Compound-specific stable isotope analysis (CSIA) of organic biomarkers enables reconstruction of past environmental and climatic conditions by resolving the isotope composition of individual molecular compounds. Among these applications, hydrogen isotope (δD) measurements of leaf wax n-alkanes are widely used to infer changes in hydroclimate, including variations in precipitation isotopic composition, moisture source, and evaporative conditions. Because long-chain n-alkanes are resistant to degradation and preserve a terrestrial signal in sedimentary archives, their δD values provide a robust proxy for past continental hydroclimate across a wide range of depositional settings.

Despite this utility, CSIA of organic biomarkers is frequently limited by the low abundance of target compounds, particularly in sedimentary archives where concentrations vary strongly across stratigraphy and compound class. This limitation is especially acute for δD measurements, which typically require injected analyte masses of several hundred nanograms to achieve acceptable precision on gas chromatography-isotope ratio mass spectrometry (GC-IRMS) systems. Because hydrogen isotope analysis relies on pyrolytic conversion to H₂, δD measurements generally operate at lower absolute signal intensities than compound-specific δ¹³C analyses, placing them closer to instrumental sensitivity limits where background correction, baseline placement, and nonlinear response exert a proportionally greater influence on measured isotope ratios. As a result, δD analysis of individual low-abundance compounds is often precluded, necessitating pooled samples or coarse sampling intervals that suppress short-duration climate signals and limit the achievable resolution of paleoclimate reconstructions.

Here, we assess the feasibility, limitations, and uncertainty structure of isotope dilution (ID) for δD measurements of leaf wax n-alkanes using internationally recognized, isotopically characterized n-alkane standard mixtures. Isotope dilution offers a potential strategy to stabilize isotope measurements through controlled mixing of a low-abundance analyte with an isotopically characterized spike, thereby increasing the total amount of analyte contributing to the measurement and reducing uncertainty associated with low signal intensities. Controlled mixing experiments isolate the effects of nominal mixing ratio, isotope contrast between spike and sample, and signal intensity on back-calculated isotope values. These tests provide a framework for quantifying uncertainty propagation in ID-CSIA and for defining practical constraints on its application. Our results establish conditions under which isotope dilution can yield accurate and precise δD measurements for low-abundance compounds and provide methodological guidance for extending CSIA into concentration regimes that are otherwise analytically inaccessible, enabling higher-resolution paleoclimate reconstructions and expanding the range of sedimentary archives amenable to biomarker isotope analysis.

How to cite: Lupien, R., Traphagan, J., and Juchelka, D.: Isotope dilution to enhance δD measurability in low-abundance n-alkane samples, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7259, https://doi.org/10.5194/egusphere-egu26-7259, 2026.

The Tortonian stage (11.6–7.2 Ma) represents a warm interval preceding the Late Miocene Cooling (7.5–5.5 Ma), during which high-latitude temperatures exceeded modern values by up to ~17°C. Atmospheric CO₂ reconstructions during the Tortonian are poorly constrained, with existing proxy records suggesting either high CO2 levels, reaching ~790 ppm at ~11 Ma (Mejia et al., 2017), or more moderate and relatively stable CO₂ conditions.

Here, we present new high-latitude pCO₂ reconstructions based on alkenone carbon isotopic fractionation (ε_p) from Ocean Drilling Program (ODP) Site 1088 in the subantarctic South Atlantic, covering the interval from 11.6 to 9.0 Ma. Combined benthic and bulk carbonate δ¹³C and δ¹⁸O records are used to identify the Tortonian thermal maximum and to guide targeted, higher-resolution sampling. Sea surface temperatures are reconstructed from alkenone Uk′₃₇ ratios using the Bayspline calibration (Tierney et al., 2018), and ε_p is calculated from compound-specific δ¹³C measurements of the C_37:2  alkenone. The isotopic composition of dissolved inorganic carbon is estimated from planktonic foraminiferal (G. bulloides) δ¹³C, accounting for the temperature-dependent fractionation between DIC and aqueous CO₂.

pCO₂ concentrations are then reconstructed using a probabilistic ε_p model (Stoll et al., 2019) that explicitly incorporates coccolithophore cell size, growth rate, and light availability. Coccolith size and thickness distributions are quantified from circular polarized image analyses, while growth rates are inferred from temperature and nutrient availability.

How to cite: Santos, M., Wijker, R., and Stoll, H.: Reconstructing sea surface temperature and atmospheric CO₂ across the Tortonian using alkenone εp records from South Atlantic ODP Site 1088, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7288, https://doi.org/10.5194/egusphere-egu26-7288, 2026.

Certain haptophyte algae produce a recalcitrant suite of long-chain (C₃₇-C₃₉) methyl and ethyl ketones called alkenones. These compounds are widely applied in paleoclimate studies due the temperature sensitivity of the ratio of di- to tri- unsaturated alkenones, most commonly quantified in the U^K’₃₇ index. However, phylogenetic effects and other physiological effects can alter the intercept of the U^K’₃₇ relationship to temperature, complicating the application to past climates. Here we present results of two strains of Group II (brackish) and four strains of Group III (open marine) haptophytes batch cultured under different temperatures, light levels, and CO₂ (aq) concentrations. One Group III strain was also continuously cultured in a turbidostat.

The alkenone response to temperature differs per strain, as has previously been found in culture studies. Additionally, when applying core top calibrations commonly used in paleoclimate studies, U^K’₃₇ consistently under-predicts batch culture growth temperature. We further find no systematic control on the offset between alkenone unsaturation calibrations from core top and expected values in batch culture for a given strain. When considering data from multiple strains, the offset from expected values in U^K’₃₇ and U^K_38Me, but not U^K_38Et, correlate to ratio of the alkenone concentration relative to particulate organic matter. In cells harvested with a higher proportion of alkenones relative to particulate organic carbon, this cold offset is diminished and temperature prediction for U^K’₃₇ and U^K_38Me is more consistent with core top calibrations.

In addition, we compare nutrient replete continuous culture results to batch culture of the same strain to assess if the alkenone unsaturation response to temperature similar.

How to cite: Rice, A., Torres-Romero, I., Zhang, H., Wijker, R. S., Clark, A. J., Jaggi, M., and Stoll, H. M.: Phylogenetic effects of alkenone unsaturation in cultured Group II and Group III haptophytes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7314, https://doi.org/10.5194/egusphere-egu26-7314, 2026.

Climate models are based on our understanding of the Earth climate system. To improve their accuracy, we rely on regional paleotemperature reconstructions, that can also be used to validate model outputs. Many existing paleoclimate proxies reconstruct mean annual or summer temperatures. Spring, which is essential for biodiversity and agricultural activities, is underrepresented, resulting in an incomplete perception of past climate, especially regarding seasonal variations. Lacustrine alkenones are lipid biomarkers that appear as a promising paleothermometer to quantitatively record spring temperatures in freshwater lakes. They are long chain ketones (35 to 42 carbons) with a varying number of double bonds (2 to 4) produced exclusively by the haptophyte phytoplankton in the Order Isochrysidales. These algae were found to respond to water temperature changes by altering relative proportions of the produced alkenones. The UK37 index has been extensively used to reconstruct sea surface temperatures in the past. Alkenone producing algae are divided into three major phylogenetic groups shaped largely by salinity. Among these groups, Group I dominate freshwater lakes, making them potential powerful tools for reconstructing continental spring temperatures. Alkenone seasonality was resolved in several studies conducted in high-latitude lakes which found alkenones occurring at the ice-off (spring-summer). The question arises regarding which seasonal temperatures are recorded by the UK37 index in mid latitude lakes? When other proxies show great uncertainty, three robust in-situ calibrations with low uncertainties were developed for the correlation of UK37 values to temperatures in high-latitude lakes. However, so far, no monitoring studies have been conducted in mid-latitude lakes, and no in-situ calibration has been established. Therefore, we conducted high-frequency monitoring of alkenone production in two Swiss lakes with very distinct settings for comparison: Greifensee (453masl, lowland and not ice-covered), and Lake St. Moritz (1768masl, alpine and ice-covered). The monitoring consisted in taking water samples over a full year on Greifensee, and from spring to summer in Lake St. Moritz, and retrieving sediment traps regularly to study alkenone deposition into the sediments in parallel with production in the water. We also collected environmental data such as salinity, nutrient contents, chlorophyll concentrations, temperature, and light radiation. We describe the seasonality of alkenone production in these two lakes and draw the first calibrations between the UK37 and temperature. The timing of alkenone production will be compared with variations in the environmental parameters to estimate the bloom drivers. With this work, we aim to establish a reliable continental spring temperature proxy. 

How to cite: Marchand, L., Martin, C., Richter, N., Amaral-Zettler, L., and Dubois, N.: Seasonality of Group I alkenone production and in-situ UK37-Temperature calibrations for mid-latitude Swiss lakes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1451, https://doi.org/10.5194/egusphere-egu26-1451, 2026.

Present-day biodiversity and landscapes in Europe reflect millennia of human influence. Particularly, the ‘medieval agricultural revolution’ marked large-scale movements of people, plants, and livestock, and major shifts in agricultural practices, coinciding with the Medieval Climate Anomaly. Understanding how this biodiversity emerged, and how it contributes to the resilience of socio-ecological systems is critical for future climate-adaptive land-use planning and management. Existing human-ecodynamic reconstructions are largely based on archaeological sites and mires, and therefore often lack the spatial representativeness beyond an individual site, continuous depositional archives, or the temporal resolution and ecological breadth needed to assess biodiversity, land-use history, and species vulnerability in detail.

The ERC synergy project “MEMELAND – Molecular Ecology of Medieval European Landscapes” addresses these gaps through an interdisciplinary multi-lake, multiproxy framework. As part of this project, we will investigate lake sediment records from 50 lake pairs across a latitudinal gradient in Europe. Each pair consists of one lake located near a high-status (elite) site and one “control” lake from a nearby area lacking direct archaeological evidence for medieval elite activity. Such baselines from nearby “pristine” lakes are rarely established but are essential for disentangling natural from anthropogenic drivers of change.

Here we present our faecal biomarker framework to reconstruct grazing and manuring intensity during the medieval period using sterols, stanols, and bile acids measured as concentrations and depositional fluxes. To improve source attribution, we are developing a diet-controlled livestock reference library that characterizes sterol/stanol and bile-acid fingerprints and diagnostic ratios under historically plausible feeding regimes. We further leverage MEMELAND’s sedaDNA component to benchmark biomarker-derived livestock inputs against taxonomically resolved signals of domestic animals and land-use indicators. In this complementary approach, faecal biomarkers constrain the magnitude of livestock input, while sedaDNA refines the source and ecological context.

We ask which faecal biomarkers and diagnostic ratios are most robust across heterogeneous European lake systems, whether paired-lake comparisons reveal consistent spatio-temporal contrasts in land use during the medieval period, and whether eutrophication trajectories track enhanced nutrient loading associated with grazing and manuring. Besides the sedaDNA data, biomarker results are further integrated with palynological proxies, hyperspectral imaging, geochemistry (µXRF), and chronostratigraphic approaches to identify and contextualize land-use signatures in sediment archives.

On our poster, we present an overview of this biomarker contribution to MEMELAND and look forward to discussing it with you.

How to cite: Schneider, T., Brown, A. G., Mackay, H., Lang, A., Hamerow, H., Mottl, O., and Dubois, N.: Sedimentary faecal biomarkers in European lakes: tracing land-use activity during the medieval agricultural revolution, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7602, https://doi.org/10.5194/egusphere-egu26-7602, 2026.

The Mongol Empire (13^th - 14^th century CE) was the largest contiguous land empire in world history. However, it is not yet known how an urban lifestyle in its first capital Karakorum was sustained in the heart of the Mongolian steppe. One aspect of this is how food supply and subsequent delivery of raw materials was secured.

Therefore, we aimed at characterizing soil resources in Sarlag Tolgoi, an ancient settlement about 50 km northwest of Karakorum. We took samples of a transect through the settlement and reference samples of undisturbed soil, serving as control. We (i) analyzed these samples regarding their phosphorus concentration as waste marker and (ii) the sterol and bile acid concentration in cases where phosphorus levels were elevated, in order to reconstruct past settlement structures and the fingerprint they left on the surrounding environment.

We found a tenfold increase of phosphorus concentrations from 2 to 20 mg P kg^-1 in the topsoil from the surrounding area compared to the soil within the settlement itself. This clearly supports the hypothesis of anthropogenic influence at this site. A closer examination of those samples with increased phosphorus concentration by sterol and bile acid analysis revealed hotspots of an ancient faecal input by grazing animals - mainly cattle and sheep - within the settlement. Furthermore, the applied ratio (epi-5β-stigmastanol/5β-stigmastanol + epicroprostanol/coprostanol) revealed no indication of faecal input from horses, whereas low proportions of coprostanol suggested limited human faecal input. Therefore, we suppose that horses and ditches for human waste were outside of the settlement area.

In conclusion, our results demonstrate that Mongolian steppe soils preserve ancient fingerprints of human settlement associated with the Mongol Empire, expressed through changes in both, their morphology, and chemical signature. These findings highlight the considerable potential of basic soil science approaches to refine and strengthen archaeological interpretations in this region. Moreover, complementary chemical analyses provide valuable insights into past lifeways and human-environmental interactions. While the unambiguous attribution of signals to specific historical periods remains challenging, future integration of compound-specific biomarker dating in the vicinity of archaeological findings holds strong promise for achieving more robust chronological resolution.

How to cite: Koch, I., Mörchen, R., Bemmann, J., Reichert, S., and Amelung, W.: Reconstruction of ancient land-use in the Orkhon Valley, Central Mongolia, by waste markers: phosphorous, sterol and bile acid analyses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9870, https://doi.org/10.5194/egusphere-egu26-9870, 2026.

During the recent decades, human activity led to vast and rapid changes in algal communities through pollution, alteration of catchment areas and climate change. As a consequence of such stressors, lake conditions can offer favourable conditions for the formation of harmful algal blooms (HABs) of cyanobacteria. The rise of bloom-forming taxa and toxin-producing taxa are threatening ecosystem services provided by lakes. Understanding the dynamic nature of algae and these stressors is crucial for developing effective mitigation strategies to preserve or potentially restore the integrity of aquatic ecosystems. Monitoring data is limited to a relatively recent period and thus sedimentary proxies facilitating the reconstruction of past cyanobacteria abundances are necessary to provide historical context for modern observations.

Recently, the phytol:sterol index (PSI), which corresponds to the ratio of phytol (produced by all algae including cyanobacteria) and specific phytosterols (produced only by eukaryotic algae) was proposed as a proxy for the relative abundance of cyanobacteria within the overall algal community (Klatt et al., 2025). Here, we aim to test the suitability of the PSI alongside other emerging sedimentary proxies to record cyanobacteria abundances and the abundance of HABs. To this end, we extracted short cores covering the past ~250 years from two of the Finger Lakes, Owasco and Skaneateles, in Upstate New York (USA) using a universal coring system in spring 2024. While Owasco Lake has experienced progressive eutrophication since the 1960s, nearby Skaneateles Lake with a much smaller watershed to lake surface area ratio remains oligotrophic. HAB occurrences in Owasco began several years before Skaneateles, but since 2017, HABs have occurred in both lakes, with greater prevalence in Owasco.

Bulk sediment analyses (% total organic carbon, C/N ratios) indicate an increase of algae productivity coinciding with the reported progressive eutrophication of Owasco Lake, while Skaneateles Lake shows rather stable conditions. This stability is also reflected in the PSI, which is about 0.25 in Skaneateles Lake throughout our record, indicating relatively low abundance of cyanobacteria. In Owasco Lake, on the other hand, PSI values reveal a marked increase to 0.45 after ~1950, consistent with a shift in community composition towards Cyanobacteria mid-20^th century. We compare these results to compound-specific hydrogen isotope measurements of fatty acids and phytol, and the offsets between them, to further distinguish ecological changes in the lakes. Finally, we use sedimentary DNA (sedDNA) metabarcoding to validate our lipid data by assessing changes in the phytoplankton community and to identify the presence of bloom forming taxa. Overall, the combined results of our proxies are in accordance with observations, and further extend our knowledge of algal community composition prior to the monitoring period. This emphasises the potential of this proxy and the strength of multiproxy approaches.

Klatt, A., De Jonge, C., Nelson, D.B., Reyes, M., Schubert, C.J., Dubois, N., Ladd, S.N., 2025. Algal lipid distributions and hydrogen isotope ratios reflect phytoplankton community dynamics. GCA 394, 205–219. https://doi.org/10.1016/j.gca.2025.02.013

How to cite: Wietelmann, T., Nelson, D. B., Dutta, M., Leon, N., Wood, D., Scholz, C., Thomas, E., and Ladd, S. N.: Assessing sedimentary proxies to reconstruct the occurrence and extent of harmful algal blooms, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17853, https://doi.org/10.5194/egusphere-egu26-17853, 2026.

Lakes are key components of global carbon cycling, accounting for 6-16 % of natural methane (CH₄) emissions. Methane release from lakes is largely regulated by aerobic methane oxidizing bacteria (MOB), which oxidize up to 75% of the methane produced in lakes to CO₂. Over the past two centuries, anthropogenic environmental change and climate forcing have led to rapid changes in lake systems including eutrophication and stronger stratification. The implications of these ongoing processes for MOB communities and the key methane sink they represent remains unclear. A deeper understanding of how MOB communities in lakes responded to systemic change in the past is essential for discerning their future dynamics. This highlights the need for a reliable biomarker that can track changes in MOB communities in lakes across timescales. The hopanoid bacterial membrane lipids, bacteriohopanepolyols (BHPs), exhibit specificity to MOB types and genera, therefore holding potential as biomarkers allowing us to track community assemblages. The peri-alpine lake Rotsee, located in central Switzerland, is a prime example of a monomictic eutrophic lake, making it an ideal study site to further understand and develop BHPs as biomarkers for MOB communities. Here we present initial results of a seasonal study of Rotsee where we used BHPs coupled with eDNA to investigate the MOB assemblages in the lake’s present-day water column, allowing us to ascertain how rapidly seasonally changing conditions affect MOB communities and the lipid biomarker assemblages they produce. We carried out intact polar lipid (IPL) extraction on suspended particulate matter (SPM) filtered from Rotsee’s 16-meter-deep water column at three-meter intervals and at the oxycline, from August 2025 to January 2026, and at two depths (surface and 15 meters) from May to December 2019. IPLs were measured on an Ultra High Precision Liquid Chromatography-Quadrupole-Orbitrap High-Resolution Mass Spectrometer (UHPLC-Orbitrap-HRMS). Genetic material was extracted from the SPM samples and sequenced targeting bacterial 16S rRNA. Preliminary results show that MOB-specific BHPs: aminotriol, aminotetrol, and aminopentol, are present in the Rotsee water column. The relative abundances of BHPs in the epilimnion remains low and steady during spring and summer but spike during lake overturn in November, whereupon most of the methane is released and oxidized after accumulation in the hypolimnion. 16S rRNA data indicates that the MOB communities are entirely made up of Gammaproteobacteria and match BHP seasonal trends with MOB-specific sequences being more abundant during overturn in the surface water. Additionally, surface waters in November are characterized by a higher abundance of aminopentol, which is scarcely found during spring and summer. Interestingly surface water 16S rRNA data also show that the MOB community compositions change considerably in November and December, shifting from Methylomonas to Methylobacter-dominated. Therefore, preliminary results show that BHP abundances respond to seasonal MOB blooms and show promise towards tracking seasonal community dynamics in eutrophic stratified lakes.

How to cite: Cellino, L., De Jonge, C., Ajallooeian, F., Dubois, N., and Richter, N.: Lipid Biomarkers Respond to Seasonal Blooms of Methane Oxidizing Bacteria in a Eutrophic Lake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9089, https://doi.org/10.5194/egusphere-egu26-9089, 2026.

Rising atmospheric CO₂ levels are enhancing primary production, which could result in higher carbon sequestration in biomass (C-fixation). This higher primary productivity, however, relies on a sustained supply of soil nutrients, particularly nitrogen (N). To understand whether climate change and rising CO₂ levels have an impact on soil nitrogen availability on centennial to millennial timescales, a geological perspective can be used. For instance, the glacial-interglacial warming, and Holocene warm periods provide valuable natural analogues for investigating these long-term interactions. However, currently no quantitative methods exist to reconstruct soil nitrogen availability through time. To address this, we propose to develop novel proxies based on lipid biomarkers for essential processes in the soil N-cycle.

In aquatic systems, microbial membrane lipids are well established as biomarkers for specific steps in the N-cycle: for instance, heterocyte glycolipids (HGs), produced by heterocytous cyanobacteria, indicate biological nitrogen fixation. Further, microbial intact polar lipids (IPL), isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) and bacteriohopanepolyols (BHPs) are promising proxies for archaeal ammonia oxidation and bacterial nitrite-oxidation, respectively. We propose to test for these N-cycle biomarkers in soils. A pilot sample set of European surface soils was selected, consisting of both N-limited (N-) dryland (n = 8) and N-replete (N+) grassland soils (n = 4). Lipid extracts were analysed by UHPLC-HRMS to generate a high-resolution dataset of the complete lipidome. As a first step in the proxy development, we here present the BHP composition and changes in their relative distribution between in N- and N+ soils.

A total of 47 different BHPs were tentatively identified. In all samples, hydroxy BHPs are predominant components (50-60%). BHtetrol (BHT) is most abundant and all samples contain BHpentol and BHhexol. Amino-BHPs are less abundant in N- soils compared to N+ (2-7%; 10%). For example, aminotriol BHP is relatively increased in N+ soils. A total of 22 nucleoside BHPs were identified with either an adenine (adenosylhopanes) or inosine (inosylhopanes) headgroup that differ in amount and position of methylation on the BHP core or in the headgroup structure. Adenosylhopanes are relatively more abundant in N- than N+ soils (N-: 40-45%, N+: 20%). Inosylhopanes are present at a lower abundance, with 0-5% in N- and up to 10% in N+ soils. Based on changes in their occurrence, four adenosylhopanes and two inosylhopanes are tentatively proposed as N-cycle biomarkers. Specifically, three adenosylhopanes (diMe-adenosylhopane, diMe-adenosylhopane-headgroup-Me, Me-adenosylhopane-headgroup-diMe) and one Me-inosylhopane are exclusively found in N- soils. Likewise, an early adenosylhopane-headgroup-Me and an inosylhopane-headgroup-diMe only occur in N+ soils.

These results highlight the potential N-cycle lipid biomarkers in soils. The occurrence of other potential biomarkers (isoGDGTs, HGs) for the N-cycle will be tested for on the same soils. Moreover, we will apply an untargeted approach via computational MS to comprehensively characterize the whole soil microbial lipidome and evaluate the suite of potential lipid biomarkers associated with nitrogen cycling.

How to cite: Kerschhofer, F. P., Richter, N., Radujković, D., Verbruggen, E., Muñoz-Martín, M. A., Perona, E., Cantón Castilla, Y., Bauersachs, T., Ding, S., and De Jonge, C.: Intact polar lipids as biomarkers for nitrogen fixation and nitrification in European soils , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12957, https://doi.org/10.5194/egusphere-egu26-12957, 2026.

The Holocene temperature history of the lowland Amazon Basin remains poorly constrained, even though the region plays a key role in global climate, carbon cycling, and biodiversity. We present a Holocene record of glycerol dialkyl glycerol tetraethers (GDGTs) from a lake sediment core in the westernmost Amazon Basin, Bolivia, providing new constraints on regional temperature evolution and lake environmental conditions. The brGDGT based temperature reconstruction reveal a low amplitude, gradual warming trend throughout the Holocene. This pattern is consistent with other terrestrial records from tropical South America but contrasts with compiled tropical and global temperature reconstructions that suggest more pronounced early to mid-Holocene warmth followed by cooling. Our results therefore support the hypothesis that Holocene temperature evolution in tropical South America was distinct from that of other low latitude regions and from the global mean, highlighting the importance of regional climate dynamics and land surface feedbacks in shaping tropical climate trajectories.

In addition to temperature, GDGT distributions indicate four distinct phases of changing lake conditions over the Holocene, characterized by shifts in productivity and bottom water redox conditions. These variations likely reflect changes in local landscape development and catchment processes, as well as alterations in wind driven lake mixing. The most recent interval shows signatures consistent with enhanced productivity which may be linked to human activity in the catchment.

Together, these results provide new insights into the long-term temperature history of the western Amazon Basin and demonstrate the value of GDGTs for simultaneously reconstructing regional climate trends and lake environmental change in tropical lowland settings.

How to cite: Hällberg, P., Lombardo, U., Manzella, G., Schefuß, E., Stevens, T., and Peterse, F.: Holocene temperature and environmental reconstruction from Llanos de Moxos in western Amazon based on GDGTs, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20912, https://doi.org/10.5194/egusphere-egu26-20912, 2026.

Paleoclimatic and paleoenvironmental reconstructions rely on proxies derived from physical, chemical or biological properties of the investigated archive. In order to achieve the highest spatial (hundreds of micrometers), and thus temporal resolution (subannual), various imaging techniques, such as hyperspectral imaging, computed tomography, mass spectrometry imaging (MSI), X-ray, and µXRF can be employed. However, proxies generally respond to multiple environmental variables (e.g., the GDGT-based proxy CCat is influenced by both water column temperature and nutrient concentrations). Multi-proxy studies are necessary to obtain a comprehensive understanding of past conditions and to disentangle individual biogeochemical processes.

A major roadblock in multi-proxy studies is the alignment of data across multiple datasets since manual matching of ‘wiggles’ (1D time series) can be deceptive. With imaging data this issue can be avoided since data can be matched in 2D space. Moreover, RGB images are routinely obtained alongside each method. This provides a shared data layer between methods.

Not all imaging methods can be performed on the exact same sample slice, and MSI even requires multiple samples from the same core depth to cover multiple mass windows. Consequently, four aspects are taken into account in our proposed workflow: (I) subsamples need to be referenced back to the core; (II) datasets are obtained at different positions and can have vastly different resolutions; (III) samples may be distorted during sample preparation - so even two MSI measurements from the same sediment section at the same resolution cannot be mapped directly onto each other. And although these distortions are generally small, investigating seasonal variations requires consistency at the scale of hundreds of micrometers; (IV) after a transformation between images has been found, the data needs to be transformed (i.e., resampled). This requires interpolation, which can alter properties such as sparsity. Hence, interpolation targets as well as the interpolation methods need to be selected with care.

In this work, we present a workflow capable of semi-automatically combining image datasets from (sections of) sediment cores from any two imaging methods. Advanced methods for laminated sediments are also presented, as they are particularly suitable for fine-scale matching. With this workflow we aim to replace the tedious manual teaching point selection by providing robust image registration methods for routine multi-proxy studies on subannual scales.

How to cite: Zander, Y., Liu, W., Wörmer, L., and Hinrichs, K.-U.: A Workflow for Combining microscale Imaging Techniques in Paleoclimatology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11129, https://doi.org/10.5194/egusphere-egu26-11129, 2026.

Unlocking the functional complexity of soil ecosystems requires robust methods for characterizing the diverse communities residing within them. While phospholipid fatty acid (PLFA) analysis has long served as a standard tool for quantifying soil microbial community composition, it is inherently constrained by low taxonomic resolution and a historical bias toward bacteria and fungi, often obscuring the contributions of other critical soil organisms. To address this gap, intact polar lipid analysis offers potentially deeper and more detailed insight into the soil (micro)biome. Here, we present a comprehensive lipidomic reference library built from intact polar lipids extracted from pure isolates and individual species spanning the tree of life, including bacteria, archaea, fungi, protists, plants, and soil fauna to enable high-resolution, culture-independent biodiversity assessments.

Using reversed phase UPLC separation followed by dual-polarity, high-resolution Orbitrap MS/MS and molecular networking, we captured over 140,000 molecular features and organized them into approximately 10,000 molecular families. This library covers ~30 phyla and >50 lipid classes, extending the analytical window far beyond PLFA to include diverse glycerophospholipids, glycolipids, sphingolipids, and neutral lipids. Hierarchical analyses reveal distinctive lipidomic architectures across taxonomic levels, with over half of the detected compounds appearing exclusive to single phyla. Beyond standard microbial signals, we identified rich lipid fingerprints specific for faunal and protist groups (e.g., Arthropoda, Nematoda, Mollusca, Amoebozoa), plastid-associated glycolipids in photosynthetic lineages, and characteristic archaeal membrane compositions. Clustering these features yielded thousands of phylum-exclusive molecular families, providing candidate biomarkers with built-in signal redundancy.

As a proof-of-concept, we detected these signatures in heterogeneous soil samples, supporting the feasibility of the approach while highlighting the need for broader validation of potential biomarker families. These findings establish a path toward high-resolution lipid-based mapping of soil community composition and food-web structure, offering a powerful, functional complement to existing genomic and biochemical approaches.

How to cite: Samrat, R. and Wanek, W.: Beyond microbes: mapping soil food web biodiversity via lipid fingerprinting, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10003, https://doi.org/10.5194/egusphere-egu26-10003, 2026.