: Li, Y., Dublyansky, Y., Spötl, C., Cheng, H., Tokarev, S., and Amelichev, G.: Paleoclimate reconstruction based on speleothems from the Crimean Peninsula, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6289, https://doi.org/10.5194/egusphere-egu24-6289, 2024.

The study of glacial to interglacial climate transitions is extremely important for understanding the full scale of climate variability from global to local scale. Unfortunately, there are large areas where multimillennial paleoclimate timeseries are unavailable. Southern Caucasus, is such a region as currently only a few continental climate time series extend beyond the short instrumental records. Importantly, temperature-related proxies are virtually absent here, thus impeding to evaluate how global-scale rapid climate instabilities propagate and impact this area. This work provides the first paleoclimate reconstruction from Georgia (Southern Caucasus) spanning approximately the last 13500 years. Four stalagmites named Zak-1, Zak-3, Zak-4 and Zak-6, measuring 46, 50, 55 and 102 cm respectively, were collected from the Zakariasklde Cave (42°10′ N; 43°20′ E). Dated by the U-Th method, Zak-1 was deposited between 3.1^+0.04/_-0.03 to 0.32^+0.46/_-0.44 ka (ka = kiloyears before 1950 AD); Zak-3 between 13.48^+0.07/_-0.08 to 10.11^+0.05/_-0.09 ka; Zak-4 between 12.01^+0.08/_-0.09 to 9.73^+0.53/_-0.61 ka; and Zak-6 between 8.77^+0.07/_-0.08 to 0.71^+0.16/_-0.13 ka, with a possible hiatus between 4.45^+0.19/_-1.49 and 3.27^+1.35/_{- 0.34} ka. Timeseries of δ¹⁸O-δ¹³C from calcite show the main patterns of temperature variations during the last glacial-interglacial shift as well as throughout the Holocene, which mostly agree in pace and tempo with global records (i.e., Greenland ice and Atlantic/Mediterranean sediment cores). Then, δ¹⁸O-δ²H from speleothem fluid inclusions (FI) are preliminarily applied to quantitatively calculate temperatures. Conveniently, FI resulted well aligned with the modern meteoric water line in Georgia, thus indicating that isotopic fractionation occurred during the karst flow-path and calcite precipitation was negligible. FI-derived temperatures document the effects of climate warming in Southern Caucasus related to the last deglaciation, with a ca. 4.5ºC increase of average temperatures from ~12 to ~10 ka. Paleotemperatures during the Holocene instead presents a gradual decrease of around 2ºC from ~10 ka to ~3 ka. This potentially supports the existence of a Holocene thermal maximum during the Early Holocene, which is still a matter of debate. However, calculation uncertainties make this finding debatable. The interpretation of the record is refined by considering changes of rainfall (e.g., amount, provenance/source and seasonality) as well as soils (e.g., vegetation bioactivity). To comprehend the climate mechanisms of South Caucasus climate during rapid global instabilities, the Zak-timeseries is compared to the others from different climate regimes to advance the current characterization of regional climate shifts. Therefore, the results of this study certainly help to further investigate possible climatic teleconnections on a regional to global scale.

How to cite: Asanidze, L., Columbu, A., Fleitmann, D., Burns, S., Lezhava, Z., Tsikarishvili, K., Zanchetta, G., Natali, S., and McGee, D.: The first multi-proxy speleothem paleoclimate record from Georgia and calculations of temperature variations during the last ~ 13500 years , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14861, https://doi.org/10.5194/egusphere-egu24-14861, 2024.

            Conventional models of speleothem growth require percolation through a biologically active soil layer, uptake of soil-respired CO₂, and resulting carbonic-acid dissolution of the host rock. Within this model, speleothem growth is inhibited when the mean temperature of the soil-karst-cave system falls below the freezing point of water. Hence, speleothem growth hiatuses have been interpreted at high-latitude sites to indicate permafrost conditions or glacial cover. Paradoxically, however, speleothem growth during presumably ice-covered intervals has been documented in studies of Alpine and North American caves. To explain how growth could proceed despite subzero mean annual air temperature and the absence of soil, previous work has proposed a mechanism that invokes: 1) the oxidation of sedimentary sulfides to promote sulfuric-acid dissolution of host rock; and 2) buffering of ground temperatures by a warm-based glacier above the cave site that maintains the epikarst and cave within the 0°C isotherm. In this scenario, infiltrating meteoric water is derived indirectly from basal glacial melt and seasonal moulin drainage, which act as a low-pass filter with respect to transference of the oxygen-isotope composition and associated climate signal.

            Although individual components of the proposed mechanism have been observed in modern analog settings, there has been no comprehensive attempt to elucidate or constrain these processes through geochemical proxy data. Here we present preliminary data from speleothems in the Western Alps (Austria, Switzerland, France) and Western Caucasus (Abkhazia) that grew subglacially or in close proximity to the ice margin, according to U-Th dating and glacier reconstructions. Based on these results, we attempt to define multiproxy diagnostic criteria to identify intervals of subglacial conditions. First, we investigate how a switch to predominantly sulfuric-acid dissolution impacts the carbon-isotope and trace-element composition of calcite. We find that enhanced host rock contributions to the dissolved inorganic carbon pool substantially raise δ¹³C and dead-carbon fraction, as well as increase the variance in prior calcite precipitation, as interpreted from trace-element data. We evaluate these data through proxy system modeling of a subglacial setting; however, information from these proxies is limited as they are impacted by a multitude of processes. Therefore, we test whether speleothem S/Ca and δ³⁴S are more direct proxies for sulfide oxidation. Finally, we consider paleothermometric methods to test whether cave temperatures are near zero, as the proposed mechanism requires. If successful, the identification of subglacial speleothem archives may substantially improve glacial reconstructions by providing vital constraints on ice-sheet properties for paleomodeling, in addition to yielding proxy reconstructions of surface climate during glacial intervals, when most terrestrial archives are inactive.

How to cite: Baker, J., Honiat, A., Skiba, V., and Spötl, C.: Multiproxy diagnostic criteria to identify subglacial speleothem growth: test cases from the European Alps and Western Caucasus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14529, https://doi.org/10.5194/egusphere-egu24-14529, 2024.

The Asian summer monsoon (ASM) represents a significant and expansive element within the global climate system. While speleothem δ¹⁸O records offer robust characterization of millennial-scale ASM variations over the last 640 ka (thousand years), limited data exists regarding the ASM's behavior preceding the U-Th dating limit of approximately 640 ka. This includes periods such as the mid-Pleistocene Transition (MPT, ~800-1200 ka) and the pre-MPT era. In this study, we present two meticulously calibrated high-resolution speleothem δ¹⁸O records sourced from central China. These records span three distinct periods: 640–615, 690–660, and 1,360–1,310 ka BP ( thousand years before present, the present defined as 1950 CE). The absolute dating of these records is accomplished via laser ablation and isotope dilution U-Pb methods. Our meticulous tuning aligns these records with the summer insolation (690–660 and 1,360–1,310 ka BP) and the preceding record (640–615 ka BP). Our findings indicate a close association between millennial-scale weak ASM occurrences and North Atlantic stadials and Antarctic warming events within the period of 685–675 ka BP, similar to previously established connections within the last 640 ka. Furthermore, millennial-scale ASM variations occurred prior to the MPT, specifically during the period of 1360–1310 ka BP, albeit with relatively smaller amplitudes in comparison to those observed after the MPT in the last ~690 ka. We hypothesize that reduced freshwater forcing in the North Atlantic and/or altered freshwater routing to the Gulf of Mexico through the Mississippi drainage system might have resulted in a less pronounced weakening of the Atlantic Meridional Overturning Circulation (AMOC) before the MPT, thereby leading to smaller amplitudes in millennial-scale ASM variations observed during 1360–1310 ka BP.

How to cite: Niu, X., Wang, J., Kang, L., Zhang, H., Cheng, H., and Li, Y.: Increased millennial-scale monsoonal circulation amplitude across the mid-Pleistocene transition revealed via speleothem records, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5107, https://doi.org/10.5194/egusphere-egu24-5107, 2024.

How to cite: Cauhy, J., Scholz, D., Vonhof, H., Stríkis, N., Della Libera, M. E., Novello, V. F., and Cruz, F. W.: Stalagmite-based cave flood records as a proxy for reconstruction of extreme rainfall frequency over the Holocene from two different cave sites in South-eastern Brazil, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11131, https://doi.org/10.5194/egusphere-egu24-11131, 2024.

Speleothems are not only valuable archives for reconstructing paleoclimate but can also witness climatic events including storms and floods. Two speleothems have been collected from nearshore caves on the islands of Jura and Islay, on the west coast of Scotland. The Jura cave is ~62 km northeast of the one on Islay, yet intriguingly U/Th dating shows that both speleothems began to grow at ~2,400 yr BP. This simultaneous start in calcite deposition could be related to relative sea-level change. Both speleothems have a fine-scale colour banding, and these layers are of a similar age. The dark brown layers in the Islay speleothem correlate well with storm events identified from the island’s peat bogs (Kylander et al., 2020). The black layers in the Jura speleothem formed due to the presence of manganese oxides and are thought to be indicative of cave flooding (Belli et al., 2017). We therefore suggest that periodic changes to the chemical composition and oxygenation of dripwaters in the Jura and Islay caves reflect near-synchronous Late Holocene storm events and associated flooding on the west coast of Scotland.

Belli, R., et al. (2017). Investigating the hydrological significance of stalagmite geochemistry (Mg, Sr) using Sr isotope and particulate element records across the Late Glacial-to-Holocene transition. Geochimica et Cosmochimica Acta, 199, 247–263.

Kylander, M. E., et al. (2020). It’s in your glass: A history of sea level and storminess from the Laphroaig bog, Islay (southwestern Scotland). Boreas, 49(1), 152–167.

How to cite: Xie, K., Lee, M., Persano, C., Faithfull, J., Cheng, H., and Lawson, T.: A history of storminess and flooding on the west coast of Scotland reconstructed from metamorphic cave-grown speleothems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7735, https://doi.org/10.5194/egusphere-egu24-7735, 2024.

Geochemical anomalies within speleothems serve as crucial indicators of environmental changes. While research predominantly focuses on calcite-dominated formations, understanding the significance of aragonite is essential for a comprehensive grasp of past climate dynamics. This study presents high-resolution records, based on ²³⁰Th/U dating, stable isotopes (δ¹³C) and trace elements analysis in recent aragonite growth lamina near the calcite top in three speleothems from Mawmluh Cave, Meghalaya, India. Covering a total of 163 years (2022 to 1859 CE), the research explores the environmental impact on the cave system, especially in relation to nearby industrial activities. Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) was utilized to analyze trace elements (e.g., Mg, Sr, Ba, U, P, Y, Pb, Al, Th, etc.) in the recent aragonite growth lamina. Detected trace elements (Pb, Zn, Mn, etc.) at trace concentrations, alongside current δ¹³C values, may be linked to emissions from a nearby cement plant and open-cast mining activities, acting as potential indicators of anthropogenic influence. All three speleothems displayed transitions from calcite to aragonite near the top, suggesting a significant alteration in the cave system over time, potentially induced by human activities. Anthropogenic factors may contribute to this transition, with specific elements acting as key markers. Future studies on the geochemical signatures of aragonite formations promise to fill existing gaps, offering a nuanced perspective on paleoclimatic and paleoenvironmental conditions.

Keywords: speleothems, aragonite formations, trace elements, stable isotopes, anthropogenic impact, Mawmluh Cave.

How to cite: Dildi, D., Weber, M., Vonhof, H. B., and Scholz, D.: Unraveling anthropogenic impact on Mawmluh Cave Speleothems: Insights from high-resolution analysis of aragonite formations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8998, https://doi.org/10.5194/egusphere-egu24-8998, 2024.

The Brujas cave is located in the eastern flank of the subtropical Andes, in the boundary between two major components of the climate system that drives precipitation variability over the South America: The South American monsoon system (SAMS) domain and the Southern hemisphere westerlies (SHW). As a result, the long-term hydroclimate variability in this region can be complex. Paleorecords from lake sediments and ice cores surrounding the area show meridional fluctuations of either the SAMS or the SHW, yet without long and high-resolution records, this area remains poorly constrained.

The deglacial and Holocene are interesting periods in this regard, providing valuable information about the atmospheric circulation in the western sector of SAMS in response to millennial-scale events of the last glacial. Moreover, changing climate forcings associated with ice volume and greenhouse gases can impact hydroclimate at these latitudes by reorganizing atmospheric circulation during the onset of the interglacial boundary conditions. For instance, the expansion of the Hadley cell under current global warming severely affects the regional hydroclimate of the mid-latitudes. Yet, our knowledge of this region is limited compared to what we know about the core SAMS region or the SHW in southernmost South America. New records from this transitional zone can provide clarity on the extent of variability in space and intensity of the SAMS and the SHW, serving as useful benchmarks to assess the performance of climate models in such a sensitive zone, right in interphase between two systems.

Here we present preliminary results from a stalagmite record (15,000 to 3,000 years) from Las Brujas cave, on the northern edge of the SHW domain. The westerlies transport moisture from the Pacific Ocean to the continent, where the Andes barrier induces orographic convection so that intense precipitation falls on the uphill side of the cordillera, over the Chilean Andes. The limited moisture that crosses the Andes and reaches the downslope area, produces precipitation over Las Brujas cave site during the cold months (April-September). Immediately north of Las Brujas cave, precipitation is concentrated in the warm season, produced by the South American low-level jet (SALLJ), a main component of the SAMS that transports moisture from the Amazon to northwestern Argentina. Given the proximity of both systems to our cave, precipitation contribution of either source is likely to have occurred in the past.  Our multiproxy record can potentially show periods of rainfall dominated by the SAMS or the westerlies and the relationship unveil local temperature variations. We find evidence of a slight trend from dryer to wetter conditions from the mid-Holocene onwards and a large shift from dry to wet from the deglacial to the early Holocene.

How to cite: Ampuero, A., Cruz, F., Strikis, N., Vonhof, H., Roig, F., Cauhy, J., Della Libera, M., Bernal, J. P., Utida, G., Medina, M., Vuille, M., Tejedor, E., Mayta, V., Ramirez, V., Piacsek, P., Schroeder, J., Cazelli, L., and Jaqueto, P.: Competing influence of the South American summer monsoon and the Southern Hemisphere westerlies on the mid-latitude Argentine Andes over the last 15,000 years as recorded in speleothems from Las Brujas Cave, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17100, https://doi.org/10.5194/egusphere-egu24-17100, 2024.

NW Türkiye is uniquely positioned between climatic influences from the North Atlantic, Mediterranean and Eurasia. Variability in climate systems through the Late Holocene is thought to have influenced major historical transitions, such as the ‘Bronze Age Collapse’, and during periods including the ‘Roman Climate Anomaly’ and the ‘Little Ice Age’. The region is noteworthy considering its geographical and historical significance over the last 4,000 years as a landscape for Ancient Greece Colonisation, the Roman Byzantine and Ottoman Empires and proximity to the common focal-point of modern-day Istanbul (Byzantium, Constantinople) which received much of its water from the cave’s locality. With the Eastern Mediterranean a hotspot for agricultural drought (Dabanlı et. al; 2017), which has impacted societies historically, the region warrants the study of spatio-temporal human-climate interactions.

Given the scarcity of sub-decadal palaeoclimate records regionally, and heterogeneity of Eastern Mediterranean climate generally (Jacobson et. al; 2021), stalagmite U-1 from Uzuntarla cave in Thrace helps fill this gap. Speleothem U-1 was dated using a combination of U/Th and ¹⁴C dates. The chronology is further refined by aligning distinct growth-shifts with well-dated and strong historical earthquakes. Using the combined evidence of calcite fabric and growth laminae changes, stable isotope (δ¹³C, δ¹⁸O), trace elements (Mg/Ca, Sr/Ca, P/Ca) and fluid-inclusion analysis, we find that U-1 is highly sensitive to changes in cold-season regional precipitation, seasonality and temperature. For example, increases in δ¹³C often coincide with narrowing of growth-laminae and increased Sr/Ca suggesting a unified influence by reduced drip-rate during poor recharge conditions. Effective infiltration is between Oct:Mar, making δ¹⁸O a combined indicator for Fall:Winter:Spring seasonality balance and temperature. Initial fluid inclusion temperature estimates are promising with work ongoing, however other factors are worth discussing such as aeolian oceanic Mg inputs. 

Initial results, often complimenting other regional palaeoclimate records, paints a picture of dynamic changes in climate over the last 3,900 years BP spanning key historical transitions. Speleothem U-1 describes a large shift in aquifer-recharge and seasonality preceding the Bronze Age Collapse impacting SW Asia around 1190 BCE. Recharge then peaks anomalously in 650-690 BCE during the Homeric Minimum, coinciding with the Greek Colonisation and Byzantium’s founding ~667 BCE. The acclaimed Roman Climate Anomaly (150 BCE-200 CE) is without wet-anomalies but stable for U-1, with later evidence of aridification. Wetter and stable conditions follow during 200-600 CE, a period encompassing defining historical events including the establishment of Constantinople as a powerhouse of the East Roman Empire and major infrastructure development including aqueduct expansion into Thrace. The Medieval Climate Anomaly (950-1250 CE) is defined by wet conditions during 760-1100 CE transitioning into lower aquifer recharge between 1100-1220 CE. Finally, the Little Ice Age (1400-1700 CE) shows highly variable conditions, but generally transitions from a wetter and colder period to lower aquifer recharge between 1220 and 1760 CE.

REFERENCES

Dabanlı et. al; 2017. Long-term spatio-temporal drought variability in Turkey. Journal of Hydrology, 552, pp.779-792.

Jacobson et. al; 2021. Heterogenous late Holocene climate in the Eastern Mediterranean—the Kocain Cave record from SW Turkey. Geophysical Research Letters, 48(20), p.e2021GL094733.

How to cite: Morgan, A., Cheng, H., Edwards, L. R., Matter, A., Hofmeister, E., Tüysüz, O., and Fleitmann, D.: A Late Holocene multi-proxy speleothem record from NW Türkiye, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17958, https://doi.org/10.5194/egusphere-egu24-17958, 2024.

Cova del Drac, situated on Mallorca Island, is one of the most frequented caves in Europe. During the late 19th century, pioneering explorers developed initial naturalistic expeditions and topographic studies. Nevertheless, it was not until the period between 1922 and 1935 that adaptation work was developed, leading to the establishment of permanent pathways, including the installation of the first lighting system. The two speleothems presented in this study were growing beyond these anthropogenic structures allowing a geochronological control into their initial growth.

The examination of confocal laser scanning microscopy images of these two speleothems revealed distinct fluorescence banding, pointing to seasonal growth patterns. Additionally, high-resolution trace element profiles, acquired using LA-ICP-MS, reveal geochemical cycles reflecting the impact of seasonal cave ventilation on the trace element signatures within the speleothems. Through the combination of annual fluorescence layer counting, analysis of trace element cycles, and the adjustment with the 14C bomb peak as a tie point, well-resolved age models spanning certainly the past century have been achieved.

This study establishes a robust framework by correlating the speleothem geochemistry results with cave monitoring and meteorological data. This exercise discerns the influence of the cave atmosphere seasonality from the hydrological and regional climatic signal across longer time scales. Consequently, this study validates the geochemical signal recorded in Mallorca cave speleothems as a reliable indicator of climatic variability in the western Mediterranean region.

How to cite: Torner, J., Cacho, I., Fornós, J., Català, A., Cisneros, M., Bladé, I., Moreno, A., and Stoll, H.: Decoding the climatic signal recorded in speleothems from La Cova del Drac in Mallorca, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19492, https://doi.org/10.5194/egusphere-egu24-19492, 2024.

The long-term trends of Holocene temperature obtained from reconstructions and simulations are inconsistent and have been controversial. Paleoclimate reconstructions suggest a gradual cooling after the Holocene climatic optimum, while model simulationss show continued warming. This is the long-standing Holocene conundrum. It is argued that some Holocene temperature reconstructions may be influenced by summer temperature bias. Therefore, finding proxy indicators less influenced by temperature seasonality is crucial in resolving the conundrum. Additionally, temperature reconstruction records in Southeast China are not yet comprehensive, the sensitivity of various proxies, uncertainties in chronology, and the uneven distribution of proxy records have led to significant differences in temperature reconstruction results. Stalagmites inside cave are in a relatively stable environment, and cave monitoring shows that the cave temperature is usually stable and represents the local annual mean temperature. Therefore, utilizing the water stable isotopes from stalagmite fluid inclusions can more accurately reconstruct local annual mean temperatures. This study used hydrogen and oxygen isotopes of three stalagmite samples (SN35, SN38, and SN42) from the Shennong Cave in Southeast China to reconstruct a temperature record for the Holocene (9 ka-0.8 ka). By employing a conversion function between calcite fluid inclusion water isotopes and annual mean temperature, we found the reconstructed cave temperature is ~19.1°C from 2-0.8 ka BP, consistent with the modern local annual mean temperature of 19.1°C, indicating these stalagmites could precisely record the local annual temperature changes. The reconstructed Holocene record shows a slight overall upward trend during the period of 9-0.8 ka BP, in agreement with model simulation results. The records also show a significant drop in temperature around 5.2 ka BP and a further abrupt change in temperature around 4.2ka BP, which may have had an important impact on the origin and decline of Liangzhu, a well-developed neolithic culture in the lower reaches of the Yangtze River.Our new record provides new evidence to resolve the Holocene temperature conundrum.

How to cite: Liang, Z., Zhang, H., Tian, Y., Cheng, H., Spöt, C., Cai, Y., Zhang, R., Zong, B., and Ning, Y.: Holocene temperature changes in southeastern China reconstructed from stalagmite fluid inclusions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7110, https://doi.org/10.5194/egusphere-egu24-7110, 2024.