Thermokarst lake and drained lake basin (DLB) dynamics are intensifying across the Alaskan Arctic Coastal Plain. Thawing, drainage, and erosion expose surface and deep sediments (> 1 m) to aerobic conditions, with saline deposits being particularly vulnerable due to freeze-point depression. As organic carbon mineralization remains poorly constrained, we determined potentials with an aerobic one-year long incubation at 10°C in permafrost upland, lake talik, lake cryopeg, and refrozen saline DLB sediments. We linked CO2 production to biochemical, hydrochemical, and microbial factors, and assessed carbon alteration via repeated n-alkane analyses. After 382 days, average CO2 production was 7.0 ± 0.4 mg C g-1 dry weight (DW), with DLB surface peat yielding the most (40.5 ± 2.7 mg C g-1 DW), and carbon-poor cryopeg deposits (1.4 ± 0.1 mg C g-1 DW) and refrozen saline permafrost (1.5 ± 0.02 mg C g-1 DW) the least. Total organic carbon (TOC) was the main driver of CO2 production, while age, nitrogen content, electrical conductivity, water content, pH, and microbial abundance also correlated significantly with CO2 production. Normalizing production to TOC contents, saline permafrost and cryopeg sediments showed similar CO2 production to active layers, stressing the importance of potentially carbon-rich saline deposits. TOC normalization revealed that carbon characteristics (δ13C, alkane content, ACL) also significantly influenced CO2 production. The n-alkane based quantification of carbon alterations during the incubation further contributes to the understanding of carbon cycling at the molecular level. n-Alkane contents increased on average by 153% and the carbon preference index (CPI) rose from 13.2 to 15.8, likely due to newly produced alkanes, preferential degradation, and desorption processes. This indicates strong responses of the carbon pool and raises questions about the reliability of the CPI as a degradation proxy. Altogether, our study highlights the overlooked role of salinity in CO2 production from Arctic coastal plains which could substantially shift carbon balances.

This study investigates the archaeological and geoarchaeological properties of a cultural layer at the Upper Paleolithic site of Zaraysk. We examine the human impact on soil properties within several functional areas using a multiproxy approach including physical, geochemical, and biogeochemical methods. The percentage of organic carbon most likely added by various human activities was estimated by applying a new approach using n-alkane contents and ratios. The results show that human activities led to distinct geoarchaeological signals and that most of the organic carbon in all functional areas is of anthropogenic origin. The flintknapping waste disposal pit contained animal and plant remains, accounting for 54% of the total organic carbon. In the bone-fueled hearth the highest proportion of "anthropogenically"-derived organic carbon (87%) was found. It was associated with fragmented bones, a small amount of wood for ignition, and organic residues from cooking. The floor of the "earth-dwelling" contained a high proportion of "anthropogenically"-derived organic carbon (78%), despite a low content in total organic carbon, and might have been covered by a layer out of animal skins and grass bedding. The surface of the cultural layer was largely a human-made deposit, which included geogenic material excavated from pits and charred material cleaned out from hearths. These findings advocate for the further use of biogeochemical methods at archaeological sites, including Paleolithic contexts, and demonstrate that soil memory - reflected also in soil organic matter - preserves a valuable record of human-environment interaction.

Compound-specific stable hydrogen (SD) and oxygen (S18O) isotopes of aquatic and terrestrial biomarkers in lake sediments are widely used to reconstruct palaeohydrology, recording variations in precipitation and evaporation. The two main approaches are the dual biomarker approach, based on the isotopic differences between SD of aquatic and terrestrial n-alkanes, and the coupled isotope approach, combining n-alkanes (SDn-alkane) with hemicellulose-derived sugars (S18Osugar) to reconstruct deuterium-excess (d-excess). Both are commonly applied in palaeohydrology, but so far, they were never directly compared to each other. We analysed S18Osugar in surface sediments from Lake Khar Nuur, Mongolia, complementing an existing dual biomarker SDn-alkane dataset. The sugar biomarker fucose was identified as an aquatic endmember in the sediments. The S18Ofucose is therefore used as a proxy for S18Olake water, which is modulated by evaporative enrichment of lake water like SDn-C23. Both isotopes significantly correlate and show high evaporative enrichment in the central basins. By coupling the aquatic endmembers SDn-C23 and S18Ofucose, we calculated aquatic d-excess and precipitation SD and S18O. Results closely match those from the dual biomarker approach and precisely align with the local isotopic signature of growing season precipitation. Similar results for d-excess and precipitation were obtained using a modified coupled isotope approach based on terrestrial SDn-C31 and aquatic S18Ofucose. Overall, our results depict the sensitivity of biomarker compounds in the lake's sediment accumulation zone for environmental processes. The methodological comparison confirms the compatibility of dual and coupled isotope approaches and supports their application in molecular palaeohydrology.

In Arctic coastal lowland regions such as northernmost Alaska, thermokarst landscapes are often underlain by saline deposits, a factor frequently overlooked when assessing permafrost thaw risks. To evaluate the influence of thaw and salinity on organic matter degradation and landscape dynamics, we analyzed six sediment cores from representative landforms near Utqia & gdot;vik (Alaska) using a multiproxy, carbon-focused approach, with emphasis on n-alkane biomarkers. Undisturbed tundra uplands contained well-preserved, organic-rich Holocene sediments (similar to 140 cm thick) overlying brackish late Pleistocene deposits, indicating the presence of saline permafrost. Thermokarst lake subsidence into these substrates led to enhanced organic matter degradation, as reflected by lower n-alkane carbon preference index (CPI) values. While West Twin Lake talik sediments exhibited brackish porewater, East Twin Lake sediments were characterized by predominantly saline porewater, indicating the presence of a cryopeg driven by salt-induced thaw-point depression. Lagoonal environments, receiving both terrestrial and lacustrine inputs, accumulate sediments under unfrozen hypersaline conditions, presenting a high potential for organic matter decomposition. Carbon proxy signatures statistically distinguish perennially frozen uplands, unfrozen lake sediments, refrozen drained lake basins, and lagoonal settings. Our results demonstrate that salt-bearing deposits, as found in all investigated sites, are vulnerable to active layer deepening, talik and cryopeg formation, and lake/coastal shoreline erosion. These processes accelerate organic matter degradation and alter landscape trajectories. Our study underscores the need to better understand the role of saline permafrost in Arctic coastal lowlands and its broader implications under ongoing climate change.

The hydrological cycle intensifies under global warming, causing humid areas to become wetter. However, rising temperatures also amplify seasonal ecosystem dryness, complicating the link between temperature and hydroclimate. Such divergent mechanisms challenge generalizations like 'warm and wet' in paleoclimatology on a global scale. On a regional scale, knowledge about evapotranspiration in response to past warming and cooling is still limited, but highly relevant to understand future hydroclimate. Here, we analyse the hydrogen isotope composition (delta D) of aquatic and terrestrial biomarkers in varved sediments from Moossee, Switzerland, covering the past 7300 years at a temporal resolution of 30 years. Based on a dual biomarker approach, we reconstruct evapotranspiration at Moossee. Our data suggests that cool and wet conditions repeatedly favored rising lake levels and advancing glaciers in the Alps but lowered treelines, e.g. at the onset of the Neoglacial, dated to -5.5 cal ka BP. In contrast, warmer periods like the Mid Holocene or the Roman Warm Period were associated with dryness. Short-term hydrological fluctuations are partly explained by volcanic and solar forcings. Aside from an increased risk of strong convective rainfall and floods, paleohydrology provides robust evidence that an intensified hydrological cycle under global warming will substantially favor summer drought in Central Europe.

The Eastern African region is an amalgamation of complex climate systems nestled in contrasting topographic barriers. Although rift basins are prime targets for studying the climate of the past, high-altitude climate archives in the context of paleoclimate research also offer invaluable insight and have yet to be fully explored. Here, we present a 17 kyr hydroclimate history of the Afro-alpine (4121 m a.s.l) Central Lake using a S18O record established by analyzing hemicellulose-derived sugar biomarkers. The sugar biomarker patterns with a dominance of fucose indicate the predominance of autochthonous sedimentary organic matter. Therefore, the oxygen isotopic variability of the sugar biomarkers in general and of fucose in particular (S18Ofucose) reflects S18Olake water being controlled by climatic conditions, particularly lake water 18O enrichment by evaporation. Our S18Ofucose record from Central Lake indicates strong enrichment during the Late Glacial. Around 15 cal kyr BP, the onset of more humid climate marks the beginning of the African Humid Period (AHP) in the Bale Mountains. The AHP was interrupted by an arid period during the Late Glacial - Holocene transition roughly coinciding with the Younger Dryas (YD). After the YD, humid climatic conditions prevailed again until the Late Holocene when a gradual shift towards drier climate started. Our S18Ofucose record and interpretation agree well with the findings from adjacent low-altitude archives of Eastern Africa, the Indian Ocean paleoclimate records and the Asian Monsoon Domain, which suggests region-wide hydro-climatic teleconnections.

Lipid biomarkers are valuable proxies for reconstructing paleoclimate and paleoenvironmental changes as well as human impact. However, little attention has been paid on evaluating how the combination of biomarkers can be used to reconstruct various aspects of local paleoenvironmental conditions. This study presents a suite of lipid biomarker records from a sediment core from Lake Höglwörth, southern Germany, covering the past 400 years. Compound-specific hydrogen isotopic compositions (δD) of terrestrial n-alkanes (n-C29-alkane) and n-alkanoic acids (n-C30-acid) indicate minor changes in isotopic composition of precipitation. The δD of n-C22-acid is interpreted to record the isotopic composition of the lake water and evaporative enrichment, which drops after 1700 CE, coinciding with the construction of a mill and the related rerouting of a creek into Lake Höglwörth. The δD of n-C25-alkane is also enriched but decoupled from the reconstructed isotopic composition of precipitation and lake water. Therefore, we suggest that δD of n-C25-alkane reflects the leaf water isotopic composition of Sphagnum, which is present in the catchment and undergoes transpirative enrichment. Both short-chain compounds have become more enriched over the last century, maybe related to increasing temperature associated with anthropogenic climate warming. The faecal biomarkers record the changes in human population, partly related to the history of the local Monastery, the World Wars I and II as well as the intensive farming after the mid-20th century. Polycyclic aromatic hydrocarbons (PAHs) reveal a significant change in combustion activities associated with human activities such as the industrial revolution, biomass burning, and environmental cleanup as well as the implementation of emission standards. Our study demonstrates that the combination of plant wax compounds, faecal biomarkers, and PAHs from lacustrine sediment serves as a valuable tool to reconstruct and distinguish various aspects of paleoclimate and paleoenvironmental changes including human impacts.

It is generally accepted that a weakening of the North Atlantic thermohaline circulation caused the Younger Dryas cooling. Although the role of seasonality was emphasized previously, this aspect is rarely considered yet, and it remains elusive how this impacted hydroclimate during winters and summers across Central Europe. Here, we coupled biomarker-based δ18O and δ2H from Bergsee in southern Germany to reconstruct deuterium excess as a proxy for evaporation history from the Bølling-Allerød to the Preboreal. We compared this dataset with other biomarker isotope records in Central Europe. They are all lacking a strong isotopic depletion during the Younger Dryas, which is best explained by the summer sensitivity of the biomarker proxies: As Younger Dryas summers were relatively warm, there is an absence of the strong winter cooling signals recorded in annual water isotope records like Greenland or Lake Steißlingen. Lake evaporation at Bergsee together with other paleohydrological reconstructions draw a coherent picture of the Late Glacial hydroclimate, with strong evidence for warm and dry Younger Dryas summers. Rather than a southward shift of the Westerlies during winter, we suggest that a recently proposed feedback mechanism between North Atlantic sea ice extend, strong winter cooling and summer atmospheric blocking serves as a suitable explanation for summer dryness. Additional confidence to the robustness of these biomarker records is provided by the overall agreement of paleohydrological fluctuations during the Preboreal.

The Sanetti Plateau is Africa's largest Afro-alpine ecosystem. As part of an ongoing effort to reconstruct the paleo-extent of Ericaceous vegetation in this ecosystem, we aim to identify unambiguous Erica biomarkers. Here, we present a respective study focusing on plant-derived terpenoids. Terpenoids from seven keystone plant species were identified and quantified using gas chromatography-mass spectrometry (GC-MS). Widely employed angiosperm biomarkers such as lupane, oleanane, ursane, and taraxastane-type triterpenoid alcohols, acids, and esters were detected with a more ample presence in Erica species and Lobelia rhynchopetalum. Ursolic acid is always the predominant triterpenoid, followed by oleanolic acid. The beta- and alpha-amyrin triterpenoids allowed distinguishing Erica trimera from the other plants in hierarchical cluster analysis (HCA). The nearly exclusive presence of amyrin acetate in particular and the total terpenoid content in Erica species corroborate the potential of terpenoid biomarkers for reconstructing the paleo-extent of Ericaceous vegetation in the soil and sediments. Moreover, 3beta-taraxerol may serve as a proxy to distinguish the morphologically and ecologically very similar Erica trimera and Erica arborea. Given that the diagenetic alteration of taraxerol as well as other terpenoid biomarkers should not be overlooked, ongoing research is needed and encouraged to address this issue.

Fire is a natural phenomenon along South Africa's southern Cape coast, but identifying its climatic drivers has been a subject of considerable debate. This study investigates the hydroclimatic and fire dynamics from a 9.6 m sediment core from Vankervelsvlei covering the past 7.2 ka. The fen is located near the southern Cape coast within the year-round rainfall zone of South Africa. A reconstruction of hydroclimatic variability through time applies oxygen isotopes from hemicellulose-derived sugars and hydrogen isotopes from leaf wax-derived n-alkanes. Coupling both isotopes enables a reconstruction of the atmospheric source and seasonality of precipitation as well as estimating local relative humidity. Past trends in fire activity are inferred from macro-charcoal and polycyclic aromatic hydrocarbon (PAH) analyses, the latter serving as fire biomarkers. Results indicate high fire activity at Vankervelsvlei accompanied by generally moist conditions and a yearround rainfall regime linked to both Westerly-derived winter precipitation and Easterly- and locally-derived summer precipitation from 7.2+0.2/_ 0.2 to 4.5+0.3/_ 0.3 cal ka BP. From 4.5+0.3/_0.3 to 1.5+0.4/_0.2 cal ka BP, a shift to a Westerly-derived winter rainfall regime is identified. This variation features alongside reduced fire activity and persistent drought conditions as Easterly- and locally-derived summer precipitation decreased. From 1.5+0.4/_0.2 cal ka BP until present day, macro-charcoal and PAH accumulation rates show high fire activity. Paleoclimate evidence from the last two millennia suggests a variable climate with an overall increase in total moisture availability as contributions from both Westerly-derived winter precipitation and Easterly- and locallyderived summer precipitation support the year-round rainfall regime present today. Results from Vankervelsvlei support previous evidence from regional paleo-reconstructions, refining our understanding of the interplay between hydroclimatic variability and fire activity along South Africa's southern Cape coast. Our study discusses the role of large-scale climate modes, specifically the intensity of El Nin similar to o, as a potential driver of short-term hydroclimatic variability, which in turn drives fuel availability and fire activity at Vankervelsvlei during the Holocene.

Peatlands are receiving increasing attention in palaeoenvironmental research and represent very useful terrestrial archives for reconstructing vegetation, climate and human history. Previous palaeoenvironmental studies in the Fotsch Valley, Stubai Alps, Austria, focused on geoarchaeological investigations on the Ullafelsen representing a very important prehistorical encampment site used by Mesolithic hunter-gatherers (10.9–9.5 cal. kyr BP). In order to contribute to a better understanding of the landscape evolution of the Fotsch Valley, we here studied the close-by subalpine ‘Potsdamer Hütte Mire’ by applying radiocarbon dating as well as elemental, biomarker, compound-specific stable isotope, palynological and macrofossil analyses on bulk peat samples. The calculated age-depth model using R Bacon indicates the beginning of peat formation during the Early Holocene and shows a strongly reduced peat accumulation rate (PAR) from 170 to 121 cm depth (8.5–2.1 cal. kyr BP) and/or a striking hiatus. Results of leaf wax-derived n-alkane biomarkers as well as macrofossils and palynological indicators reflect the local presence of coniferous trees and the synchronous expansion of deciduous trees during the Early Holocene. The above-mentioned strongly reduced PAR and/or hiatus coincides with the Neolithic, the Bronze and the Iron Age, and goes hand in hand with strong changes in vegetation and an increase of micro-charcoal and black carbon. Despite age uncertainties, these changes can be explained with strongly increasing human and livestock activities in form of deforestation, domestic fires and the beginning of Alpine pastoralism. The latter is confirmed by the finding of pasture and cultural indicator pollen (Cerealia-type, Rumex, Plantago lanceolata, Poaceae) occurring since the Middle to Late Bronze Age. The oxygen isotope composition of sugar biomarkers (δ18Osugars) likely reflects the dry versus humid climatic variability associated with the Holocene climatic optimum during the Mesolithic, the Roman Age, the Late Antique Little Ice Age, the Middle Ages and the Little Ice Age.

In the Bale Mountains, the ericaceous belt ranges between 3200 and 3800 m asl. Studies indicate an expansion on the Sanetti Plateau at the end of the Late Glacial and during the early Holocene. Currently, only patches of Erica growing between boulders are found on the Plateau, while most of the landscape above 3800 m asl is covered by afro-alpine plants. Driving factors for Erica patches above the upper ericaceous ecotone is a matter of debate. This study evaluates site variables and biogeochemical properties of soils under Erica patches and nearby Erica -free control to understand the environmental conditions responsible for the patchy occurrence of Erica on the Sanetti Plateau. Except for the boulder richness, Erica and control plots have comparable topography, soil texture, and electrical conductivity. However, soils below Erica patches have higher total organic carbon, nitrogen, carbon-to-nitrogen ratios, and black carbon contents than the control plots indicating fresh organic matter input and availability of combustible fuel. This implies that Erica did not fully cover the control plots in former times. Carbon and nitrogen stocks were slightly higher in control plots due to the lower stone contents of the profiles. In addition, soils of the Erica plots showed more positive δ 13 C values than the control soils, possibly attributed to water stress. In general, the relief and soil conditions of control plots may support the growth of Erica . However, Erica growing between boulders seems to benefit from the favorable microclimate and physical protection against grazing and fire.

Snow petrels (Pagodroma nivea), which are endemic to the Antarctic region, produce proventricular stomach oil from ingested food for feeding purposes but also spit the oil in the immediate surrounds of the nests, where it forms encrustations over time (Antarctic mumiyo). These deposits provide a unique opportunity to understand the paleo-ecological diet of snow petrels and because the seabirds forage in the ocean, they potentially provide an archive of past marine environmental conditions in the Southern Ocean. For validating methods for reconstructions we use compositional data obtained on modern stomach oils and DNA data from fecal samples of snow petrels. We find that the distribution of carboxylic acid compounds in modern stomach oils and in the fossil deposits are consistent with variable contributions of fish and krill, which are the main constituents of modern snow petrel diet, and allows inference of past changes in snow petrel diet from the fossil record. Analyses of mumiyo deposits from six regions in East Antarctica reveal systematic differences in the isotopic composition of organic matter (d(13)C and d(15)N) and carboxylic acid patterns. This may suggest regional and/or temporal variability in the composition of snow petrels diet, likely differing in response to the prevailing environmental conditions in the foraging range of the birds, such as sea-ice variability, polynya activity and primary productivity. Our study provides confidence for using these approaches for broader scale paleo-studies in the future and for an assessment of the temporal changes and regional variability in snow petrel diet.

Isotope-based records provide valuable information on past climate changes. However, it is not always trivial to disentangle past changes in the isotopic composition of precipitation from possible changes in evaporative enrichment, and seasonality may need to be considered. Here, we analyzed δ 2 H on n -alkanes and δ 18 O on hemicellulose sugars in sediments from Bichlersee, Bavaria, covering the Late Glacial and Early Holocene. Our δ 2 H n -C31 record documents past changes in the isotopic composition of summer precipitation and roughly shows the isotope pattern known from Greenland. Both records show lower values during the Younger Dryas, but at Bichlersee the signal is less pronounced, corroborating earlier suggestions that the Younger Dryas was mainly a winter phenomenon and less extreme during summer. δ 18 O fucose records the isotopic composition of the lake water during summer and is sensitive to evaporative enrichment. Coupling δ 2 H n -C31 and δ 18 O fucose allows calculating lake water deuterium-excess and thus disentangling changes in the isotopic composition of precipitation and evaporative enrichment. Our deuterium-excess record reveals that the warm Bølling–Allerød and Early Holocene were characterized by more evaporative enrichment compared to the colder Younger Dryas. Site-specific hydrological conditions, seasonality, and coupling δ 2 H and δ 18 O are thus important when interpreting isotope records.

Organic matter in sedimentary archives is abundantly used to reconstruct paleoenvironmental and climate histories. Thereby, distinguishing between the terrestrial and aquatic origin of sedimentary organic matter is often a prerequisite for robust interpretations. In this case study, we use published data for modern plants and topsoils to identify the terrestrial versus aquatic source of n -alkane and sugar biomarkers in two afro-alpine sediment archives (Lake Garba Guracha and Depression B4) in the Bale Mountains, Ethiopia. The results of our comparative approach show that the long-chain n -alkanes C 29 , C 31 , and C 33 in the sedimentary archives yielded patterns similar to those typical for the potential terrestrial input. By contrast, the relative abundances of the sedimentary mid-chain n -alkanes C 23 and C 25 , and at least partly C 27, are significantly increased compared to the plants and topsoils. This suggests that they are primarily produced by aquatic macrophytes and micro-organisms. The P aq ratio (C 23 + C 25 )/(C 23 + C 25 + C 29 + C 31 ) is validated as a suitable source identification proxy in our study area. The sugar biomarkers xylose (xyl) and arabinose (ara) are abundant in the plant and topsoil samples. By comparison, high relative abundances of fucose (fuc) and rhamnose (rham) are generally only observed in sediments. This indicates that these sugar biomarkers are primarily produced by aquatic macrophytes or micro-organisms. Therefore, the ratio (fuc + rham)/(ara + xyl) is a suitable sugar biomarker proxy for organic matter source identification. The relative abundances of galactose and mannose are systematically decreasing and increasing, respectively, from leaves over O-layers to Ah-horizons. Furthermore, they are not significantly different from the abundances found in the sediments. This hinders terrestrial versus aquatic source identification using galactose and mannose.

<p>The oxygen and hydrogen isotopic composition δ<sup>2</sup>H and δ<sup>18</sup>O of leaf and lake water reflects the isotopic composition of source water/precipitation modified by evapo(transpi)rative enrichment. This later enrichment can be illustrated and quantified using δ<sup>2</sup>H- δ<sup>18</sup>O diagrams and the deuterium-excess. The enrichment of leaf water thereby depends primarily on relative air humidity (RH) and can be investigated using biomarkers being produced in leaves. The enrichment of lake water depends on lake evaporation and can be investigated using biomarkers being produced by aquatic macrophytes or algae. Provided that unambiguous terrestrial and aquatic biomarkers can be identified in lake sediments, the coupling of δ<sup>2</sup>H and δ<sup>18</sup>O hence allows reconstructing RH (paleohygrometry approach) and lake evaporation history. In our contribution, we discuss the potential, the advances and the limitation of the coupled isotope approach based on leaf wax-derived <em>n</em>-alkane and hemicellulose-derived sugar biomarkers (δ<sup>2</sup>H<em><sub>n</sub></em><sub>-alkanes</sub>-  δ<sup>18</sup>O<sub>sugars</sub>).</p> <p> </p> <p>References</p> <p>Hepp, J., Mayr, C., Rozanski, K., Schäfer, I., Tuthorn, M., Glaser, B., Juchelka, D., Stichler, W., Zech, R. and Zech, M., 2021. Validation of a coupled δ<sup>2</sup>H<em><sub>n</sub></em><sub>-alkane</sub>-δ<sup>18</sup>O<sub>sugar</sub> paleohygrometer approach based on a climate chamber experiment. Biogeosciences 18, 5363-5380.</p> <p>Hepp, J., Wüthrich, L., Bromm, T., Bliedtner, M., Schäfer, I. K., Glaser, B., Rozanski, K., Sirocko, F., Zech, R., and Zech, M., 2019. How dry was the Younger Dryas? Evidence from a coupled δ<sup>2</sup>H-δ<sup>18</sup>O biomarker paleohygrometer applied to the Lake Gemündener Maar sediments, Western Eifel, Germany, Climate of the Past 15, 713-733.</p> <p>Zech, M., Tuthorn, M., Detsch, F., Rozanski, K., Zech, R., Zöller, L., Zech, W. and Glaser, B., 2013. A 220 ka terrestrial δ<sup>18</sup>O and deuterium excess biomarker record from an eolian permafrost paleosol sequence, NE-Siberia. Chemical Geology 360-361, 220-230.</p>

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 δ18Osugar extracted from organic matter derived sugar biomarkers in high resolution (every 4 cm). The δ18Osugar record 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.ReferencesBittner, 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.

The compound‐specific hydrogen isotopic composition (δ2H) of n‐alkanes is a valuable proxy to investigate hydrological conditions in lake sediments. While terrestrial n‐alkanes reflect the isotopic signal of the local precipitation, aquatic n‐alkanes incorporate the isotopic signal of the lake's water, which can be strongly modulated by evaporative enrichment. So far, the spatial distribution of the terrestrial and aquatic δ2H signal within lakes have not systematically been investigated. Here, we present compound‐specific δ2H results of terrestrial (δ2HC31) and aquatic (δ2HC23) n‐alkanes of surface sediment samples from Lake Khar Nuur, a semi‐arid and high‐altitude lake in the Mongolian Altai, and additionally investigate the δ2H signal of topsoils from the catchment. Our results show that the majority of the n‐alkane δ2H values from the catchment topsoils correspond well with modeled local growing season precipitation (JJAS). However, few samples in the northern catchment show more positive δ2H values possibly due to increased evapo(transpi)ration by southward exposition and shallower soils there. The only small variability of δ2HC31 in the surface sediments is in the range of most topsoils δ2H from the catchment, and thus, well reflects local growing season precipitation. δ2HC23 in surface sediment samples from the central and deepest parts of the lake, that is, the lake's sediment accumulation zones, shows distinctly more positive δ2HC23 values due to evaporative lake water enrichment. Consequently, Δaq‐terr, which is the isotopic offset between δ2HC23 and δ2HC31, indicates distinct lake water enrichment in the lake's accumulation zones and is a valuable proxy to investigate past hydrological changes.