CL1.2.3

South Africa has an extraordinary record of human evolution spanning the last ~3 million years, from the fossil remains of our early pre-human relatives in the Cradle of Humankind World Heritage site, through to more recent evidence for the emergence of modern humans. Common to almost all these sites are the presence of carbonate deposits, be they caves, rock shelters or open-air sites. Knowing how old the sites are, understanding the depositional environment and the potential to use the carbonates as records of past hydroclimate variability has motivated many years of research into them. While U-Th dating is a precise, robust, and very useful chronometer in human evolution, the biggest breakthroughs in the last decade have come from U-Pb dating. However, aspects of this chronometer remain a challenging analytical exercise, more-so as the technique becomes routinely applied to carbonates with less-than-ideal U/Pb ratios.

Here we present insights into both the U and Pb concentrations, distributions, and isotope ratios, from a relatively large U-Pb dataset ranging from ~3 Ma to just under 1 Ma. We divide the U-Pb ages into three categories defined by the % error on the U–Pb age (the good, the bad and the ugly), and use thin section petrography and laser ablation trace element transects through the flowstones to investigate the factors controlling the quality of the ages. Our data confirms the expected negative exponential relationship between U–Pb age and 234U/238U. There is no apparent relationship between U concentration and residual 234U/238U, suggesting U concentration patterns are controlled by 238U, not 234U. We show that variability in the amount of inherited Pb across the sampling layer (average variability of 63% relative to sample average) – not uranium (23% variability) or by extension radiogenic Pb – is a main factor controlling the resulting isochron’s quality.

The thin section petrography reveals all flowstones have undergone heavy diagenesis, the dominant fabric consisting of mosaic calcite with relic aragonite. However, we argue that the trace element signals, the abrupt, sympathetic step-like variation is Sr, U and in some cases Ba and Mg, indicate that this diagenesis is conservative. We do show what a completely recrystallized flowstone looks like, where the original trace element signals are completely obliterated, and it is impossible to resolve a U–Pb age. We identify a mixture of crystal and fluid dominated patterns, both of which are ultimately related to flow dynamics, in turn related to changes in external hydroclimate.

We look forward to future development in in situ laser ablation U-Pb dating, which will allow for even more material to be dated. There is great potential to extract valuable palaeoclimate records out of these old, U–Pb dated flowstones, which would be very interesting given their association with important early human evolution sites in South Africa. We predict these two areas will see rapid development in the coming years.

How to cite: Pickering, R., Engel, J., and Edwards, T.: The good, the bad and the ugly: 20 years of U-series dating carbonates from South Africa., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8103, https://doi.org/10.5194/egusphere-egu22-8103, 2022.

Tremendous progress has been made in the research on mechanisms modulating the dead carbon fraction (DCF) in speleothems, but the causes for high spatial and temporal variability of DCF in different climate zones are still not understood. We have chosen a predominantly hydroclimate-driven environment in the tropics to assess the variability of the DCF and to attempt to reveal the key governing processes. Our high-resolution ¹⁴C record obtained from a ²³⁰Th/U-dated stalagmite from Larga Cave, Puerto Rico, covers large parts of the last glacial between 41 ka and 12 ka before present (BP), as well as the past 400 years BP in the Holocene. Moreover, hydroclimate variability is resolved through trace metal ratios (e.g. Mg/Ca) and stable oxygen and carbon isotope records (δ¹⁸O and δ¹³C).

The stable isotopes and Mg/Ca time series exhibit a relatively stable mean state indicative of a generally constant hydroclimate (wet vs. dry) and a superimposed correlated variability on the millennial scale. On the contrary, the DCF values are extremely variable on a large range, from 20% to more than 50%. The DCF data indicates that the carbon cycling switches on a sub-centennial time-scale between three apparent modes: a maximum host rock dominated level around 50%, a more soil carbon driven mode around 25%, and an intermediate state in the range of 35%. Notably, this high variability seems to be absent in the Holocene growth period. However, DCF data of another stalagmite from the same cave at a significantly more ventilated location suggest relatively stable DCF values of 15-25 % throughout the glacial period.

With our multi-tracer record from Larga Cave, Puerto Rico, we will discuss the possible dominant processes causing the oscillation between the aforementioned distinct modes of carbon cycling. The comparison to records from the same cave and other locations in the area will disentangle local karst processes and hydroclimate influences on both spatial and temporal scales.

How to cite: Gafriller, J., Therre, S., Schorndorf, N., Warken, S. F., Keppler, F., Friedrich, R., Vieten, R., Mielke, A., and Frank, N.: Extreme sub-centennial Dead Carbon Fraction variability in a predominantly hydroclimate-driven environment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11642, https://doi.org/10.5194/egusphere-egu22-11642, 2022.

[1]D. Rudzka et al., (2011), GCA 75, 4321-4339.

[2] C. Welte, et al., (2016), Anal. Chem. 88, 8570– 8576.

[3] C. Welte et al., (2021), Clim. Past 17, 2165–2177.

[4] J. Fohlmeister et al., (2013), The Holocene 23, 749-754.

How to cite: Welte, C., Fohlmeister, J., Wertnik, M., Eglinton, T. I., and Spötl, C.: Radiocarbon and stable C isotope variability of two Holocene stalagmites from the high-alpine Spannagel Cave, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3454, https://doi.org/10.5194/egusphere-egu22-3454, 2022.

The transport and incorporation mechanisms of radiocarbon (¹⁴C), stable carbon isotopes (δ¹³C) and trace metal ratios into speleothems have been investigated intensively in the past. This provides a crucial understanding for the detection of climate and ecosystem signals (precipitation, vegetation variability) or even changes in atmospheric composition like radionuclide concentration. The Dead Carbon Fraction (DCF) in tropical settings often revealed a positive correlation with hydrological proxies, highlighting its relation with the amount of soil water infiltration. In contrast, more arid regions can have dominant aged stocks of soil organic matter (SOM) diluting the ¹⁴C concentration of the soil CO₂, which is responsible for an enhanced decoupling between speleothem DCF and hydrological proxies.

Here, we present a compilation of several new and published stalagmite ¹⁴C records in context with the predominant climatic parameters controlling their carbon signature. The records cover humid, tropical climates in Puerto Rico, temperate settings in Northern Turkey, as well as semi-arid alpine caves, and arid locations on the Arabian Peninsula. The range of mean DCF values is extreme, from below 10 to more than 60 % with δ¹³C values between -10 and 0 ‰. Climate-controlled mechanisms like the sensitivity of vegetation to net-infiltration changes are revealed, especially for more arid regions where aged SOM significantly contributes to stalagmite geochemistry.

In a first application, we revisit a published multi-proxy glacial record of a stalagmite from Socotra Island, which allows us to disentangle the increasing soil infiltration towards Termination I and the resulting long-term DCF trends. This is achieved by exploiting the correlation of a humidity proxy (Mg/Ca) with DCF and implementing a transfer function to correct for soil carbon effects in ¹⁴C.

Our approach hints at vast opportunities to better understand the control mechanisms in stalagmite carbon signature and correct for climate-induced effects. Therefore, it can aid future research in the search for stalagmite records which trace, for instance, atmospheric nuclide signals or bear unresolved climate-related trends.

How to cite: Therre, S., Fohlmeister, J., Warken, S. F., Schröder-Ritzrau, A., Friedrich, R., and Frank, N.: Disentangling climate-dependent stalagmite proxies using radiocarbon timeseries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4875, https://doi.org/10.5194/egusphere-egu22-4875, 2022.

Multiple factors control δ¹³C values in speleothems and complicate their paleoclimatic and paleoenvironmental interpretation. Therefore, most studies avoid the presentation of δ¹³C values, and instead, focus only 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 community and climate modelling.

As a first approach, we review the δ¹³C values for the last two millennia and evaluate the environmental influencing factors on 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 due to changes in the local hydroclimate and, to a minor extent, in 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 is responsible for a considerable lowering of δ¹³C values (≤6‰) in most of the speleothems.

How to cite: Novello, V. F. and Rehfeld, K. and the South American Speleothem Group: Investigating δ13C values in stalagmites from tropical South America, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1057, https://doi.org/10.5194/egusphere-egu22-1057, 2022.

The interpretation of paleoclimate records from speleothems remains a challenging task due to the individual characteristics of each specimen and cave system. Through recent advances in techniques like confocal microscopy and high-resolution geochemical analysis, fluorescent layers in speleothems have become a significant source of information to enhance paleo-seasonal reconstructions, improve age models and, consequently, constrain rates of past climate changes. In this framework, speleothem fluorescence originates from organic matter produced in the soil above the cave, from ancient organic compounds in the bedrock or from microbial processes within the karst. However, the mechanisms leading to the incorporation of fluorescent banding into calcite as well as the properties of transport, storage and decomposition of organic matter in natural karst systems are still under debate. We present results from a one-year monitoring study of fluorescence properties in drip water, sampled from May 2020 to May 2021 in a quasi-monthly resolution at 3-6 locations within the cave system La Vallina in Northwestern Spain. We have measured absorbance spectra and fluorescence exitation-emission matrices; and compare it to drip water geochemistry, fluorescence of active speleothems at the same site and vegetation type above the cave. Our results indicate high gradients of fluorescent properties in drip waters already on a small spatial scale. In the site where active speleothems show fluorescent banding, a humic-like fluorescent signal prevails in cave waters (AC peak, according to Coble nomenclature), while other sites are more likely to be influenced by microbial activity (B/M peak). Humic-like fluorescence is stronger in drip waters during the autumn season, probably due to the increased input by colloids. Yet, simple relationships between the fluorescence in drip water and colloid-associated trace elements like Cu and Y cannot be confirmed. Further, the difference in drip water fluorescence is small compared to the actual intra-seasonal difference retrieved by confocal microscopy in active stalagmites. Therefore, we find drip water composition unlikely to be solely responsible for seasonal enriched fluorescence incorporation in speleothems and favour conceptual models taking moisture-limitation and adsorption into account.

How to cite: Endres, L., Jacquin, C., Traber, J., Gonzàlez-Lemos, S., Rodriquez-Rodriquez, L., Sliwinski, J., Kaushal, N., Kost, O., and Stoll, H. M.: New insights from fluorescent organic matter in natural cave systems and active speleothems: a one-year monitoring study from Northwestern Spain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8035, https://doi.org/10.5194/egusphere-egu22-8035, 2022.

Terrestrial ecosystems, including soil and the biosphere, represent important reservoirs of carbon sources and cycling (IPCC, 2000). However, the reaction of terrestrial ecosystems to the changing climate remains poorly constrained. Over the past 20 years, interest in the organic matter (OM) fraction of speleothems, typically comprising 0.01-0.3% of the total carbon (Blyth et al., 2016), has increased due to its potential to offer information about past ecosystems. The sources of speleothem OM are not fully understood and are likely to be a combination of contributions from overlying vegetation, soil, microbial activity within the karst system, and cave fauna. Due to the link that the inner cave environment has with the karst, the signal of non purgeable organic carbon (NPOC) sourced from the overlying soil, vadose zone, or within the cave itself may be preserved within speleothems (Blyth et al., 2013). Hence, the isotopic characterisation (𝛿¹³C and ¹⁴C) of stalagmite NPOC has the potential to give information about past ecological and climactic state of the surrounding region (Blyth et al., 2013).

Presented here are the first results of a high-resolution process study of organic and inorganic carbon fluxes in the Milandre cave (Switzerland), whereby the main carbon source reservoirs will be monitored for two years. The total organic carbon content of cave waters ranges from 0.6 -1.3mg/L. The 𝛿¹³C of CO₂ in gas samples from atmospheric air (-9.24 ‰), soil air (-12.68 - -27.20‰), gas well air (-24.97- -25.78‰), and cave air (-14.29 - -25.32‰) were analysed. The soil air, well air and cave air have 𝛿¹³C values which range from close to atmospheric 𝛿¹³C to the most 𝛿¹³C depleted cave air end member which suggests differing levels of gas mixing throughout the system. Ultimately, this information will be used to constrain the source of speleothem NPOC and allow the assessment of its suitability as a proxy for ecosystem change.   

Blyth, A., Hartland, A. and Baker, A., 2016. Organic proxies in speleothems – New developments, advantages and limitations. Quaternary Science Reviews, 149, pp.1-17.

Blyth, A., Smith, C., and Drysdale, R., 2013. A new perspective on the 13C signal preserved in speleothems using LC-IRMS analysis of bulk organic matter and compound specific stable isotope analysis. Quaternary Science Reviews, 75, pp. 143-149.

IPCC, 2000: Land Use, Land-Use Change and Forestry. (R.Watson, I.Noble, B Bolin, N.H. Ravindranath,D.J. Verardo and D.J. Dokken (eds.)).  Cambridge University Press, UK, pp.375

How to cite: Rowan, S., Luetscher, M., Szidat, S., and Lechleitner, F. A.: High Resolution Monitoring of Organic Matter at Milandre Cave, Switzerland. Implications for Future Paleoecosystem Proxies., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4066, https://doi.org/10.5194/egusphere-egu22-4066, 2022.

Temperature in the inner section of most caves (i.e., away from well ventilated entrance sections) is controlled by external air temperature transferred underground by heat conduction. The key parameter that controls heat conduction is the thermal diffusion coefficient, that is specific for different materials. Although thermal diffusion coefficients can be calculated for specific carbonate rocks, the underground karst is not composed exclusively of bedrock since dissolution creates large pores and conduits filled with air and water that greatly impact thermal diffusion coefficients.  

We studied a 5-year temperature record of the entrance of Los Pilones Cave, in central Spain. The cave entrance is a sub-horizontal and meandering crawlway that limits the advection even in winter, making this cave ideal to study thermal conduction processes. Cave temperature was recorded along the 30 m section from the entrance by 10 TINITAG thermistors and external temperature was measured at ground and 2 m elevation levels. The thickness of bedrock cover above the cave was measured with a DISTO2 laser meter equipped with compass and clinometer providing uncertainties <0.05m.

The bedrock cover above the ceiling of the cave ranges from 8 to 15 m and all cave temperature records show annual thermal oscillations with different amplitudes and lag times in relation to the external annual thermal cycles. Cave temperature measurements support that heat conduction is the main heat transfer mechanism controlling cave temperature variability. Thermometers located under a thicker bedrock cover record less thermal amplitude of the annual signal and enhanced delays. The thermal diffusion coefficient was calculated from averaging the results from the thermal anomaly recorded at different depths and the lag time recorded at different depths. The dispersion of regression analyses (r²>0.9) is large compared to analyses performed on non-karst bedrocks, supporting the existence of local heterogeneities in the underground karst. We also noticed that the lag times of individual loggers changed during the studied period (interannual variability), which can be attributed to variable ratios of water saturation in the local porosity. Therefore, when reporting the thermal diffusion coefficient of karst terrains, their triphasic nature (i.e., rock, water and air) should be considered. So, the average thermal diffusion coefficient of a specific cave could vary in space or time beyond calculated uncertainties depending variable hydrological conditions.

Acknowledgements:

The project leading to this research has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No.101030314.

How to cite: Domínguez-Villar, D., Krklec, K., and Sierro, F. J.: The peculiar nature of thermal diffusion coefficients in karst terrains and their control on cave temperatures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2048, https://doi.org/10.5194/egusphere-egu22-2048, 2022.

Fabrics, trace element partitioning and stable isotope ratio fractionation into speleothem calcite depend on crystallization processes. We documented that in warm and wet tropical climate settings, high supersaturation and pH may shift from layer growth to nanoparticle/nanocrystal attachment. This suggests that both classical and non-classical growth mechanisms may be operating. We have observed that both non-classical amorphous calcium carbonate (ACC) nanoparticle or even nanocrystal attachment and spiral (classical) growth occur in calcite farmed in the caves of Atiu (Cook Island Archipelago).  Depending on localized shifts in SI_cc and pH, “impurities” may be preferentially incorporated as non-monomer species (non-classical) or monomer (classical) species. This gives rise to “random” lateral distribution of some trace elements that would otherwise be expected to follow the classical “sector zoning” pattern.  The “random” distribution is typical of porous columnar fabric, whilst the sector zoning distribution in Sr characterizes compact columnar calcite. In the porous columnar calcite fabric, the occurrence of non-classical ACC particle attachment also influences the stable oxygen isotope composition of its fluid inclusions, which is more negative than expected from dripwater (Global Meteoric Water Line) values. In the compact columnar fabric, there is not enough fluid inclusion water for measurements.

When applied to Sr incorporation, our findings suggest that its uptake into speleothem calcite is a function of SI_cc and pH (which influence non-classical pathways) rather than growth rate, as already hypothesized by Wasylenki et al. (2005). However, by having in mind only a classical crystallization mechanism, SI_cc becomes a measure of growth rate. Consequently, the argument of Wasylenki et al. (2005) would not explain why Wassenburg et al. (2021) did not find a relation between Sr uptake and stalagmite growth rate. If SI_cc is taken as a measure of the transition from monomer-by-monomer to ACC nanoparticle attachment, then Sr uptake becomes dependent on processes that govern the transformation from ACC to calcite at the site of attachment. The presence of growth inhibitors (inorganic and organic) that may be incorporated as non-monomer species and observed in Atiu’s speleothems, may explain why Sr uptake may either depend on growth rate or not, as well as its lateral heterogeneous variability. Ultimately, in porous columnar fabric, Sr uptake is dictated by both non-classical pathways and the presence of growth inhibitors incorporated as non-monomers.

References:

Wassenburg, J.A., Scholz, D., Jochum, K.P., Cheng, H., Oster, J., Immenhauser, A., Richter, D.K., Haeger, T., Jamieson, R.A., Baldini, J.U.L. and Hoffmann, D., 2016. Determination of aragonite trace element distribution coefficients from speleothem calcite–aragonite transitions. Geochimica et Cosmochimica Acta, 190, pp.347-367.

Wasylenki, L.E., Dove, P.M. and De Yoreo, J.J., 2005. Effects of temperature and transport conditions on calcite growth in the presence of Mg2+: Implications for paleothermometry. Geochimica et Cosmochimica Acta, 69(17), pp.4227-4236.

How to cite: Frisia, S., Borsato, A., Faraji, M., Hartland, A., Demeny, A., and Drysdale, R. N.: Crystallization pathways in stalagmites from the South Pacific: implications for fabrics and Sr uptake, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13200, https://doi.org/10.5194/egusphere-egu22-13200, 2022.

Carbon, oxygen and clumped isotope (Δ₄₇) values were measured from recently inactive travertine mounds located in Santovka and Dudince (Slovakia) to provide information about the origin of carbon, precipitation conditions, and paleotemperature. δ¹⁸O and δ¹³C analyses of carbonates were performed at the Institute for Geological and Geochemical Research (IGGR), Research Centre for Astronomy and Earth Sciences (Budapest, Hungary) and the clumped isotope analysis were performed at the Isotope Climatology and Environmental Research Center (ICER) of the Institute for Nuclear Research (Debrecen, Hungary). δ¹³C values show a range between +5.3‰ and +9.7‰ (V-PDB) and δ¹⁸O values (V-PDB) range between –11.2‰ and −7.5‰. These data are in accordance with the typical isotopic signature of thermogene travertines. Positive δ¹³C values also suggest that the thermal waters were charged with isotopically heavy CO₂ of deep origin, possibly produced through metamorphic reactions, as decarbonation of carbonate rocks. Calculated δ¹³C_CO2 values of −4.2% to −0.9‰, more positive than values of CO₂ coming from the pure igneous source possibly, support this suggestion. Mineral and thermal waters in Slovakia are mainly observed in the Inner Carpathians depressions and lowland, making the most plausible carbon sources as being the Triassic limestones and dolomites, where the aquifers were formed. Clumped isotope composition (Δ₄₇) of the inactive Santovka Mound and two inactive mounds from Dudince were measured. D_{47(CDES 25)} values range from 0.646 ± 0.012‰ and 0.717 ± 0.010‰, corresponding to temperature estimates (T(Δ₄₇)) that range from 17°C to 43°C using the calibration of Petersen et al. (2019) and 12°C to 33°C, using Kele et al. (2015) calibration. Calculated paleotemperatures of the paleosprings are slightly higher than the present equivalents measured directly in thermal water wells from Santovka and Dudince (14.5 °C to 26.9°C). δ¹⁸O (V-PDB) of the travertine precipitating fluid was calculated using the T(Δ₄₇) data, giving values on the range of –11.1‰ and −5.8‰, while the δ¹⁸O_water values measured from thermal water well on Santovka and Dudince vary from –11.3‰ to 10.1‰ The observed difference in the δ¹⁸O_water values could be interpreted as the influence of the present-day precipitation (–10.4‰ to –8.7‰) on the waters on this region.

How to cite: Vieira, D., Rinyu, L., and Kele, S.: Stable and clumped isotope characterization of travertine spring mounds from Santovka and Dudince (Southern Slovakia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7556, https://doi.org/10.5194/egusphere-egu22-7556, 2022.

Stromatolites form by the close interaction between the microbial activity and the environment in a great range of depositional settings resulting in heterogeneous growth morphologies and fabrics. The link between morphological diversity and internal structure of stromatolites to environments is not straightforward due to the dual influence at all scales of biological and physico-chemical factors. Specifically, in low energy settings biological controls are the dominant in influencing stromatolites, as suggested from modern analogues.

In this study we examine geometries and fabrics of stromatolites from the mixed carbonate-siliciclastic marginal lacustrine succession of the Yacoraite Formation (Cretaceous-Paleogene) in Tres Cruces (Salta Basin). The outcrops that extend along a W-E transect of 10 kilometres, provide exceptional exposure allowing to analyse the geometries and lateral continuity of the stromatolite beds. Current stratigraphic research interprets the Yacoraite succession as a closed, saline lake with two evolutionary stages. The first stage, dominated by carbonate production, represents a shallow-water perennial lake with moderate wave energy. The second stage corresponds to a rapidly fluctuating, low-water energy ephemeral lake with abundant fine-grained siliciclastics and frequent subaerial events. This change is related to climatically driven lake-level fluctuations. Marked differences in the lateral continuity of the stromatolite beds and their associated facies have been observed along the Yacoraite succession. In the perennial lake, the stromatolite beds overlie oolitic facies and can be traced laterally for several kilometres whereas in the ephemeral lake the stromatolites grow on both oolitic and siliciclastic facies and form discontinuous levels along hundreds of meters that pass laterally into the oolitic facies. Stromatolite growth morphologies, however, show a more homogeneous distribution that does not clearly reflect the evolutionary changes of the Yacoraite paleolake. Generally, the stromatolites of the perennial lake exhibit planar morphologies that pass upwards into coalescent domes forming structures that range in height from few decimetres up to 1 m. The stromatolites of the ephemeral lake are mainly planar, wavy (dm-scale) or domes that are coalescent and form tabular decimetric structures. Morphological vertical zonation is rare. The change in stromatolite morphology can be tentatively attributed to decreased accommodation and water energy conditions. However, this interpretation needs to be taken carefully considering that all these types of stromatolite morphologies have been observed along the Yacoraite succession, regardless of the lake stage. Stromatolites show mainly well-developed internal lamination. Their microfabrics are either fine-grained (micritic, clotted and/or filamentous) or formed by combinations of fine-grained and sparry layers composed of fibrous calcite crusts, calcite spherulites and/or shrubs.

Further work will intend to better understand the spatial and temporal distribution of the stromatolite geometries and fabrics along the Yacoraite Formation to shed light on the influence that environmental and biotic factors exert in stromatolite macro, meso and microscale in low-energy lacustrine settings.

How to cite: Tomás, S., Vallati, M., Galli, C., and Mutti, M.: Are stromatolite morphologies and fabrics good paleoenvironmental proxies? An example from the Salta Basin (Argentina), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11997, https://doi.org/10.5194/egusphere-egu22-11997, 2022.

For many years, there have been ongoing works on modelling the growth processes of stalagmites to obtain climatic information from their shape and stratigraphy. However, knowledge is still limited and it is therefore essential to improve our understanding of the underlying processes. Several studies focus on developing new algorithms to describe the equilibrium radius and the growth rate (Romanov et al., 2008) but there are only a few attempts to drive the Shape Model with time series. Kaufmann for example, focuses on the temperature as the driving force for growth variations (Kaufmann, 2003). Here, we introduce a coupling of three existing models in order to simulate the shape and growth rate of the So-1 stalagmite from the Sofular Cave in Northern Turkey. 

The presented Shape Model only needs 4 input parameters to simulate the stalagmite: cave temperature, calcium concentration of the water drop, drip rate and the CO₂ concentration in the cave. To determine these values we use modelled data from the Max Planck Institute Earth System Model version 1.2 (MPI-ESMI1.2) and ice core data. Additionally, we use CaveCalc, a numerical model for speleothem chemistry and isotopes, to calculate the chemical reactions in the soil and karst above the cave. Through this approach we were able to simulate a stalagmite, which follows the trend of the experimental data for the growth rate, using the input parameters inside the respective error ranges. Real-world growth variations under 5 kyr are not visible. Furthermore, the effect of the individual parameters can be tested. Here, the model suggests that the radius mainly depends on the drip rate, whereas the growth rate is driven by the calcium concentration of the water drop. The model is also capable of showing some basic principles like a decrease in height as the distance to the entrance and hence CO₂ concentration increases.

This new coupling opens the possibility of adjusting the data till the model corresponds better to the experimental data in order to get insights into difficult values like the drip rate. Further, it can be the start for a new inverse approach by calculating which input values correspond to the measured data while keeping some parameters fixed.

References:

Romanov, D., Kaufmann, G., and Dreybrod, W. (2008). Modeling stalagmite growth by first principles of chemistry and physics of calcite precipitation.
Geochimica et Cosmochimica Acta, 72(2):423–437.

Kaufmann, G. (2003). Stalagmite growth and palaeo-climate: the numerical perspective. Earth and Planetary Science Letters, 214(1-2):251–266

How to cite: Merz, N., Hubig, A., Kleinen, T., Kaufmann, G., and Frank, N.: Does a real-world speleothem look like the prediction: A comprehensive study of the Sofular Cave, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9784, https://doi.org/10.5194/egusphere-egu22-9784, 2022.

Speleothem archives (cave carbonates) are widely distributed in terrestrial regions, and provide highly resolved records of past changes in climate and vegetation encoded in the oxygen and carbon isotope proxies. The SISALv2 database, created by the PAGES-SISAL Phase 1 Working Group, provided 700 speleothem records from 293 cave sites, 500 of which have standardized chronologies. The database provides access to records that were hitherto unavailable in the original publications and/or repositories, and has enabled regional-to-global scale analysis of climatic patterns using a variety of approaches such as data-model comparisons. 

The PAGES-SISAL Phase 2 Working Group is a continuation of the previous efforts to index speleothem datasets, focusing on the following objectives: (i) exploring ways to synthesise modern cave monitoring data to provide robust modern baselines and improve proxy interpretations, (ii) adding trace element proxies of Mg, Sr, Ba, U, and Sr isotopes to the SISAL database to increase our understanding of regional climatic variability, (iii) a database-update to incorporate ~100 identified speleothem datasets that are currently not in the database, (iv) providing a javascript web app with a user-friendly GUI to increase SISAL data accessibility.

Here, we present preliminary information on available cave monitoring metadata synthesized from the Cave Monitoring Database (product of a Cave Monitoring workshop in Innsbruck, Austria) and published speleothem trace element records, highlighting regions where overlapping stable isotope, trace element and monitoring datasets are available, and identifying gaps. We show the proposed database structures for cave monitoring and speleothem trace element data, linking them to the speleothem entities in the existing SISAL database with persistent identifiers, and introduce the Beta version of the SISAL GUI. We briefly present a synopsis of the SISAL-community level discussions on best practices for reporting trace element data, and reducing data measured with high resolution laser ablation methods. 

We welcome feedback on PAGES-SISAL Phase 2 activities listed above, and encourage participation and collaboration from interested researchers in different stages of their academic career and working in different geographical regions and allied disciplines.

How to cite: Kaushal, N., Lechleitner, F. A., Tanos, P., Hatvani, I. G., Kern, Z., Wilhelm, M., Burstyn, Y., and Baker, A.: SISAL speleothem database updates - link to modern monitoring data, additional proxies and increased accessibility, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1576, https://doi.org/10.5194/egusphere-egu22-1576, 2022.

To reliably predict future changes, it is crucial to understand the response of the climate system to past changes in radiative forcing, which are investigated using climate models as well as information extracted from paleoclimate archives such as speleothems. Hydrological changes in past, present, and future are, however, far less understood and more uncertain than changes in temperature.

Speleothems are terrestrial archives in the low to 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, speleothem inherent features, such as growth hiatuses or large and abrupt changes in growth rates, are a challenge for current age-depth modelling methods.

Here, we compare modelled precipitation amount from the Paleoclimate Modeling Intercomparison Project (PMIP), in particular 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 large 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). Comparing the simulated changes with speleothems selected from SISALv2 according to these criteria can thus help to constrain past precipitation changes and subsequently confine uncertainty of future changes.

How to cite: Buehler, J., Roesch, C., Weitzel, N., Scholz, D., Comas-Bru, L., and Rehfeld, K.: Last Glacial Maximum to present day precipitation changes from speleothem growth rates and in climate simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-318, https://doi.org/10.5194/egusphere-egu22-318, 2022.

Abrupt events punctuate the climate of the Holocene epoch, providing valuable insight into rapid climate change. The most notable abrupt event of the Holocene was the 8.2 ka event, when a large influx of meltwater into the North Atlantic reduced northward heat transport in this region. The event provides valuable insight into the global climate response to North Atlantic freshening. Here, we examine the timing, duration and magnitude of the climate response using a global network of speleothem oxygen isotope (δ¹⁸O) records.

Firstly, we objectively identified abrupt climate events in 402 globally distributed speleothem records from the SISAL (Speleothem Isotopes Synthesis and AnaLysis) database (Atsawawaranunt et al., 2018; Comas-Bru et al., 2020) during the Holocene. Secondly, we examined the timing, duration and anomalies of the 8.2 ka δ¹⁸O excursions using 70 speleothem δ¹⁸O records.

We show that the 8.2 ka event is the most globally coherent and significant abrupt event of the last 12,000 years, with an abrupt δ¹⁸O excursion identified in >70% of speleothem records. The δ¹⁸O anomalies are regionally homogeneous; they are negative across Europe and the Mediterranean, positive across Asia, and negative in South America and southern Africa. The excursion is not registered in the Indonesia/Australia region. The median timing of the event from the speleothem records is 8223 ±12 to 8062 ±14 years BP, indistinguishable from the timing in Greenland ice cores of 8247 to 8086 ± 47 years BP (Thomas et al., 2007). The median duration of the 8.2 ka event excursion in speleothems is 159 ±11 years, indistinguishable from the duration in Greenland of 160.5 ± 5.5 years (Thomas et al., 2007). There is no significant difference between the timing and duration in regions both near (Europe) and far (Asia) from the North Atlantic. This globally synchronous timing and duration supports a rapid and widespread climate response, likely via rapid atmospheric teleconnections.

Atsawawaranunt, K., et al., 2018. The SISAL database: a global resource to document oxygen and carbon isotope records from speleothems. Earth System Science Data, 10(3), pp.1687-1713.

Comas-Bru, L., et al., 2020. SISALv2: a comprehensive speleothem isotope database with multiple age–depth models. Earth System Science Data, 12(4), pp.2579-2606.

Thomas, E.R., Wolff, E.W., Mulvaney, R., Steffensen, J.P., Johnsen, S.J., Arrowsmith, C., White, J.W., Vaughn, B. and Popp, T., 2007. The 8.2 ka event from Greenland ice cores. Quaternary Science Reviews, 26(1-2), pp.70-81.

How to cite: Parker, S. and Harrison, S. P.: The timing, duration and magnitude of the 8.2 ka event in global speleothem records, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3953, https://doi.org/10.5194/egusphere-egu22-3953, 2022.

This research is based on broader study investigating drivers of decadal to centennial-scale variations in the Central American Monsoon (CAM), a sub-region of the broader North American Monsoon. In the context of the Global Monsoon system, the precipitation patterns of CAM are of particular interest because of the placement/shifting of the ITCZ through time, its proximity to the AMOC system, and that existing precipitation records from this area have revealed a heterogenous pattern throughout the past 2 kyr.

Here we present new carbon and oxygen isotopic records of two speleothems, MO-AL-3 and MO-CU-2, recently collected from Mona Island, Puerto Rico. These speleothems together cover the last 2 kyr BP, thus significantly expanding the hydrologic history of the Northeastern Caribbean from speleothem records. Previous studies, mostly from the Western Caribbean, have revealed that Caribbean SSTs as well as solar and volcanic forcing are involved, to different degrees, as driving mechanisms determining the strength of the InterAmerican monsoon systems over the late Holocene. The study of precise, independent chronologies extracted from speleothems, and comparing them to local and regional coral/sclerosponge SST reconstructions, allows for an improved understanding of precipitation patterns of the Caribbean overtime. This new record allows the investigation of decadal to centennial-scale precipitation variability, as well as its linkage to past human civilizations. There is also potential to contribute to the recent discussion of whether the AMO is an internal oscillation or externally forced.  

How to cite: Cozadd, C., Lachniet, M., Warken, S., Li, H., and Winter, A.: Does Caribbean SST drive decadal to centennial-scale variability in the Central American Monsoon? Evidence from stalagmites from Mona Island, Puerto Rico, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8933, https://doi.org/10.5194/egusphere-egu22-8933, 2022.

We reconstructed changes in summer and winter precipitation using a well-dated (±18 years 2σ error) speleothem spanning 4.2-3.1 ka BP from Dharamjali Cave in the central Himalaya. The record was sampled at a sub-annual resolution for a suite of trace elements, as well oxygen and carbon stable isotopes. Calcium isotopes at decadal resolution provide additional hydroclimatic evidence. This DHAR-1 stalagmite records a 230-year period of increased drought frequency in both the summer and winter seasons after 4.2 ka BP, with aridity events centered on 4.19, 4.11 and 4.02 ka BP each lasting between 25 and 90 years. The data after 3.97 ka BP support a recovery in summer monsoon rainfall, peaking around 3.7 ka BP. The significance of this new record includes remarkable coherence between the moisture proxies over 4.2-3.97 ka BP in a well-dated record, which provides confidence in the duration of droughts and timing of monsoon recovery. It also places seasonal climate variability on a timescale relevant to human decision-making, which is particularly significant for this region nearby the Indus River Basin. The Indus Civilization reached its urban apex by 4.2 ka BP, and archaeologists have documented a shift in settlement locations, population, health, and agricultural strategies thereafter for a period of several centuries. This stalagmite record provides valuable insights into seasonal precipitation availability during a critical climatic and cultural transition phase.

How to cite: Giesche, A., Hodell, D. A., Petrie, C. A., Haug, G. H., Adkins, J. F., Plessen, B., Marwan, N., Bradbury, H. J., Hartland, A., French, A. D., and Breitenbach, S. F. M.: Northwest Indian stalagmite shows evidence for recurring summer and winter droughts after 4.2 ka BP, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-396, https://doi.org/10.5194/egusphere-egu22-396, 2022.

Speleothemoxygen isotope records from East Asia have been utilized to reconstruct Asian summer monsoon (ASM) variability over the last several hundred thousand years. However, what the isotope variation represents on orbital to annual timescales remains greatly debated. The high-resolution speleothem records combined with modern meteorological observation are essential for better understanding this debate. Here, we report a stalagmite δ¹⁸O (δ¹⁸Oc) record of the highest resolution (average of ~1-yr) between 1730 to 8590 yr BP from Majiaping (MJP) Cave, Guizhou Province, southwest China. This record is precisely dated based on the ¹⁴C dating method combined with ²³⁰Th/U, ²¹⁰Pb, and lamination counting dating methods. The result shows that the ¹⁴C dating method can establish a reliable chronology for stalagmites that cannot be dated by ²³⁰Th/U. The comparisons of the precipitation δ¹⁸O with the local temperature, rainfall amount, and moisture sources show that the δ¹⁸Oc record from southwest China is mainly controlled by the “amount effect” on annual to decadal timescale modified by ENSO. The consistent long-term δ¹⁸Oc trends among all monsoonal regions in the low latitudes of the northern hemisphere indicate that on the orbital timescale the δ¹⁸Oc trend reflects changes in the large-scale spatial circulation of the atmosphere, which is controlled by the changes of northern hemisphere summer insolation. Ensemble Empirical Mode Decomposition (EEMD) and Bernaola-Galvan Segmentation Algorithm (BGSA) analyses reveal that on the semi-millennium timescale, the δ¹⁸Oc record of the MJP stalagmite shows 8 weak East Asian summer monsoon events during 8.2ka BP, 7.3 ka BP, 5.9 ka BP, 5.5 ka BP, 4.2 ka BP, 3.1 ka BP, 2.4 ka BP and 1.9 ka BP. The comparisons of the structural feature and forcing factor of the first 7 events with the 1.9 ka event indicate that the first 7 events correspond to the changes in total solar irradiance and the 1.9 ka event may be related to the internal forcing of the Earth system controlled by the ENSO. On the interannual-multidecadal timescale, the δ¹⁸Oc record shows the high-frequency cyclicities of 3~7-yr and 30~70-yr which are related to ENSO and PDO according to modern instrumental records. However, the relationships among ENSO, PDO, and the δ¹⁸Oc are not constant during the Holocene.

How to cite: Liang, M.-Q., Li, H.-C., Mii, H.-S., Ma, Z.-B., Li, T.-Y., and Löwemark, L.: Paleoclimatic evolutions during the Holocene: A stalagmite δ18O record from Majiaping Cave, Guizhou, China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3100, https://doi.org/10.5194/egusphere-egu22-3100, 2022.

Continental carbonates constitute an interesting topic of study since they are important archives recording climate and paleoenvironmental changes. In Tunisia, calcretes are formed during the Pliocene-early Pleistocene (Villafranchian). They mainly occur in the center and on the coastal plain of Djeffara (Southern East) while their presence is more sporadic in the North of the country. Continental carbonates may form in the soil, groundwater, and palustrine and lacustrine environments. Four criteria are used to differentiate these different environments: host rock, components and micromorphological texture, subaerial exposure (seasonality), and flora and fauna.

The purpose of this study is to investigate the palaeoenvironmental significance of Tunisian calcretes for the Plio-Pleistocene. For this aim, well-developed carbonate beds were studied along a north-south transect that crosses the climatic boundaries between the latitudes 33 ° and 37 ° N: North (N36º.43.713 E10º.06.681’) Center (N35º.07.077 'E10º. 14.545 ') and South (N33º.28.898' E10º.20.597 ').

Based on the macroscopic, petrographic, and cathodoluminescence observations in association with scanning electron microscopy results, we classified thin sections extracted from the massive horizons in all sites into 8 facies types:

The Northern site is characterized by 1) pisolithic calcretes and 2) laminar calcretes showing several beta microfabrics such as rhizolith, peloids, intraclasts, coated grains, bioclast debris, cracks, alveolar septal, spherulite, and organic matter. Moreover, 3) pseudo microkarst carbonates were detected in Northern Tunisia by the presence of vertical layers, peloids, intraclasts, circum crack grain, pedotubules, and rhizoconcretions, and bioclasts.

At the central site, 4) laminar calcretes are characterized by planar layers. Both 5) massive brecciated calcretes and 6) mottled nodular brecciated calcretes are distinguished by the abundance of cracks. All these facies types’ shows similar pedogenic components such as peloids, coated grains, gastropod shell, alveolar septal, ooids, and bioclasts.

The southern site is characterized on the one hand by 7) laminar calcretes composed of peloids, nodules, coated grains, cracks, and on the other hand by 8) groundwater nodules showing a massive aspect with alpha microfabrics. In all sites, the nodular horizons are pedogenic.

Thus, our Plio-early Pleistocene calcretes formed in three main depositional environments: pedogenic, groundwater, and palustrine. The groundwater calcretes are formed under phreatic conditions while the Tunisian pedogenic calcretes and palustrine carbonates exhibit subaerial exposure characteristics (cracks). Except for southern groundwater calcretes, all other types of carbonates show biogenic traces. The palustrine carbonates developed above lacustrine mud. Whereas, pedogenic and groundwater calcretes, develop on different types of host rocks (siliceous and clayey). The difference between fabrics indicates that during the Pliocene-early Pleistocene calcrete form in the north in palustrine settings while it forms in groundwater context in the south. Furthermore, the transition between the different environments is controlled mainly by variation in the water table suggesting a variable but generally more humid climate during the Plio-Pleistocene in North Africa.

How to cite: Jarraya, F., Mauz, B., Rogerson, M., Elmejdoub, N., Sghari, A., and Kallel, N.: Palaeo-environmental and palaeo-climatic significance of Tunisian calcretes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3106, https://doi.org/10.5194/egusphere-egu22-3106, 2022.

Speleothems from well-monitored Cloşani Cave (Romania), have provided excellent records of past rainfall amount and European winter hydro-climate variability (Warken et al., 2018). Here we present new data allowing to extend the precipitation history of Central-Eastern Europe back to the Last Glacial Maximum (LGM) as well as MIS 3. High-precision ²³⁰Th/U ages show that the two analysed speleothems (C09-1 and C09-2) grew nearly continuously during the past 20 ka, with only one growth interruption between c. 11 and 9.7 ka BP. In addition, C09-2 also covers the Dansgaard/Oeschger (D/O) Stadials/Interstadials 16 to 14 between 60 and 52 ka BP. Consistently with previous results, the speleothem proxies (δ¹⁸O and δ¹³C values, as well as laser ablation ICPMS trace element profiles) provide a comprehensive picture of local and regional hydro-climate variability on centennial to glacial/interglacial timescales.

Over the course of the record, all proxies reveal millennial-scale features associated with prominent transitions during MIS 3, i.e., D/O events 16 to 14, as well as during the deglaciation, i.e., the Bølling-Allerød (BA) and Younger Dryas (YD). Local wetness as indicated by Mg/Ca ratios exhibits large variability, including pronounced swings between dry conditions during MIS 3 interstadials, and wetter conditions during stadials. After speleothem growth re-initiated at 20 ka BP, Mg/Ca ratios indicate a progressive drying until 15 ka BP, followed by an interval with enhanced variability from the Late Glacial to the Early Holocene. During the subsequent mid to late Holocene, from 8 ka BP to present, the local hydroclimate was characterized by relatively stable conditions. This dataset thus provides new insights into Central-Eastern European precipitation variability, and possibly also into its linkages to the North Atlantic realm.

References:

Warken, S.F., Fohlmeister, J., Schröder-Ritzrau, A., Constantin, S., Spötl, C., Gerdes, A., Esper, J., Frank, N., Arps, J., Terente, M., Riechelmann, D.F.C., Mangini, A., Scholz, D., (2018). Reconstruction of late Holocene autumn/winter precipitation variability in SW Romania from a high-resolution speleothem trace element record. Earth and Planetary Science Letters 499, 122-133. DOI: 10.1016/j.epsl.2018.07.027

How to cite: Warken, S. F., Riechelmann, D. F. C., Fohlmeister, J., Schröder-Ritzrau, A., Spötl, C., Jochum, K. P., Scholz, D., Constantin, S., and Frank, N.: Multi-proxy speleothem records attest to Central-Eastern Europe hydro-climate variability during MIS 3, the LGM, and the Holocene, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4294, https://doi.org/10.5194/egusphere-egu22-4294, 2022.