Session CL1.1

[Programme]

CL1.1 | Novel and quantitative methods for reconstructing continental palaeoenvironments and palaeohydrology

Novel and quantitative methods for reconstructing continental palaeoenvironments and palaeohydrology

Convener: Ola Kwiecien | Co-conveners: Jessica Oster, Cindy De Jonge, Bethany Fox, Sebastian F.M. Breitenbach

Orals

| Tue, 25 Apr, 08:30–10:05 (CEST)

Room 0.49/50

Posters on site

| Attendance Tue, 25 Apr, 16:15–18:00 (CEST)

Hall X5

Posters virtual

| Attendance Tue, 25 Apr, 16:15–18:00 (CEST)

vHall CL

Over recent decades we have gained a robust understanding of climate change fundamentals, but its specific and localized impacts are anything but certain. The need to provide boundary conditions for forecasting and computational modelling has increased the importance of quantitative methods in the field of palaeoenvironmental, palaeoclimatic and palaeohydrological reconstruction.

Continental environmental archives (e.g. speleothems, lake and river sediments, peatlands, and vertebrate and invertebrate remains) are often highly temporally resolved (subdecadal to seasonal) and provide more direct information about atmospheric and hydrological processes than marine archives. The wide variety of continental archives allows for intercomparison and ground-truthing of results from different environments, while multi-proxy reconstructions from the same archive can disentangle local and supra-regional environmental conditions. This approach is particularly useful when dealing with high spatial variability, signal buffering, nonlinearities, and uncertainties in the proxy sensitivity.

This session aims to highlight recent advances in the use of innovative and quantitative proxies to reconstruct past environmental change on land. We welcome studies of all continental archives, including but not limited to carbonates (cave deposits, palaeosols, snails), sediments (lakes, peatlands, rivers, alluvial fans), and biological materials (tree rings, fossil assemblages, bones, biomarkers). If you calibrate physical and chemical proxies that incorporate modern transfer functions, perform forward modeling and/or geochemical modeling to predict proxy signals, or attempt at quantitative estimates of past temperature and palaeohydrological dynamics you are mostly welcomed in our session! We are keen to invite reconstructions of temperature and hydrologic variability over large spatial scales, palaeoclimate data assimilation and monitoring studies leading to calibration or simply better understanding of climate proxies. Our session provides a forum for discussing recent innovations and future directions in the for continental palaeoenvironmental studies on seasonal to multi-millennial timescales.

Orals: Tue, 25 Apr | Room 0.49/50

Chairpersons: Ola Kwiecien, Jessica Oster, Sebastian F.M. Breitenbach

08:30–08:35

5-minute convener introduction

08:35–08:55

EGU23-1447

ECS

solicited

On-site presentation

Temperature and precipitation reconstruction for Last Glacial Central Europe reveals new insights into continental climate dynamics

Charlotte Prud homme, Peter Fischer, Olaf Jöris, Sergey Gromov, Mathias Vinnepand, Christine Hatté, Hubert Vonhof, Olivier Moine, Pierre Antoine, Andreas Vött, and Kathryn Fitzsimmons

Over the last glacial period, the climate of the Northern Hemisphere experienced numerous abrupt variations on millennial to centennial timescales known as Dansgaard-Oeschger events. These events, characterised by rapid warming at the beginning of interstadials and gradual cooling back to stadial conditions are best documented in Greenland ice cores and North Atlantic marine records, while their propagation onto the continents and potential feedbacks are less well documented. In this context, loess palaeosol sequences in central Europe are valuable archives, often recording these climatic changes in the form of brown soils and tundra gley horizons - indicating milder interstadial conditions - intercalated with primary loess deposits reflecting cold stadial conditions.

To reconstruct palaeoclimate changes at high resolution we use singular material from loess sediments: fossil earthworm calcite granules (ECG). ECGs, composed of aggregated sparite crystals formed in the calciferous earthworm glands, are secreted daily at the soil surfacemostly by Lumbricus species and experience limited vertical mixing within the loess sedimentary column. ECGs are thus an excellent terrestrial material for palaeoclimate reconstructions using stable isotopic geochemistry and radiocarbon dating. ECGs have been collected from two temporally overlapping loess-palaeosol sequences along an NNW-SSE transect in the Rhine River valley of western Germany. We present warm-season land-surface temperature and precipitation estimates at millennial timescales spanning ~ 45-22 cal kBP (late OIS 3 - OIS 2). We demonstrate that OIS 3-2 climate in the Rhine Valley was significantly cooler during the warm season and overall drier with annual precipitation reduced by up to 70%, compared to the present day. Interstadials were only slightly warmer (1-4°C) than stadial indicating strong attenuation compared to Greenland records. In combination with mesoscale wind and moisture transport modelling we can show that this region was dominated by westerlies and thereby inextricably linked to North Atlantic climate forcing.

The approach combining high-resolution age-depth modelling and geochemical proxy-based climate reconstruction can be readily adopted at other loess palaeosol sequences. We envisage a widespread application of this approach that would improve our understanding of regional variability over the European continent in response to North Atlantic climate changes over millennial to centennial timescales.

How to cite: Prud homme, C., Fischer, P., Jöris, O., Gromov, S., Vinnepand, M., Hatté, C., Vonhof, H., Moine, O., Antoine, P., Vött, A., and Fitzsimmons, K.: Temperature and precipitation reconstruction for Last Glacial Central Europe reveals new insights into continental climate dynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1447, https://doi.org/10.5194/egusphere-egu23-1447, 2023.

08:55–09:05

EGU23-13521

ECS

On-site presentation

Cloudy with a chance it rained: Progress towards a proxy for palaeocloud

Tamara Fletcher, Julia Tindall, Jochen Voss, and Alan Haywood

Cloud has profound impacts on climate, thus accurate cloud simulation is critical for accurate climate modelling. As the greatest source of uncertainty in such models, cloud drives discrepancies in the prediction of future climate. Cloud simulations are validated against recent observations; however, these records do not capture the climate space we are entering this century, limiting our ability to test model accuracy under near future conditions.

The best analogue for the 21st Century climate trajectory comes from the Pliocene. Reconstructions of Pliocene cloud regimes would provide critical validation data for climate model performance with respect to cloud. However, despite the wealth ways to reconstruct other climate variables, no method has been developed for reconstructing cloud in deep time.

We are working towards proxies capable of reconstructing past cloud, with the goal of establishing a global cloud database for the Pliocene. Our initial results demonstrate the relationship between vegetation and large-scale patterns in cloud in the modern, and tests the model derived from the modern data against palaeoclimate model vegetation and cloud.

How to cite: Fletcher, T., Tindall, J., Voss, J., and Haywood, A.: Cloudy with a chance it rained: Progress towards a proxy for palaeocloud, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13521, https://doi.org/10.5194/egusphere-egu23-13521, 2023.

09:05–09:15

EGU23-10570

ECS

On-site presentation

Exploring Pacific Island hydroclimatic extremes using the South Pacific Drought Atlas

Philippa Higgins, Jonathan Palmer, Fiona Johnson, Martin Andersen, and Chris Turney

Droughts are a natural occurrence in many small Pacific Islands and can have severe impacts on local populations and environments. The El Niño-Southern Oscillation (ENSO) is a well-known driver of drought in the South Pacific, but our understanding of extreme ENSO events and their influence on island hydroclimate is limited by the short instrumental record and the infrequency of ENSO extremes. To address this gap, we present the South Pacific Drought Atlas (SPaDA), a multi-proxy, spatially resolved reconstruction of the November-April Standardised Precipitation Evapotranspiration Index for the southwest Pacific islands. The reconstruction integrates coral proxies, which provide local information on the South Pacific hydroclimate but are limited in number and length, with a network of continental tree-ring chronologies targeting Pacific climate variability through remote teleconnections. The reconstruction demonstrates the benefits of multi-proxy reconstructions incorporating tree rings, which allow for the alignment of other proxy records without chronological error.

The SPaDA provides a 350-year, continuous dataset of climate information, which can be used to explore the occurrence of extreme events in the pre-instrumental period. The SPaDA closes the gap between existing paleo-reconstructions of point ENSO indices, and a spatially resolved drought atlas, allowing both the hydroclimate of individual islands and regional patterns of drought to be assessed. The benefit of a spatially resolved dataset to assess climate extremes in small Pacific islands is highlighted in the case of extreme El Niño events, which can have substantially different hydroclimatic impacts than more moderate events.

We used an Isolation Forest, an unsupervised machine learning algorithm, to identify anomalous hydroclimatic states in the SPaDA that may indicate the occurrence of an extreme event. Extreme El Niño events characterised by very strong southwest Pacific drought anomalies and a zonal South Pacific Convergence Zone orientation are shown to have occurred semi-regularly throughout the reconstruction interval, providing a valuable baseline to compare to climate model projections. By identifying the spatial patterns of drought resulting from extreme events, we can better understand the impacts these events may have on individual Pacific Islands in the future.

How to cite: Higgins, P., Palmer, J., Johnson, F., Andersen, M., and Turney, C.: Exploring Pacific Island hydroclimatic extremes using the South Pacific Drought Atlas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10570, https://doi.org/10.5194/egusphere-egu23-10570, 2023.

09:15–09:25

EGU23-9130

On-site presentation

Retrieving the rainfall signature from the isotope composition of speleothem fluid inclusion water: progress and pitfalls

Hubert Vonhof, Monika Markowska, Elan Levy, Alfredo Martinez Garcia, Sam Nicholson, and Julian Schroeder

Over recent years, a growing number of case studies have highlighted the relevance of fluid inclusion (FI) isotope analysis on speleothem calcite for the reconstruction of rainfall isotope variation back in time. Multiple studies documented FI isotope results consistent with projected local meteoric water line values, demonstrating that FI isotope analysis can provide unique and quantitative paleohydrological data. Several other studies have shown that FI isotope data can be compromised due to diagenetic effects, or (petrography-controlled) analytical artefacts. Such diagenetic or analytical artefacts typically have a detrimental impact on the accuracy of isotope equilibrium-based cave temperatures calculated from paired oxygen isotope values of FI water and host calcite.

Here, we will highlight some recent FI isotope records, discuss current views on the recognition of FI isotopic artefacts, and provide guidelines for the interpretation of FI isotope data as a paleo-rainfall proxy, with particular focus on direct comparison to novel TEX₈₆ paleotemperatures that can be derived from the same speleothem calcite.

How to cite: Vonhof, H., Markowska, M., Levy, E., Martinez Garcia, A., Nicholson, S., and Schroeder, J.: Retrieving the rainfall signature from the isotope composition of speleothem fluid inclusion water: progress and pitfalls, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9130, https://doi.org/10.5194/egusphere-egu23-9130, 2023.

09:25–09:35

EGU23-2303

ECS

On-site presentation

Tracking methane fluxes using intact polar and core lipids in an aridity transect of the Okavango Delta (Botswana)

Julie Lattaud, Mangaliso Gondwe, Darci Rush, Ellen Hopmans, Carole Helfter, and Cindy De Jonge

Wetland methane (CH₄) emissions are the largest natural source in the global CH₄ budget, contributing to roughly one third of total natural and anthropogenic emissions. As the second most important anthropogenic greenhouse gas in the atmosphere after CO₂, CH₄ is strongly associated with climate feedbacks. The different pathways of biochemical cycling of CH₄, which exert a primary control on atmospheric CH₄ concentrations through its production and biological consumption, remain poorly constrained. It is therefore crucial to understand and, if possible, quantify these variable CH₄sources to natural climate variability.

We studied a soil transect (up to seven sites, 250 m long) across a seasonal floodplain at Nxaraga on the south-west part of the Chief’s Island, Okavango Delta, Botswana, over three years (2018 – 2020, 50 samples in total). Previous studies showed a clear link between CH4 fluxes and soil water content in the area, with CH₄ fluxes in the seasonally flooded soils of up to 492 nmol m^-2 s^-1.

To constrain biomass active in CH₄production (specifically, methanogenic archaea) intact and core isoprenoid lipids (and their stable carbon isotope signature) were quantified on a High Performance Liquid Chromatograph (HPLC) and on an high-resolution mass spectrometer ("Orbitrap"). To constrain biomass of CH₄oxidizers (i.e. bacterial methanotrophs), core (hopanol) and intact lipids (i.e., bacteriohopanepolyols (BHPs)) were analyzed non-derivatized on an Orbitrap. Confirming their proposed methanotroph source, BHP-aminopentol and methylcarbamate-BHP were detected and their variation correlated positively with those of hopanols and archaeol lipids. Methyl-amino BHPs however were not detected in the soils. In-depth study of their environmental variation points towards two bacterial communities depending on the pH, EC and water content of the soils. This will be confirmed or refuted by bacterial community profiling based on 16S RNA genes, and functional genes for methane oxidation

How to cite: Lattaud, J., Gondwe, M., Rush, D., Hopmans, E., Helfter, C., and De Jonge, C.: Tracking methane fluxes using intact polar and core lipids in an aridity transect of the Okavango Delta (Botswana), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2303, https://doi.org/10.5194/egusphere-egu23-2303, 2023.

09:35–09:45

EGU23-9780

ECS

On-site presentation

Quantifying Holocene temperature changes using bacterial and archaeal membrane lipids (GDGTs) in the Swiss Alps

Fatemeh Ajallooeian, Sarah Nemiah Ladd, Nathalie Dubois, Carsten Schubert, Mark Alexander Lever, and Cindy De Jonge

Currently, Holocene paleoclimate research shows discrepancies in the timing and extent of the so-called Holocene “climate optimum” (1). To better understand this phenomenon in the alpine region, we examine the mean annual air temperature (MAT) record based on the distribution of Glycerol Dialkyl Glycerol Tetraethers (GDGTs) in a 14-m long sediment core from Lake Rot, Switzerland. This small eutrophic monomictic lake is characterized by a seasonally anoxic hypolimnion. An age model based on 20 calibrated ¹⁴C dates shows that the top 10 m of sediments reflect the early, middle, and late Holocene (10 cal. ka BP to recent).

To constrain environmental changes, we also look at total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN), and bulk organic matter δ¹³C and δ¹⁵N (n = 300). These indices give insight into the sources of organic matter in Lake Rot sediments. A stable and dominantly in-situ produced lacustrine source of organic matter is indicated by the range in C/N values (4-17) and d¹⁵N values (-0.37-5.84). Increasing TOC and δ¹³C values during the early Holocene (around 10 cal. ka BP), likely reflect elevated primary production in the lake during postglacial climate warming. Subsequently, high TIC values indicate a period with high calcite precipitation (10-8 cal. ka BP). Between 8-1.5 cal. ka BP, high TOC and very low TIC values indicate a dramatic change in the system, reflecting a higher production and/or conservation of organic matter. After this period, TOC decreases, showing a last increase in the top 50cm of the core, presenting signs of eutrophication. Lake Rot thus has experienced large changes in the last 10ka.

From a subset of 63 samples, GDGTs are analysed to reconstruct MAT using the methylation index of brGDGTs (MBT’_5ME). Using a lake calibration (2), reconstructed average MAT is 8.4℃ (RMSE = 2.1℃). The absence of large temperature changes during the Holocene highlights that the MBT’5ME-based reconstructed temperatures are not influenced by the large changes in water chemistry recorded by the bulk TOC and TIC values. Instead, the temperature reconstruction reflects stable Holocene temperature ranges, presenting no expressed “climate optimum” in this core. The most recent reconstructed temperature of 9.7℃ resembles actual measured MAT (10.7℃).

Based on our results, the isoprenoid GDGT TEX86 is not applicable for the reconstruction of temperature in Lake Rot. This matches a recent study of perialpine lakes where the successful application of TEX₈₆ was suggested to be limited to deep lakes (>100 m) (3). In addition, we will discuss whether production of in-situ brGDGTs in the water column and seasonality influence the sediment temperature record, as proposed by the authors and other studies (2,4).

1: Herzschuh et al., (2022). EGUsphere, 1-23.

2: Russell et al., (2018). Organic Geochemistry, 117, 56-69.

3: Damsté et al., (2022). Quaternary Science Reviews, 277, 107352.

4: Loomis et al., (2014). Geochimica et Cosmochimica Acta, 144, 173-187.

How to cite: Ajallooeian, F., Ladd, S. N., Dubois, N., Schubert, C., Lever, M. A., and De Jonge, C.: Quantifying Holocene temperature changes using bacterial and archaeal membrane lipids (GDGTs) in the Swiss Alps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9780, https://doi.org/10.5194/egusphere-egu23-9780, 2023.

09:45–09:55

EGU23-188

ECS

On-site presentation

Long-term changes in Carbon accumulation in mountain peatbogs in the South-West of Norway

Christian Quintana, Anne Bjune, Alistair Seddon, and Hanna Lee

There is relevant research on temporal carbon accumulation changes, mostly in arctic permafrost peatlands in Norway, but little is known about the differences and comparisons with more oceanic and lower latitude peatlands in the region, where rainfall is one of the main climatic drivers. Climate projections in Norway for 2031-2060 and 2071-2100 show a rise in mean temperature and an increase of annual rainfall with more intense seasonal events in western, eastern, and northern parts. Under this rationale, this study hypothesizes that temporal variability of temperature and precipitation during the Holocene led to weaker and stronger evapotranspiration and moisture signals affecting local and regional vegetation in peatland ecosystems, water-table changes, and carbon accumulation capacity. This study will contribute to the generation of evidence of the roles and interactions of hydrology, temperature, vegetation, and land use changes on peatbogs carbon accumulation capacity during the Holocene. It will help to disentangle the responses of the carbon budget at different time scales. Methods involve the use of a set of proxies such as pollen, testate amoeba, LOI and bulk density to reconstruct the peat composition rate, organic matter, water table, and local (and regional) vegetation. A generation of an age-depth model and further multivariate analysis will allow to investigate the relationship between the proxies and carbon accumulation rate over the Holocene to further understand the temperature/precipitation correlation and the effects of a changing climate on the carbon budget.

How to cite: Quintana, C., Bjune, A., Seddon, A., and Lee, H.: Long-term changes in Carbon accumulation in mountain peatbogs in the South-West of Norway, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-188, https://doi.org/10.5194/egusphere-egu23-188, 2023.

09:55–10:05

EGU23-6593

ECS

On-site presentation

Applying Brillouin thermometry as a novel tool for reconstructing temperatures, depths, and seasonal biases of Holocene/Pleistocene Searles Lake, California

Kristian Olson, Emmanuel Guillerm, Mark Peaple, Tim Lowenstein, Véronique Gardien, Frédéric Caupin, Sarah Feakins, Jessica Tierney, Justin Stroup, Steve Lund, and David McGee

Paleoclimate records from lakes of the southwestern USA have been limited by a lack of independent paleothermometers, resulting in conflicting characterizations of millennial-scale variability in temperature and moisture. Here a novel method called Brillouin thermometry is applied to halite-bearing dry intervals of the late Pleistocene/Holocene (45–0 ka) core record of Searles Lake, California. Halite from the sediment-water interface records lake bottom temperatures during dry, high salinity periods. Analysis of modern saline lakes of various chemistries, depths, climate zones, and mixing regimes shows that: 1) average bottom water temperature is approximately equal to mean annual air temperature, and 2) annual range of bottom water temperature is inversely proportional to lake depth. Brillouin temperatures for eight halite intervals 30.6 ka to 8.5 ka range from 11.8 ± 3.6 to 22.4 ± 3.2 °C. Bottom water temperature variability indicates paleolake depths of ~10 m during halite precipitation. Brillouin thermometric results are then assessed in comparison with two additional temperature proxy records from the same Searles Lake sediment core: 1) branched glycerol dialkyl glycerol tetraethers (brGDGTs) extracted from wet mud intervals, and 2) thermodynamic constraints from evaporite minerals and mineral sequences. Temperatures from brGDGTs for mud intervals 44.7 ka to 3.6 ka range from 13.4 ± 2.8 to 23.9 ± 3.0 °C. Comparisons of Brillouin/brGDGT temperatures with predicted equilibrium temperatures of salt crystallization indicate intervals where seasonal temperature variability forced the dissolution and/or recrystallization of existing temperature-sensitive evaporites. The multiproxy temperature record of Searles Lake agrees with other regional records at glacial/interglacial timescales but displays a wider degree of millennial-scale variability, with temperatures during the last glacial ranging from 8.3 °C below modern mean annual temperatures to 3.8 °C above.

How to cite: Olson, K., Guillerm, E., Peaple, M., Lowenstein, T., Gardien, V., Caupin, F., Feakins, S., Tierney, J., Stroup, J., Lund, S., and McGee, D.: Applying Brillouin thermometry as a novel tool for reconstructing temperatures, depths, and seasonal biases of Holocene/Pleistocene Searles Lake, California, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6593, https://doi.org/10.5194/egusphere-egu23-6593, 2023.

Posters on site: Tue, 25 Apr, 16:15–18:00 | Hall X5

Chairpersons: Cindy De Jonge, Bethany Fox, Sebastian F.M. Breitenbach

X5.156

EGU23-1460

ECS

Warmer and wetter past interglacials in northeast Greenland recorded in speleothems

Anika Donner, Gina E. Moseley, Werner Kofler, Laurent Marquer, Lena Friedrich, Christoph Spötl, and R. Lawrence Edwards

The Arctic is particularly sensitive to climate warming and the impacts of this warming are expected to have global consequences. In order to improve understanding of the Arctic’s amplified response, it is valuable to study past interglacial periods. In contrast to existing palaeoclimate records for some areas in the Arctic, Greenland prior to 130 ka remains under-investigated. Northeast Greenland, especially, is one of the regions where the effects of Arctic amplification are particularly pronounced, both within the observational period as well as modelled future scenarios. In this study, we utilise inactive speleothems from caves in northeast Greenland (80°N) to investigate the palaeoenvironment of the region. In today’s environment, speleothem deposition is prevented by an arid climate (ca. 200 mm a^-1) and frozen ground. Accordingly, the presence of extensive speleothem deposits in the region suggests that there was at least one period of wetter and warmer climate in the recent geological past. The most recent significant speleothem deposition occurred during marine isotope stage 11 (MIS11). Prior to this, the extended MIS13-15 interglacial period was a period of exceptionally prolific speleothem deposition in northeast Greenland. During these two growth phases, the δ¹⁸O and δ¹³C variability show large centennial-scale excursions. Preliminary investigations into pollen preserved in MIS11 speleothem samples suggest an environment vastly different to today, where the landscape is mostly barren except for a few small alpine plants and shrubs. For MIS11, the samples indicate the presence of boreal coniferous species such as Picea, Abies and Pinus as well as others such as Corylus, Alnus, Ericaceae, Cyperaceae, and Poaceae. These results are in agreement with a record of MIS11 vegetation in a marine core off the coast of south Greenland, and while still being under investigation, this could imply that the reconstructed forestation of south Greenland during MIS11 reached further north. Preserved floral macrofossils and large amounts of spores in the speleothem samples indicate potential for further investigations of environmental conditions in northeast Greenland during a warmer and wetter past.

How to cite: Donner, A., Moseley, G. E., Kofler, W., Marquer, L., Friedrich, L., Spötl, C., and Edwards, R. L.: Warmer and wetter past interglacials in northeast Greenland recorded in speleothems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1460, https://doi.org/10.5194/egusphere-egu23-1460, 2023.

X5.157

EGU23-1735

ECS

Polycyclic Aromatic Hydrocarbons (PAHs) in speleothems.

Julia Homann, Sebastian Breitenbach, Stacy Carolin, David Hodell, Jessica Oster, Cameron de Wet, and Thorsten Hoffmann

Secondary mineral deposits in caves, such as stalagmites, constitute valuable paleoclimate archives because they are largely protected from degradation by stable in-cave conditions and can be precisely dated In addition to established climate proxies such as stable isotopes and trace elements, organic proxies have become increasingly attractive in recent years for the study of paleo vegetation, wildfires, and hydrodynamics. [1]

Biomass burning events are major sources of atmospheric particulate matter that influences global and local climate. [2] Investigating fire proxies in paleoclimate archives may therefore help determine the interactions of climate, hydrology, and fire activity.

Polycyclic Aromatic Hydrocarbons (PAHs) are organic molecules made up of two or more fused aromatic rings. They stem from the incomplete combustion of organic matter. Their persistence in the environment makes them useful for the reconstruction of fire events from paleoenvironmental archives like sediments, peat, ice cores, and soils. [3-6] Their presence has also been reported in speleothems, however, only a limited range of PAHs seem to be transported into the cave and subsequently preserved in speleothem carbonate. [7, 8]

We present a new sample preparation method for the extraction of PAHs from speleothem and the subsequent extraction of levoglucosan, an anhydrosugar derived from the combustion of cellulose that also constitutes a marker for biomass burning. We apply this method to speleothems from Cenote Ch'en Mul, Mayapan, on the Yucátan peninsula, and White Moon Cave, California, to investigate the relationship between PAHs and levoglucosan. Such tandem approach will deepen our understanding of paleo-fire dynamics and strengthen proxy-based reconstructions.

[1] A. Blyth et al. Quat. Sci. Rev. 149 (2016) 1-17 [2] P. Yao et al. J. of Glaciology 59 (2013) 599-611 [3] Tan et al. Palaeogeography, Palaeoclimatology, Palaeoecology 560 (2020) 110015 [4] Argiriadis et al. Microchem. J. 156 (2020) 104821 [5] Vecchiato et al. Sci. Rep. (2020) 10:10661 [6] Chen et al. ACS Earth Space Chem. 2018, 2, 1262−1270 [7] Argiriadis et al. Anal. Chem. 2019, 91, 7007−7011 [8] Perrette et al. Chem. Geol. 251 (2008) 67–76

How to cite: Homann, J., Breitenbach, S., Carolin, S., Hodell, D., Oster, J., de Wet, C., and Hoffmann, T.: Polycyclic Aromatic Hydrocarbons (PAHs) in speleothems., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1735, https://doi.org/10.5194/egusphere-egu23-1735, 2023.

X5.158

EGU23-2706

crestr: An R package to perform probabilistic climate reconstructions from palaeoecological datasets

Manuel Chevalier and Brian M. Chase

Quantitative climate reconstructions are fundamental to better understanding past environmental changes and evaluating climate simulations. The proliferation of pollen-based reconstructions during the past decades has been instrumental in improving our understanding of past climate dynamics across various spatial and temporal scales. However, this knowledge has been mainly concentrated in North America and parts of Eurasia, and very few quantifications exist in the tropics. This global data imbalance is partly due to the sparser network of supporting pollen records in these regions and, in equal proportions, to the limitations of the most commonly used reconstruction techniques (e.g. the analogue technique or WA-PLS) in dealing with the specificities of tropical vegetation. To address this problem and produce the much-needed climate quantification from tropical regions, we propose using the probabilistic method CREST (Climate REconstruction SofTware) that uses probability density functions (‘pdfs’) fitted on modern occurrence plant data to reconstruct environmental parameters. CREST, which has been successfully employed in Africa and South America, offers many advantages over the classical approaches, including 1) a higher flexibility of application, 2) a better capacity to estimate uncertainties, and thanks to the recent developments of a dedicated R package crestr that includes a global calibration dataset, 3) CREST is applicable in every environment where plants currently grow. Considering these advantages, the large-scale application of CREST to quantitatively reconstruct important climate parameters from the existing tropical fossil pollen records should 1) help better integrate and interpret regional proxy compilations, 2) shed light on the spatiotemporal climate variability of tropical regions, and 3) determine the main modes of tropical climate variability. With this contribution, we will showcase the use of the crestr package with a novel temperature reconstruction derived from the 270,000-year-long, high-resolution pollen record from Laguna Fùquene in Colombia and discuss how this type of analysis could be generalised to determine spatial patterns of climate change from multi-record reconstructions

How to cite: Chevalier, M. and Chase, B. M.: crestr: An R package to perform probabilistic climate reconstructions from palaeoecological datasets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2706, https://doi.org/10.5194/egusphere-egu23-2706, 2023.

X5.159

EGU23-3736

ECS

The Influence of Temperature on the Fall of the Guge Kingdom in Western Tibet, China

Haichao Xie and Jie Liang

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) from lacustrine sediments have been widely used to reconstruct mean annual air temperature (MAAT). Although many proxy calibrations relating brGDGT characteristics have been put forth, these calibrations may produce warm biases when applied to lakes in cold regions. We present an expanded Chinese lake surface sediment brGDGT-MAAT calibration with 29 new surface samples from cold regions along with 39 previously published from Chinese lakes. We deployed sediment traps in a meromictic lake, Dagze Co, and compared results with previously published data from a dimictic lake, Lake 578 in Greenland, to determine potential seasonal and depth-dependence of brGDGTs. In the meromictic lake, brGDGTs are primarily produced in the lake bottom water, whereas in the dimictic lake, the brGDGTs are produced throughout the water column and mainly reflect the annual bottom water temperature or mixing season water column temperature. We applied our refined calibration to a sediment core from Western Tibet to examine how fluctuations in temperature influenced the Guge Kingdom over the last 2,000 years. Our record reveals relatively warm temperatures during the Medieval Climate Anomaly, cooling of 2°C to -2°C during the Little Ice Age, warming into the eighteenth century, and stabilization after 1800 CE. The temperature variations coincided with a transition of dynasties in Western Tibet. Temperature sensitivity tests on barley distribution, the principal cultivated cereal in Tibet, suggest that a decline in temperature led to a decreased crop yield that may have factored into the disappearance of the Guge Kingdom.

How to cite: Xie, H. and Liang, J.: The Influence of Temperature on the Fall of the Guge Kingdom in Western Tibet, China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3736, https://doi.org/10.5194/egusphere-egu23-3736, 2023.

X5.160

EGU23-8094

Dansgaard-Oeschger climate oscillation during the early MIS3 in Europe: evidence from a multi proxy (bulk & clumped stable isotopes and trace elements) speleothem record in Han-sur-Lesse, Belgium

Marion Peral, Marta Marchegiano, Sophie Verheyden, Steven Goderis, Tom Van Helden, Frank Vanhaecke, Thibaut Van Acker, Jia Xuexue, Hai Cheng, and Philippe Claeys

The Marine Isotope Stage 3 (MIS 3) – a period between 60 and 27 ka ago during the last glacial cycle – experienced several abrupt climatic warming phases known as Dansgaard-Oeschger (DO) events. The DO events are abrupt transitions from cold (stadial) to mild (interstadial) climate conditions.

Speleothems are precious continental records and provide important climatic information at high resolution. However, during this time period, the north central Europe is less studied because the MIS 3 is generally not recorded, due to the climatic conditions. Here, we present the first Belgium continuous speleothem (flowstone) record covering the early MIS 3 (from 60 to 40 ka) from the Verviétois Gallery that is part of the Han sur Lesse cave system (southern Belgium). High resolution bulk stable isotope and elemental combined with U-Th dating are used to define the Belgium climatic variability. Additionally, clumped isotope measurements have been performed to reconstruct temperature to better constrain climatic response during the DO 16-12.

The multiproxy approach used to investigate the speleothem record shows a regional response to the global climate conditions during MIS3. The d¹³C and d¹⁸O values as well as the elemental analyses (Mg, Ba and Sr as water availability proxies and P and Zn as soil development) mirror the DO 16 and 12 events indicating dry-wet and cold-warm changes. During interstadials events low values of d¹⁸O and d¹³C and Mg, Ba and Sr content suggest wet/warm conditions, while the increase of isotopic and elemental values during the stadials support a climate deterioration with cooling and drier conditions. The clumped-isotope temperatures, performed on the DO 16 and 12, suggest warm interstadials (12^OC +/- 2^OC) and cold stadials (7^OC +/- 2^OC) climate.

During the DO12, a delay in the climatic amelioration and the vegetation is observed. This delay, also noted in south-west France cave (Villars cave), seems to be linked to a delay between increase of temperature and water availability allowing the soil above the cave to growth. Also, a climatic deterioration occurred after the DO11, with an increase time lag from the north to the south of Europe, showing a progressive cooling to the south Europe. It is interesting to note that this gradual cooling in Europe coincides, withing dating error bars, with the potential progressive north-south decline of the Neanderthals in Europe.

How to cite: Peral, M., Marchegiano, M., Verheyden, S., Goderis, S., Van Helden, T., Vanhaecke, F., Van Acker, T., Xuexue, J., Cheng, H., and Claeys, P.: Dansgaard-Oeschger climate oscillation during the early MIS3 in Europe: evidence from a multi proxy (bulk & clumped stable isotopes and trace elements) speleothem record in Han-sur-Lesse, Belgium, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8094, https://doi.org/10.5194/egusphere-egu23-8094, 2023.

X5.161

EGU23-9362

Resurrecting lost forests – speleothems inform on environmental changes in northern Scotland during MIS 5e

Sebastian F.M. Breitenbach, Julia Homann, Hamish Couper, Beth R.S. Fox, Ola Kwiecien, Tim J. Lawson, Thorsten Hoffmann, Gideon M. Henderson, and Tim C. Atkinson

Modern Northern Scotland is a largely barren landscape, with most of the natural temperate rainforest that covered the Atlantic side of Great Britain lost to active deforestation and overgrazing, mainly by sheep and deer (Shrubsole 2022). Pockets of relic temperate rainforest are reminders of the significant changes induced by the arrival of humans and their domestic animals. However, little is known about early Holocene and previous interglacial environmental conditions, and here we propose an unorthodox archive of natural vegetation cover of Scotland.

We present a new U-Th dated speleothem from the previous interglacial (MIS 5e/Ipswichian) and use stable oxygen and carbon isotope ratios, in tandem with lignin, a biopolymer with three monomers, to gain insight into last interglacial environmental conditions in Assynt, NW Scotland. The lignin monomer ratio provides information about relative changes between gymnosperm vs. angiosperm plant communities, and thus on changes in vegetation (e.g., from pine forest to moorland or grassland).

Flowstone TJL20080901 was found broken and recovered in 2008 from Rana Hole, a cave at 352 m above sea level overlain by heather moorland overlying blanket peat (Lawson & Dowswell 2022). Seven U-Th dates, analysed at Oxford University, show that this calcite flowstone was deposited between 127 and 119 ka BP during Marine Isotope Stage 5e, with an average growth rate between 20 and 40 μm/yr.

We suggest that speleothem δ¹³C indicates local infiltration and vegetation and soil composition, whereas δ¹⁸O reflects the history (source, temperature, seasonality) of the moisture feeding the cave stream from which the flowstone was precipitated. The lignin composition directly relates to local vegetation cover.

Our new multi-proxy record provides unique insights into environmental conditions in Assynt during MIS 5e, and the history of vegetation developing without human interference.

References

Homann et al. (2022) Linked fire activity and climate whiplash in California during the early Holocene. Nature Communications 13:7175

Lawson T. J. & Dowswell P. N. F. (2022) Caves of Assynt (3^rd edition). Grampian Speleological Group. Edinburgh, 211 pages, ISBN 987-1-7397635-0-3

Shrubsole G. (2022) The lost rainforests of Britain. HarperCollins Publishers, 336 pages, ISBN 9780008527952

How to cite: Breitenbach, S. F. M., Homann, J., Couper, H., Fox, B. R. S., Kwiecien, O., Lawson, T. J., Hoffmann, T., Henderson, G. M., and Atkinson, T. C.: Resurrecting lost forests – speleothems inform on environmental changes in northern Scotland during MIS 5e, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9362, https://doi.org/10.5194/egusphere-egu23-9362, 2023.

X5.162

EGU23-9507

Timescales of volcanic impacts on terrestrial and aquatic ecosystems in the Eastern Mediterranean

Nadine Pickarski, Ola Kwiecien, and Thomas Litt

Instrumental data show that while the impact of volcanic eruptions on their immediate vicinity is destructive, long-term consequences can be beneficial. However, beyond last millennia observational data and ancient oral history, the detailed insights into timescales and scopes of recovery remain largely unresolved. Here we illustrate the complex response of local and regional vegetation, aquatic ecosystem, and fire activity to volcanic eruptions in close connection to prevailing climate conditions and assess the recovery time in varve-years.

We selected five volcaniclastic layers in the annually laminated sediments from Lake Van (Turkey). Analysed intervals cover glacial, interglacial, stadial and interstadial snapshots (spanning from Marine Isotope Stages 3 to 9e) and facilitate studying ecosystem’s responses under different climatic boundary conditions. Using high-resolution pollen data, non-pollen palynomorphs, and microscopic charcoal particles (>20 µm) we attempted to disentangle climatic and volcanic forcing of natural environmental disturbances. Our results highlight that the thickness of subsequent volcanic deposits and the respective climatic conditions strongly influence the impact on terrestrial and aquatic ecosystems. Similarily, the vegetation types predominant before the volcanic eruption have a decisive influence on subsequent pollen productivity and vegetation composition. On land, the most common response to ash deposition is a sudden shift towards steppe herbaceous taxa and abrupt fire activity. The affected herbaceous vegetation can recover to pre-eruption levels in as few as 20 to 40 varve-years. On the contrary, the lake water experiences intensified productivity due to subsequent nutrient input and significant short-term increase in aquatic taxa and non-siliceous microfossils.

Our approach helps in understanding complex ecosystems subjected to a variety of influencing factors operating on different time scales. Our results show the importance of distinguishing between the impact of tephra deposition and volcanically-induced climate change for tracking short-term ecosystem changes superimposed on long-term trends.

How to cite: Pickarski, N., Kwiecien, O., and Litt, T.: Timescales of volcanic impacts on terrestrial and aquatic ecosystems in the Eastern Mediterranean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9507, https://doi.org/10.5194/egusphere-egu23-9507, 2023.

X5.163

EGU23-13661

Development of new global lake brGDGT-temperature calibrations: advances, applications and challenges

Emma Pearson, Steve Juggins, Stephen Roberts, Tony Phillips, Dominic Hodgson, David Naafs, Louise Foster, and Harry Allbrook

Quantitative paleoclimate reconstructions are fundamental to understand long-term trends in natural climate variability and to test climate models used to predict future climate change. Branched glycerol dialkyl glycerol tetrathers (brGDGTs) are bacterial cell membrane lipids, with a molecular structure that strongly depends on growth temperature, and global and regional lacustrine brGDGT-temperature calibrations have been used to reconstruct past temperatures using lake sediments from a range of environments.

Application of the global and regional Antarctic and sub-Antarctic brGDGT calibrations (Pearson et al., 2011; Foster et al., 2016) however, suggests a need to expand and improve reconstruction accuracy for cold, extreme environments (Roberts et al., 2017). We construct new global lacustrine brGDGT-temperature calibrations using datasets obtained via brGDGT analysis using two existing (single and dual column LCMS) analytical methods, and comprising Antarctic and sub-Antarctic samples, and other available published datasets.

Advancements in calibration studies principally comprise two main routes: one via expansion of calibration datasets, the other by improving reconstructions. We address both of these by both expanding existing datasets, and also by evaluating a range of different statistical approaches, all of which are subjected to rigorous cross-validation. For each of our calibration datasets we investigate a range of different statistical modelling approaches to predict mean annual temperature, mean summer temperature and mean temperature of months above freezing, where available, derived from field measurements and the gridded ERA5 dataset (Hersbach et al., 2019) across the whole and <15°C subset of the temperature range.

We apply our new calibrations to existing published lake sediment core records from contrasting environments to compare and evaluate the performance of the different analytical and statistical methods. Our findings highlight some of the complexities and caveats of the different methods and have important implications for the application of lacustrine brGDGT temperature calibrations to lakes at a global scale.

References

Foster LC, Pearson EJ, Juggins S, Hodgson DA, Saunders KM, Verleyen E, Roberts SJ. Development of a regional glycerol dialkyl glycerol tetraether (GDGT)–temperature calibration for Antarctic and sub-Antarctic lakes. Earth and Planetary Science Letters 2016, 433, 370-379.

Hersbach, H., Bell, B., Berrisford, P., Biavati, G., Horányi, A., Muñoz Sabater, J., Nicolas, J., Peubey, C., Radu, R., Rozum, I., Schepers, D., Simmons, A., Soci, C., Dee, D., Thépaut, J-N. (2019): ERA5 monthly averaged data on single levels from 1979 to present. Copernicus Climate Change Service (C3S) Climate Data Store (CDS). (Accessed on 08-Sep-2020, 29-Mar-2021), 10.24381/cds.f17050d7

Pearson EJ, Juggins S, Talbot HM, Weckström J, Rosén P, Ryves D, Roberts S, Schmidt R. A lacustrine GDGT-temperature calibration from the Scandinavian Arctic to Antarctic: Renewed potential for the application of GDGT-paleothermometry in lakes. Geochimica et Cosmochimica Acta 2011, 75(20), 6225-6238.

Roberts SJ, Monien P, Foster LC, Loftfield J, Hocking EP, Schnetger B, Pearson EJ, Juggins S, Fretwell P, Ireland L, Ochyra R, Haworth AR, Allen CS, Moreton SG, Davies SJ, Brumsack H-J, Bentley MJ, Hodgson DA. Past penguin colony responses to explosive volcanism on the Antarctic Peninsula. Nature Communications 2017, 8, 14914.

How to cite: Pearson, E., Juggins, S., Roberts, S., Phillips, T., Hodgson, D., Naafs, D., Foster, L., and Allbrook, H.: Development of new global lake brGDGT-temperature calibrations: advances, applications and challenges, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13661, https://doi.org/10.5194/egusphere-egu23-13661, 2023.

X5.164

EGU23-14517

ECS

A Miocene (23–12.5 Ma) continental paleotemperature record from the northern Mediterranean region (Digne-Valensole Basin, SE France)

Armelle Ballian, Maud J. M. Meijers, Katharina Methner, Isabelle Cojan, Damien Huyghe, Jens Fiebig, and Andreas Mulch

During the Middle Miocene the Earth’s climate shifted from a warm phase, the Miocene Climatic Optimum (MCO, 16.9–14.7 Ma), to a colder phase associated with the formation of major and permanent Antarctic ice sheets. This climatic shift, the Middle Miocene Climatic Transition (MMCT, 14.7–13.8 Ma), had significant impact on the composition and structure of major biomes (e.g. Jimenez-Moreno & Suc, 2007) and impacted worldwide ocean circulation (Holbourn et al., 2014) as well as terrestrial temperature and precipitation patterns (e.g. Methner et al., 2020). While the MCO and the subsequent MMCT are well described in marine records, quantitative continental paleoclimate records are still lacking when it comes to constraining the magnitude and rate of terrestrial environmental change. Collectively, δ¹⁸O, δ¹³C and Δ₄₇ data from soil carbonates provide information about past environmental and climatic conditions, such as (seasonality of) precipitation, soil temperature as well as vegetation patterns. The formation of soil carbonates is mainly controlled by the interplay of environmental factors such as soil water composition, soil temperature, and soil CO₂. We compare the stable (δ¹⁸O, δ¹³C) and clumped (Δ₄₇) isotopic composition of pedogenic carbonate nodules of the Digne-Valensole Basin (SE France) with time equivalent counterparts from central Europe (Northern Alpine Molasse Basin, Switzerland) and present a ca. 23 – 12.5 Ma biostratigraphically-controlled clumped isotope paleotemperature record from the SW-foreland of the European Alps. Alluvial fan deposition and soil formation in the Digne-Valensole Basin occurred near sea level as documented by the intercalation of marine and continental facies (Cojan et al., 2013). Our Δ₄₇ results from the Digne-Valensole Basin indicate relatively warm and stable carbonate formation temperatures (ca. 32°C) for the Early Miocene (23–19.5 Ma) followed by enhanced temperature fluctuations attaining maximum values at the onset of the MCO. The Digne-Valensole temperature pattern correlates with age-equivalent Δ₄₇temperatures from the Northern Alpine Foreland Basin. In both records, significant climatic changes can be observed at the onset of the MCO and the MMCT, which are documented by major rapid shifts in paleotemperatures (ca. 15°C within 300 ka). However, the proximity to the Mediterranean Basin is clearly visible in the Digne-Valensole records as expressed in rather high δ¹⁸O values of meteoric water that average ca. −3.5 ‰. Combining our data with the Northern Alpine foreland records results in a coherent climate pattern for the Alpine foreland during the Middle Miocene.

Cojan et al. (2013) https://doi.org/10.2113/gssgfbull.184.6.583

Holbourn et al. (2014) https://doi.org/10.1130/G34890.1

Jimenez-Moreno & Suc (2007) https://doi.org/10.1016/j.palaeo.2007.03.040

Methner et al. (2020) https://doi.org/10.1038/s41598-020-64743-5

How to cite: Ballian, A., Meijers, M. J. M., Methner, K., Cojan, I., Huyghe, D., Fiebig, J., and Mulch, A.: A Miocene (23–12.5 Ma) continental paleotemperature record from the northern Mediterranean region (Digne-Valensole Basin, SE France), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14517, https://doi.org/10.5194/egusphere-egu23-14517, 2023.

X5.165

EGU23-16852

ECS

A comparative study of cave system Ca isotope ratios with rainfall, δ13C, and trace element data: Implications for quantitative reconstructions of paleorainfall from speleothems

Cameron de Wet, Elizabeth Griffith, Andrea Erhardt, Harold Bradbury, Alexandra Turchyn, and Jessica Oster

The development of quantitative records of past rainfall is an outstanding goal in the field of speleothem paleoclimatology and represents an essential step for benchmarking paleoclimate model simulations. However, most traditionally-employed speleothem proxies, including δ¹⁸O, δ¹³C, and trace-element-to-calcium ratios, respond to a number of complex climatic and environmental influences and typically provide only qualitative records of paleoclimate change. Variations in speleothem Ca isotope ratios (δ⁴⁴Ca) are thought to be uniquely controlled by carbonate mineral precipitation above a drip site (prior carbonate precipitation, or PCP), which can be modeled as a Rayleigh fractionation process and calibrated with modern rainfall data. Thus, speleothem δ⁴⁴Ca shows promise as a semi-quantitative proxy for past changes in local effective rainfall rates. However, few cave monitoring studies have focused specifically on the ways in which important factors, like host rock δ⁴⁴Ca variability and geology, water flow path geometry, ventilation, and seasonal rainfall distribution affect δ⁴⁴Ca signals in speleothems.

We present a comparative study of δ⁴⁴Ca data and coeval measurements of δ¹³C and trace element ratios, established proxies for water infiltration, from cave drip waters, farmed calcite, and host rocks from three different cave systems in the United States- White Moon Cave (WMC) in coastal California, Lake Shasta Caverns (LSC) in northern California, and Blue Springs Cave (BSC) in east-central Tennessee. These cave systems are characterized by different hydroclimate, geology, flow path geometry, and seasonal infiltration characteristics.

To assess the relationship between Ca isotope variability and effective rainfall, we use Rayleigh fractionation equations to estimate the amount of PCP occurring at each cave site and compare these estimates with local rainfall rates, supplementing with drip rate information when possible.

The comparison of WMC, LSC, and BSC δ⁴⁴Ca, δ¹³C, and trace element data from drip sites with different flow path geometry and from caves in different geologic and climate settings allows for these key factors to be assessed independently. This work, and the direct comparison between δ⁴⁴Ca measurements and measured local rainfall rates in particular, aids in the refinement of speleothem δ⁴⁴Ca as a new, semi-quantitative proxy for paleorainfall.

How to cite: de Wet, C., Griffith, E., Erhardt, A., Bradbury, H., Turchyn, A., and Oster, J.: A comparative study of cave system Ca isotope ratios with rainfall, δ13C, and trace element data: Implications for quantitative reconstructions of paleorainfall from speleothems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16852, https://doi.org/10.5194/egusphere-egu23-16852, 2023.

X5.166

EGU23-16916

ECS

High-resolution reconstruction of the hydroclimate and palaeoenvironment of the last 5500 years in the Apuseni Mountains (NW Romania)

Agnes Ruskal, Andrei-Cosmin Diaconu, Andrei Panait, Mariusz Gałka, Angelica Feurdean, and Ioan Tanțău

In the present study, we analyzed an ombrotrophic peat sequence from NW Romania using a multi-proxy approach (lithology, radiocarbon dating, loss on ignition, magnetic susceptibility, testate amoebae and plant macrofossil) in order to reconstruct the environmental and hydroclimate changes that occurred in the last 5500 years.

The studied sequence (Molhașul Mare de la Izbuc, Apuseni Mountains) started to accumulate in 5520 cal yr BP, debutting with a lacustrine phase and evolving into an ombrotrophic Sphagnum peat bog. The palaeoenvironmental stages of the peat bog were confirmed by the lithology, loss on ignition and magnetic susceptibility results. A pan-european testate amoebae-based transfer function was used for the quantitative reconstruction of the water table levels in the peatland. The depth to water-table (DWT) values ranged between 7.3 and 28.5 cm, suggesting wetter conditions in the first 2500 years of the sequence and drier ones between 2500 cal yr BP and the present days. The occurred hydrological shifts and the changes of the surface wetness were also confirmed by the plant macrofossil analyses.

We identified and assessed the local effects of several rapid climate change events that occurred in Europe such as the Piora Oscillation, Middle Bronze Age Cold Event, Iron Age Cold Event, Roman Climate Optimum, Dark Age Cold Event, Medieval Warm Period, Little Ice Age, Great Famine in Europe, the Sporer, Maunder and Dalton Minimum Events and the Year Without Summer.

Our high resolution study is among the few quantitative DWT reconstructions in Romania. Our results contribute to obtaining a broader image and a better understanding of the palaeoenvironmental, palaohydrological and palaeoclimate changes in Romania and in Central Eastern Europe during the past 5500 years.

How to cite: Ruskal, A., Diaconu, A.-C., Panait, A., Gałka, M., Feurdean, A., and Tanțău, I.: High-resolution reconstruction of the hydroclimate and palaeoenvironment of the last 5500 years in the Apuseni Mountains (NW Romania), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16916, https://doi.org/10.5194/egusphere-egu23-16916, 2023.

X5.167

EGU23-8090

ECS

A Late Holocene δ18O paleoclimate record from the afro-alpine Lake Garba Guracha, Bale Mountains Ethiopia: implications for human occupation/abandonment

Samuel, Getachew Chernet, Lucas Bittner, Graciela Gil-Romera, and Michael Zech

The Late Holocene, being a period when human footprint in paleoenvironmental archives became increasingly apparent, records important information about how early humans adapted to ever changing climatic conditions. Garba Guracha is an afro-alpine cirque lake located in the Bale Mountains National Park in the southeastern highlands of Ethiopia. The reconstructed age depth model with a time resolution of 10 years/cm makes it one of the best climate archives in the highlands of Eastern Africa. A total of 15.5 meter core recording 16 ka of sedimentation was retrieved from the lake. Previous works done on the archive include: (i) establishing the age-depth model and determination of sedimentation rates using bulk sedimentary organic matter, bulk n-alkane and charcoal ¹⁴C ages (Bittner et al. 2020); (ii) multi-proxy paleoenvironment reconstruction using charcoal, diatoms, biomarkers, and stable isotopes (Bittner et al., 2022; Gil-Romera et al., 2019). Results from these works show a strong variability for the late Holocene that represents the termination of the African Humid Period (AHP) and increased fire intensity. This study focuses on the topmost sedimentary succession of the core representing the late Holocene (~5 ka to present) and implements δ¹⁸O_sugar extracted from organic matter derived sugar biomarkers in high resolution (every 4 cm). The δ¹⁸O_sugarrecord can be used for reconstructing the lake evaporation history. Furthermore, combing these new data with other data obtained from n-alkane, charcoal and archaeological studies will shade light on a possible climate human interactions in high alpine ecosystem.

References

Bittner, L., Bliedtner, M., Grady, D., Gil-Romera, G., Martin-Jones, C., Lemma, B., Mekonnen, B., et al., 2020. Revisiting afro-alpine Lake Garba Guracha in the Bale Mountains of Ethiopia: rationale, chronology, geochemistry, and paleoenvironmental implications. Journal of Paleolimnology 64, 293–314.

Bittner, L., Gil-Romera, G., Grady, D., Lamb, H., Lorenz, E., Weiner, M., Zech, M. (2022). The Holocene lake-evaporation history of the afro-alpine Lake Garba Guracha in the Bale Mountains, Ethiopia, based on δ¹⁸O records of sugar biomarker and diatoms. Quaternary Research, 105, 23-36.

Gil-Romera, G., Adolf, C., Benito Blas, M., Bittner, L., Johansson, M.M.U., Grady, D.D.A., Lamb, H.H.F., et al., 2019. Long-term fire resilience of the Ericaceous Belt, Bale Mountains, Ethiopia. Biology Letters 15, 20190357.

How to cite: Chernet, S. G., Bittner, L., Gil-Romera, G., and Zech, M.: A Late Holocene δ18O paleoclimate record from the afro-alpine Lake Garba Guracha, Bale Mountains Ethiopia: implications for human occupation/abandonment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8090, https://doi.org/10.5194/egusphere-egu23-8090, 2023.

Posters virtual: Tue, 25 Apr, 16:15–18:00 | vHall CL

Chairperson: Jessica Oster

vCL.1

EGU23-15079

ECS

Peat core sequence in the Northern Carpathians, Romania. Fire and mining activities relationship over the late Holocene

Anca Petras

We aimed to understand relationship between fire and mining activities over the late Holocene, to predict modifications in study area are conditioned by climate change, and ongoing global warming could lead to wildfire changes or mining can cause change in landscapes, in region especially peatlands at mid-altitude. The reconstruction of long-term (thousands of years) wildfire regime and activity is possible by analyzing the abundance of carbonaceous vegetation fragments (charcoal) preserved in sediments accumulated in different depositional environments (e.g., peatlands). Charcoal is proxy used for reconstructing regional changes in wildfire regime and anthropogenic activity such as mining history, local soil and bedrock erosion was also reconstructed using a multi-proxy method: geochemistry, magnetic mineral properties and particle size analysis. Was analyzed sedimentary macroscopic charcoal from the Taul Mare (TG) peat bog, located in Lapus Mountains, northern Carpathians, Romania. The statistically analyses use a variate ordination method principal component analysis (PCA). The PCA was used to correlate fire regime, charcoal accumulation rate (CHAR), geochemistry, magnetic mineral properties and particle size using PAST4.11 software. Our results show correlation between morphological charcoal (e.g., wood, grass, etc.) in opposition with magnetic mineral properties and particle size having the highest values. This may be interpreted as reflecting climate change caused by anthropogenic activity in special mining having consequence in landscapes with changes in wildfire regime. The main results of PCA point to conclude the following: wildfire increase following anthropogenic activities; increases in wildfire have generally been accompanied by episodes of increased landscape openness and pastoral activities; the study area followed the mid-elevation mountains and proximity to landscape resources, pasture and mining. In conclusion our results show direct connection with statistically significant link between fire severity and magnetic mineral concentration, and direct relation between fires and erosion (regardless of severity). This study can offer information about previously unstudied environmental history in mid-elevation mountains, of the Northern Carpathians and highlights the importance of studies that what can improve our understanding of the fire regime caused by mining activities.

How to cite: Petras, A.: Peat core sequence in the Northern Carpathians, Romania. Fire and mining activities relationship over the late Holocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15079, https://doi.org/10.5194/egusphere-egu23-15079, 2023.