We seek studies that develop new lipid biomarkers and methods for applying biomarkers to modern settings and the geologic past in order to reconstruct environmental parameters such as temperature, precipitation, biogeochemical cycles, anthropogenic activities, and vegetation. These can be studies on the biosynthesis and phylogeny of source organisms, transport and diagenesis, calibrations to environmental parameters, proxy interpretation and applications to reconstruct past environmental conditions.
Changes in past East Asian monsoon (EAM) climate have been inferred from records of speleothem δ18O and the magnetic susceptibility (MagSus) of loess sequences on the Chinese Loess Plateau (CLP). However, where the speleothem record is dominated by a 23-kyr cycle, loess MagSus primarily shows a 100-kyr cycle. Generating a long-term high-resolution record of plant wax hydrogen isotopes (δ2Hwax) from the Yuanbao section on the western CLP reveals that variations in δ2Hwax follow the precessional pattern of the speleothem record, as opposed to the glacial-interglacial changes in MagSus from the same loess section. We, therefore, propose that plant waxes mainly record the δ2H of precipitation during the growing season, whereas MagSus represents an annual climate signal, including precipitation and temperature. This implies that summer vs annual climate variability is driven by distinct orbital forcings.
Regardless, these proxies only allow for qualitative reconstructions of past EAM climate; a method to generate records of absolute monsoon precipitation changes and also leads to consistent results across the CLP is still lacking. We find that in the Yuanbao section, the degree of cyclisation (DC) of branched tetraether membrane lipids, so-called brGDGTs, which are membrane lipids of soil bacteria that are mostly known for their temperature-sensitivity, closely tracks the changes in δ2Hwax. The positive relationship of the DC with mean annual precipitation (MAP) in surface soils from the CLP enables us to quantify past MAP at Yuanbao, but also at other sites on the CLP with existing brGDGT datasets. This reveals a spatial gradient in MAP that is most pronounced during glacials, when the western CLP experiences relatively more arid conditions. Furthermore, the DC records provide independent support for precession as main forcing of precipitation on the CLP, as opposed to the 100-kyr cycle recorded by MagSus, which rather reflects the relative intensity of the EAM.
How to cite: Peterse, F., Fuchs, L., Lu, H., Ziegler, M., and Sun, Y.: Towards quantitative reconstruction of past East Asian monsoon precipitation based on lipid biomarkers in Chinese loess, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2788, https://doi.org/10.5194/egusphere-egu25-2788, 2025.
Understanding human adaptations to high altitude contexts, and the impact of climatic change and associated vegetation change on human societies is a key research theme in archaeological, palaeoecological, and palaeoanthropological research. In many highland regions, variations in temperature related to elevation and aspect are associated with the distribution of plants following the C3 and C4 photosynthetic pathways. In Lesotho, δ13C of soil organic matter and faunal material is commonly used in archaeological research to infer palaeoenvironmental change and its connection to changes in human behavioural and settlement patterns. However, there is limited modern reference information for δ13C in the region with which to interpret past dynamics.
We present the results of bulk δ13C and compound-specific isotope analysis (CSIA; δ13C and δ2H) of long-chain n-alkanes from modern soil samples collected from four elevation transects covering 1,800 to 3,300 m a.s.l. in eastern Lesotho, from both north- and south-facing slopes. Consistent with modern ecological observations, elevation, and, in turn, temperature, are major controls on the distribution of C3 and C4 vegetation along the transects. Bulk sediment and n-alkane (C29, C31 and C33) δ13C results from north-facing slopes track the transition from C4 dominated to C3 dominated vegetation with increasing elevation, although this transition point varies by n-alkane chain-length. On south-facing slopes, which receive less solar radiation, CSIA δ13C values largely reflect C3 dominated vegetation, including at lower elevations than on the north-facing slopes. Differences observed between the bulk sediment and CSIA δ13C results are likely related to the impact of microbial activity in the bulk sediment samples, and highlight the advantages of compound specific analysis in identifying and exploring these discrepancies.
Variability in δ2H along the transects is less distinct, but also observed, particularly between north- and south-facing slopes. Mean δ2H values between north- and south-facing slopes are offset by up to 30 ‰. The results of this study provide a reference baseline for studying past ecological change in this region, where the application of compound specific isotope analysis of sediments from archaeological sites is increasingly used to improve our understanding of past human-environment interactions in highland areas.
How to cite: Rudd, R., Patalano, R., Jha, D. K., van Schalkwyk, J., van Schalkwyk, L., Mokhachane, R., Stewart, B. A., and Roberts, P.: Plant wax n-alkanes track C3-C4 vegetation transitions and hydrological responses along elevation gradients in Lesotho, southern Africa , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17244, https://doi.org/10.5194/egusphere-egu25-17244, 2025.
Lake sediment provides information on hydrogeological and environmental conditions. It contains a wide range of physical, chemical, and biological archives that could be used to reconstruct paleoclimatic trends and shifts. Applying lipid biomarker proxies to lake sediment is widely used to reconstruct past conditions. However, it is also essential to consider the stages of lake evolution. In particular, a lake that is surrounded by steep slope topography potentially has a mix of watershed and water body organic material sources. In this study, we aim to disentangle terrestrial and aquatic organic matter sources using a range of lipid biomarker proxies.
Shenmihu Lake is located in the mountains near Yilan, northeastern Taiwan, about 1000 meters above sea level, and surrounded by steep slopes and ephemeral creeks containing loose gravel that may be transported to the lake by rain or extreme weather (torrential rain, typhoon, etc.). A 9,78m long composite core was retrieved from the lake using a Russian corer, and sub-samples were taken every 20 cm from the core. The bottom part of the core was radiocarbon dated to about 10700 BP, and the age model suggests continuous sedimentation spanning the entire Holocene. The Carbon Preference Index (CPI) and Paq ratio can be used to distinguish organic material sources from terrestrial, emergent, or submerged macrophytes. The preliminary result showed that organic materials of around 8000 and 6700 BP were dominated by floating macrophytes, indicating that water fully covered the lake. A better understanding of lake succession and lake internal processes is necessary to allow extracted paleoenvironmental archives to be compared to regional and global climate records.
Keywords: Lipid biomarker, lake sediment, Russian core, Asian monsoon
How to cite: Setiaji, R. A., Löwemark, L., Ho, S. L., and Huang, K. F.: Climate driven Holocene variations in lipid biomarkers from Shenmihu Lake, Northeastern Taiwan, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14005, https://doi.org/10.5194/egusphere-egu25-14005, 2025.
The stable isotopic composition of plant waxes (δ13C and δ2H values) in lake sediments is a powerful tool for reconstructing past climates and environments, offering critical insights into hydroclimate variability and vegetation dynamics. Different plant types, such as grasses and woody vegetation, can exhibit distinct water sources and isotopic fractionations, directly influencing plant-wax isotopic signatures in sedimentary records. This influence is particularly pronounced in small basins, where local vegetation sources can dominate over regional signals, complicating the interpretation of δ2H records. Disentangling the effects of vegetation changes from hydroclimate variations in lipid biomarkers is paramount for robust interpretations yet remains quite challenging.
Here, we aim to quantify the effects of climate, vegetation, and human activities on sedimentary records, improving our understanding of environmental changes in central Switzerland. We utilized δ13C and δ2H records of plant waxes (n-alkanes and fatty acids) from Rotsee, a small lake near Luzern. Our Bayesian-based 14C age model establishes a temporal framework for interpreting changes in vegetation and hydroclimate at Rotsee since the Younger Dryas period (12.9–11.7 ka). The extensive paleoclimate and archaeological research in the region offers a complementary and broader context for our findings.
During the Younger Dryas, leaf wax δ13C and δ2H values were very low — consistent with cold and dry conditions. δ2H values of long-chain fatty acids increase rapidly during the transition to the Early Holocene, in what appears to be a double-step change: an initial ~20 ‰ increase driven by hydroclimate changes (δ13C remained stable) followed by ~30 ‰ driven by changes in regional vegetation (accompanied by a ~10‰ δ13C increase). This overall ~50 ‰ increase in δ2H aligns with a major and well-known regional warming trend.
During the Holocene Thermal Maximum, around 9.5 to 6 ka, δ13C values peaked, likely reflecting the dominance of woody plants and increased input of aquatic plants, while δ²H values remained stable. However, after 6 ka, there were significant shifts in δ¹³C values, possibly reflecting local vegetation source changes at Rotsee such as a decrease in aquatic plants.
Around 2 ka, during the Roman Period, the plant wax isotopic records at Rotsee show a major shift, with δ2H values declining by ~40‰ and δ13C by ~5‰ in long-chain fatty acids. This substantial change in δ2H values exceeds what would be expected based on plausible hydroclimate variations during this period, suggesting a vegetation source-driven change. The intensification of forest clearance and cereal cultivation, as indicated by pollen records, suggests that human-driven land use changes likely strongly influenced the δ2H signal. After medieval times (ca. 0.5 ka), plant wax δ13C and δ2H values increased significantly, likely due to forest regrowth and Rotsee’s eutrophication.
Overall, this study highlights the potential of plant-wax isotopes to reveal complex interactions among climate, vegetation, and human activity. Our findings demonstrate how sedimentary records from small basins similar to Rotsee can provide valuable insights into local and regional environmental dynamics.
How to cite: N. Santos, R., Klatt, A., B. Nelson, D., Ajallooeian, F., Schubert, C., Dubois, N., De Jonge, C., and Ladd, S. N.: Disentangling the impact of vegetation and hydroclimate dynamics on plant wax stable isotopes since the Younger Dryas in Central Switzerland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8560, https://doi.org/10.5194/egusphere-egu25-8560, 2025.
Biomarkers are biological remnants of extinct species which are generally found in sediments. The preserved molecular structures provide crucial insights into the organic matter's origin and precursor materials and serve as valuable proxies for reconstructing the ancient sedimentary environment. These biomarker serve as "molecular fossils" that offer important clues about past environments and life. This paper presents a detailed biomarker study of the organic-rich shales from open cast coal mines of Pranhita-Godavari (P-G) valley in South Central India. The Gondwana Basins of India, including the PG, are the primary coal producing regions, contributing approximately 98-99% of the nation's total coal reserves. The Barakar and Lower Kamthi Formations of the PG basin host significant reserves of power-grade coal. The shales collected from three sub-basins, namely Godavari in northern, Kothagudem and Chintalpudi sub-basin in southern part of PG. The presence of n-alkanes in the range of n-C12 to n-C35, along with acyclic isoprenoids i.e. pristane and phytane in majority of samples indicates that the organic matter was derived from terrestrial higher plant sources deposited in a reducing environment, except for a few. The Pr/n-C17 versus Ph/n-C18 ratios indicate that the P-G samples predominantly contain terrigenous type III kerogen with a minor contribution from mixed type II & III kerogen. Important polycyclic aromatic hydrocarbons (PAH) such as naphthalene, phenanthrene, and their alkylated derivatives, dibenzothiophene were also observed in the samples of P-G Valley. The DBT/P ratio from several shales is high to very high (>2), indicating the marine contribution during the sediment deposition. The other important PAH identified are the pyrene, benzo[a] anthracene, fluoranthene, and benzo[a] pyrene are found in the aromatic fraction of PG shale. These aromatic biomarkers have the potential to provide better understand the origin, depositional environment, thermal maturity, and potential for hydrocarbon generation of coal deposits. The P-G Basin shalse, characterized by excellent organic richness and thermal maturity, exhibits a complex origin, reflecting contributions from both terrestrial and aquatic organic matter sources. Furthermore, the depositional environment in this basin witnessed a significant transition, shifting from marine/aquatic to terrestrial conditions during the Permian period.
How to cite: Prusty, D., Mani, D., Bhattacharyya, S., Konar, R., Das, K., Srinivas J, S., Kaduru, R., and Nadeem, A.: Molecular geochemistry study of carbonaceous shale from Pranhita-Godavari valley, India: Implication for source rock properties, depositional environment and thermal maturity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20766, https://doi.org/10.5194/egusphere-egu25-20766, 2025.
The TEX86 proxy, based on archaeal isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs), is among the most widely used tools for reconstructing past sea surface temperatures (SST). However, the impact of water depth on isoGDGT distributions and the reliability of TEX86 remains unclear. To address this, sediments from five hadal trench regions and a comprehensive global dataset were analyzed. The findings reveal that as water depth increases, the fractional abundance of low-ring-number isoGDGTs (e.g., GDGT-1 and GDGT-2) increases, while that of high-ring-number isoGDGTs (e.g., GDGT-3 and crenarchaeol) decreases. Notably, the crenarchaeol regio-isomer, despite its high-ring structure, display an unusually higher fractional abundance in deep-sea sediments, suggesting a distinct source or history compared to other isoGDGTs. Despite the influence of water depth, isoGDGT compositions and TEX86 maintain strong correlations with SSTs across varying depths, including the deepest oceanic regions, indicating the dominance of shallow-water-derived signals in sedimentary isoGDGT pools. The influence of water depth on TEX86 is even more minimal, likely due to compensatory changes in GDGT-2 and GDGT-3 and the proxy’s inherent ratio structure. Remarkably, TEX86 provides more reliable SST estimations in deep-sea sediments compared to coastal sediments. By excluding the crenarchaeol regio-isomer from TEX86, the resulting proxy demonstrates a stronger correlation with SSTs, reduced sensitivity to water depth, and improved performance in polar regions. Consequently, newly TEX86-SST calibration models were established to enhance SST estimations globally and across regions with varying water depths.
How to cite: Xiao, W., Zhang, C., Xu, Y., Zheng, F., Frank, W., and Glud, R.: Assessing Water Depth Effects on Archaeal Lipids and Refining the TEX86 Proxy: Insights from Hadal Trenches to a Global Scale, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19275, https://doi.org/10.5194/egusphere-egu25-19275, 2025.
Hydroxylated isoprenoid glycerol dialkyl glycerol tetraethers (OH-GDGTs) are ubiquitous, degradation-resistant archaeal membrane lipids. In marine environments, they are primarily thought to be produced by ammonia-oxidizing archaea Nitrososphaeria, and previous studies have shown that the number of cyclopentane moieties is positively correlated with upper ocean temperatures. This relationship has led to the development of the RI-OH and RI-OH’ paleothermometers. However, the low abundance of OH-GDGTs in marine settings, particularly in low-latitude regions, makes OH-GDGT-based paleothermometers relatively susceptible to the contribution of other archaea groups, such as methane-cycling benthic archaea, to the sedimentary OH-GDGT pool. This can potentially bias the relationship between the number of cyclopentane moieties and upper ocean temperatures.
Until now, the potential influence of OH-GDGT production by anaerobic methanotrophic archaea has remained unexplored. To address this gap, we studied four sediment cores collected using a remotely operated vehicle within a ~200 m radius at three sites in the Four Way Closure Ridge cold seep system, offshore southwestern Taiwan. Three cores were collected from black patches associated with active seepage, while one control core represented a "normal" marine setting unaffected by seepage. A suite of data, including gas, porewater, bulk sediment geochemistry, archaeal genomics, and GDGT distributions, was generated.
We tested various calibrations using the control core, and found that the latest global RI-OH calibration yields temperatures that agree with the annual mean sea surface temperatures (SST). In contrast, other RI-OH and RI-OH’ calibrations produce temperatures that skew toward the summer and winter months, respectively. In three other sediment cores affected by anaerobic methanotrophic archaea, we observed that the Methane Index, which estimates the contribution of anaerobic methanotrophic archaea to the isoprenoid GDGT pool, reached as high as 0.7. Furthermore, we observed that when Methane Index values increase, the relative abundance of OH-GDGT-1 tends to increase as well, while that of OH-GDGT-2 tends to decrease. These changes corresponds to a temperature decrease of up to ~4°C as reconstructed using the RI-OH paleothermometer, while only marginally impacting the RI-OH' paleothermometer and the isoprenoid GDGT-based TEX86 (< 1°C). These findings suggest that anaerobic methanotrophic archaea may contribute to the sedimentary OH-GDGT pool in addition to the isoGDGT pool, potentially introducing a previously unidentified cold bias in the RI-OH paleothermometer. This underscores the need for further investigations into the role of anaerobic methanotrophic archaea in OH-GDGT production to improve the accuracy of RI-OH-based temperature reconstructions.
How to cite: Fenies, P., Ho, S. L., and Jens, H.: Uncovering a potential bias in the RI-OH paleothermometer in methane seepage environments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-785, https://doi.org/10.5194/egusphere-egu25-785, 2025.
Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are membrane lipids produced by bacteria in soils and peats worldwide. The distribution of brGDGTs relates to ambient environmental conditions, and the changes in their downcore distributions preserved in coastal marine sediments are used to reconstruct past temperatures of adjacent river catchments. However, brGDGT signatures in lakes and rivers deviating from those in soils suggest in situ production of brGDGTs, which can alter the original soil signal. In this study, we incubated river water with and without soils with 13C-labeled glucose addition to identify characteristics of brGDGTs produced in situ. We observe that the brGDGT signature shifts from more 5-methyl to more 6-methyl brGDGTs in river water, while the river water with soil remains dominated by 5-methyl brGDGTs during the incubation. Furthermore, the 6-methyl brGDGTs in river water show an uptake of 13C-labeled glucose added to the experiment, providing direct evidence of their production in an aquatic environment. However, label uptake by brGDGTs in experiments with soil addition was minimal, suggesting that brGDGTs produced in aquatic environments only alter the initial soil-derived brGDGT signal at times when soil input is relatively low.
How to cite: Guo, J., Eefting, D., Nierop, K., Middelburg, J., and Peterse, F.: Direct Evidence of 6-methyl Branched Tetraether Production in Freshwater, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3554, https://doi.org/10.5194/egusphere-egu25-3554, 2025.
The loess-paleosol sequences of the Khovaling Loess Plateau in southern Tajikistan preserve a unique record of early hominin occupation and environmental changes during the Early Pleistocene (Marine Isotope Stages 11–15). Using a combination of biomarkers, stable isotopes, and magnetic susceptibility analyses, our research reconstructs paleoenvironmental and fire histories while investigating the impact of early humans on the landscape. Biomarker proxies, including straight-chain alkanes (n-alkanes) and polycyclic aromatic hydrocarbons (PAHs), reveal shifts between grass-dominated and forested ecosystems corresponding to glacial and interglacial cycles respectively. The enrichment of high molecular weight PAHs in stratigraphic layers with lithic artifacts suggests anthropogenic fire use during periods of wetter climates. The complementary stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes together with soil organic matter contents indicate intensive human activity in on-site contexts, with a reliance on C3 vegetation under cooler, wetter conditions. Off-site and near-site locales exhibit isotopic signatures reflecting less intensive human use and more open landscapes dominated by grassier vegetation.
The integration of these geochemical and isotopic proxies highlights the potential of soils and sediments to offer insights into the interplay between environmental changes and human activity. By linking these molecular findings with lithic artifact distributions and magnetic susceptibility records, our study demonstrates how loess soils preserve evidence of early human adaptation, resource use, and ecological impacts, contributing to our understanding of co-evolutionary relationships between hominins and landscapes in Central Asia.
How to cite: Chirakkal, A., K Wright, D., Kulakova, E., Constantin Stiendal, C., Jonathan Birk, J., Kurbanov, R., and Buylaert, J.-P.: Biomarkers and Stable Isotopes in Loess Deposits Reveal Early Human-Environment Interactions in Central Asia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4978, https://doi.org/10.5194/egusphere-egu25-4978, 2025.
Comprehensive organic geochemical analyses were conducted on 41 light crude oil samples obtained from diverse structural zones within the Xihu Depression. These analyses revealed a pronounced enrichment of biomarkers, highlighting substantial contributions from terrestrial higher plants. Notably, tricyclic diterpanes and their aromatized derivatives were identified as key molecular markers, primarily derived from angiosperms, gymnosperms, and ferns. In contrast, biomarkers indicative of inputs from aquatic lower plants were significantly less abundant.
Detailed geochemical profiling uncovered distinct spatial variations in biomarker composition across the structural zones, as evidenced by diagnostic ratios such as isopimarane/nC20, isopimarane/(isopimarane + 16β(H) phyllocladane), 1,2,5-trimethylnaphthalene/1,3,6-trimethylnaphthalene, and 1,7-dimethylphenanthrene/(retene + 1,7-dimethylphenanthrene). These compositional variations, analyzed through multivariate statistical techniques, facilitated the classification of the crude oils into four distinct groups, reflecting variable contributions from angiosperms, gymnosperms, and ferns.
Furthermore, the study established a robust linkage between the saturated and aromatic hydrocarbon fractions of the crude oils, using high-resolution gas chromatography-mass spectrometry (GC-MS) to investigate their molecular signatures. A novel biomarker-based index, defined as (isopimarane + 1,7-dimethylphenanthrene)/(retene + 16β(H) phyllocladane), was developed to infer the source input of the light crude oils. Elevated values of this index were interpreted as indicative of a dominant gymnosperm-derived input. Notably, a positive correlation was observed between this index and the bulk δ13C values of the crude oils, further corroborating the critical role of gymnosperm resins in the hydrocarbon generation processes within the Xihu Depression. This integrated geochemical framework provides valuable insights into the source contributions and depositional settings of the region's petroleum systems.
How to cite: Jiang, Y. and Cheng, X.: Environmental and Botanical Insights from Biomarker Variability in Xihu Depression Light Crude Oils, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7916, https://doi.org/10.5194/egusphere-egu25-7916, 2025.
Throughout recent decades, cultural eutrophication has threatened freshwater ecosystem functioning. However, anthropogenic activity has also heavily impacted aquatic environments earlier in human history. During the 2nd century BCE Aventicum (capital of the Roman province Helvetica), located at the southern border of Murtensee, was inhabited by ~20,000 people. This led to significant disturbances of the lake and its environment, which persisted for centuries, including increased soil erosion, cultural eutrophication, and major changes of the local vegetation. Here, we aim to investigate algal population dynamics in Murtensee in response to this known anthropogenic forcing during the Roman Period, by combining organic geochemical proxies with sedimentary ancient DNA (sedaDNA) analyses.
To analyse the effects on the algal community, a 15-meter-long sediment core, spanning > 8 kyr, was collected in April 2023. We present a record of the relative abundance of lipid biomarkers, which we used to reconstruct the ratio between eukaryotic algae and cyanobacteria and to provide insights about the diversity among eukaryotes. Our results reveal a prominent shift towards cyanobacteria during the Roman period, and a substantial decrease of specific phytosterols indicative of dinoflagellates and diatoms. We complement our analyses of biomarker distributions with compound-specific hydrogen isotope measurements of fatty acids, n-alkanols, and phytol, and use the offsets among these to further distinguish ecological changes in the lake. In addition to our organic geochemical data, we analysed sedaDNA using a metabarcoding approach targeting cyanobacteria. The results of these analyses indicate an increase in cyanobacterial diversity associated with the Roman eutrophication.
We analysed not only the immediate effects of Roman activities on the algal community but also investigated the long-term consequences of this disturbance over the following centuries. Although human pressure was reduced following the Roman period, the effect on the algal community composition was long-lasting, with persistent reduced diatom abundance for at least three centuries, and reduced dinoflagellate presence for over 1.5 kyr.
Our research emphasizes that even while ancient human activity was less pronounced compared to modern perturbations, it had a significant and persistent effect on the algal community. This suggests that centuries to millennia may be required for ecological recovery in the aftermath of a eutrophication disturbance.
How to cite: Wietelmann, T., Epp, L., Dubois, N., N. Santos, R., Nelson, D. B., and Ladd, S. N.: Persistent effect of ancient Romans on algal community in Murtensee (Switzerland), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8285, https://doi.org/10.5194/egusphere-egu25-8285, 2025.
Due to their response to environmental parameters and global distribution, the bacterial and archaeal lipids Glycerol Dialkyl Glycerol Tetraethers (GDGTs) have been used as proxies for environmental studies in marine and terrestrial settings for the past decades. Since these molecules were first discovered, improvements in the analytical method have been made, from the initial method that allowed for the identification of these compounds using cyanocolumns run in an HPLC-MS system, to the separation of their different isomers using two silica columns in series. While currently the most widely used method, using the silica columns, has been shown to produce very reproducible results across different laboratories, the runtime of the program of approximately 90 minutes makes it burdensome to analyze large arrays of samples, and the long runtime also requires large volumes of solvent. These are significant limitations for the application of this analysis in paleoclimate studies where large numbers of samples are required. Furthermore, since this method is run in Single Ion Monitoring mode, other related compounds are not currently being analyzed along the GDGTs.
Here we present the initial results of implementing a Supercritical Fluid Chromatography coupled to quadrupole Time of Flight mass spectrometry (SFC-qTOF) system to measure GDGTs. We report that this method produces results with comparable distribution of the GDGTs to the classical HPLC-MS method, where the GDGTs are correctly detected although no isomer separation is observed. Nevertheless, our total runtime is 25 minutes and also uses less than a third of the solvent from the standard method, as it primarily uses supercritical CO2 as mobile phase, supplemented with no more than 40% of methanol:ethanol (1:1). Furthermore, while other alternative techniques, such as reverse phase chromatography have also reduced the runtime of the GDGT analysis, since our system is running in normal phase, our results are easily comparable with those of the commonly made analyses. The implementation of a faster analysis would allow for an easier application of GDGT analyses to high resolution paleoreconstruction analyses.
While improvements in this method are still required, the versatility of the SFC-qTOF system, as demonstrated in its use for lipidomic studies, could provide a useful tool to not only measure the commonly studied GDGTs, but also by expanding the analysis to less studied structures such as intact polar lipids and unidentified GDGTs. Previous work has shown that the measurement of additional non-traditional GDGTs can provide extra paleoecological information, thus allowing for more robust and reliable paleoreconstructions.
How to cite: Martínez-Sosa, P., Touboul, D., Bourcier, S., and Huguet, A.: Application of a Supercritical Fluid Chromatography quadrupole Time of Flight system to the detection of Glycerol Dialkyl Glycerol Tetraethers , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9764, https://doi.org/10.5194/egusphere-egu25-9764, 2025.
Estimates of sea surface temperature (SST) in the geologic past often rely on geochemical proxies, including alkenone unsaturation ratios (UK’37), the proportion of cyclopentane rings in glycerol dibiphytanyl glycerol tetraethers (GDGTs; TEX86), δ18O and Mg/Ca in planktonic foraminifera, and clumped isotopes in biogenic carbonates (Δ47). Global calibrations show robust agreements between proxies and the temperature of the environment. However, proxy values in the eastern Mediterranean Sea are often offset from expected values based on these global relationships.
Here we aim to explain the Meditrerranean Sea proxy bias using sediment traps moored in the water column at 500, 1500, and 2500 m depth in the Ionian Sea between 1999 and 2018. We compare proxy values in trap material to those in surface sediment from the same site. UK’37-based SSTs (~12-22 °C) and TEX86-based SSTs (~28-30 °C) vary seasonally, although they differ from satellite-based SSTs (~16-27 °C). No significant variations in mean Mg/Ca or δ18O values in G. ruber or in coccolith Δ47 values were observed, indicating that these proxies do not vary on seasonal timescales in sinking particles at this site. Ultimately, however, sediments should record a flux-averaged proxy value. To this end, we explore export patterns of biomarkers and foraminifera.
We find that export of alkenones, GDGTs, and foraminifera exhibit different seasonality. Specifically, alkenone export typically peaks twice per year in late winter and late summer, maximum GDGT export often occurs in late winter, and export of planktonic foraminifera generally peaks in summer. Furthermore, alkenone export exhibits very little inter-annual variability, whereas the timing of GDGT export is more variable, and the peak flux of foraminifera is highly variable between years.
Flux-weighted UK’37- and TEX86-, and mean coccolith Δ47-based SSTs of 15, 29, and 15 ± 2 °C, respectively are offset from mean annual average satellite-based SSTs of 21 °C, whereas Mg/Ca and δ18O of G. ruber both yield average temperatures that are similar to the satellite-derived SSTs. Notably, whereas most proxy values measured in the surface sediment closely reflect those in the sediment trap material, the UK’37-based SST (13 °C) differs from the flux-weighted average in the sediment trap.
These results will be discussed in the context of seasonality, nutrient availability, dwelling depth, ecology, and physiological processes which may influence proxy values measured in the sediment trap and in underlying sediments.
How to cite: Rice, A., van Boxtel, A., de Lange, G. J., Stuut, J.-B., Reichart, G.-J., de Nooijer, L., Bernasconi, S., Stoll, H., Sluijs, A., Ziegler, M., and Peterse, F.: Organic, inorganic, and isotopic proxy temperature estimates from a ten-year sediment trap record in the eastern Mediterranean Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9876, https://doi.org/10.5194/egusphere-egu25-9876, 2025.
The molecular and isotopic analysis of leaf wax biomarkers in sedimentary records is a widely used tool in palaeoclimate and palaeoenvironmental research. These biomarkers, particularly n-alkanes, are valued for their molecular stability, water insolubility, and resistance to microbial degradation, making them key indicators for reconstructing ancient environmental conditions. Despite extensive research on leaf wax n-alkanes in lacustrine, fluvial, and marine environments, their application in desert ecosystems remains limited [1]. This study analyses n-alkane distributions and their compound-specific isotopic signatures (CSIA; δ¹³C and δ²H values) in modern plants and sediments across an east-west aridity gradient of the Thar Desert.
Distinct patterns in n-alkane concentrations (∑Alk; C25-C33), Carbon Preference Index (CPI), and Average Chain Length (ACL) were observed across plants and sediments, revealing their relationship with climatic parameters. Inter-species variability in the abundance of C29 and C31 is observed, but when averaged to C3 and C4 photosynthetic groups we see a C31 chain dominance in both plants. Meanwhile, average ∑Alk of sediments indicated C29 dominance. C3 plants had the highest ∑Alk and TOC (%), followed by C4 plants, with sediments showing significantly lower ∑Alk due to microbial degradation. CPI and ACL values distinguished these groups, with C4 plants showing the highest values, reflecting their physiological adaptations to arid environments through increased odd-chain alkane production to minimise water loss.
Pearson correlation analyses revealed strong relationships between ∑Alk in C4 plants and climatic parameters, with positive correlations with Mean Annual Temperature (MAT) and negative correlations with Mean Annual Precipitation (MAP) and Aridity Index (AI). These relationships highlight the superior water-use efficiency of C4 plants compared to C3 plants, enabling their dominance in semi-arid and arid regions. However, the ACL and CPI values of both plant types and sediments showed limited correlation with environmental variables, except for a strong correlation between the ACL of C4 plants and AI.
Our preliminary statistical analysis using ANOVA and Tukey's HSD test suggests a significant difference in the δ¹³C values of n-alkanes (C29 and C31) between C4 plants and sediments, while the bulk δ¹³C values are similar for both. This similarity indicates a bias of bulk δ¹³C values toward the C4 signature in sediments of the Thar Desert, highlighting the need for caution when reconstructing historical climate and vegetation changes. This finding aligns with other research that has documented similar biases in bulk δ¹³C values during palaeoenvironmental reconstructions. Furthermore, the bulk δ¹³C values of plants and sediments are more sensitive to MAT, MAP, and AI compared to the δ¹³C values of n-alkanes (C29 and C31) in this region. These findings also provide valuable insights into plant responses and their organic matter preservation potential in arid ecosystems.
Referenc:
[1] Jha, D.K., Patalano, R., Ilgner, J., Achyuthan, H., Alsharekh, A.M., Armitage, S., Blinkhorn, J., Boivin, N., Breeze, P.S., Devra, R., Drake, N., Groucutt, H.S., Guagnin, M., Roberts, P., Petraglia, M.D. 2024. Preservation of plant‐wax biomarkers in deserts: implications for Quaternary environment and human evolutionary studies. Journal of Quaternary Science, 39 (3), pp.349-358.
How to cite: Jha, D. K., Miyash, N., Gupta, P., Rudd, R., Singh, S. P., and Roberts, P.: Plant Biomarkers in Arid Ecosystems: Molecular and Isotopic Insights from the Thar Desert, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10135, https://doi.org/10.5194/egusphere-egu25-10135, 2025.
Arctic sea ice plays a crucial role in regulating the Earth’s energy budget, influencing Arctic marine productivity, and the global thermohaline circulation. Its distribution also affects the transport of sediment and organic matter (OM) across the Arctic Ocean. Lipid biomarkers are essential proxies for tracing OM transport in the central Arctic. However, their sources and patterns of spatial and temporal variability during the last glacial cycle remain poorly understood. To address these knowledge gaps, our study conducted a multiproxy analysis—including total organic carbon (TOC), n-alkanes, and glycerol dialkyl glycerol tetraethers (GDGTs) on nine sediment cores from the central Arctic. The GDGT record suggests that branched GDGTs (brGDGTs) in the central Arctic are predominantly of marine origin, challenging the previously held assumption of a terrigenous source. To determine the origin of brGDGTs in this region, two indices were applied, yielding contrasting results. Elevated IIIa/IIa values during MIS 3–1 indicate a marine source, whereas #ringstetra ratios point to a terrestrial origin. However, the reliability of #ringstetra ratios in the central Arctic is likely compromised due to their sensitivity to pH variations, making the IIIa/IIa ratio a more reliable indicator of in situ brGDGT production in the region. TOC, along with terrestrial biomarkers (long-chain n-alkanes) and marine biomarkers (isoprenoid and branched GDGTs), showed the highest concentrations in the Central Lomonosov Ridge (CLR) cores, located closer to the Siberian shelves. These concentrations decreased in Lomonosov Ridge Offshore (LRG) and Morris Jesup Rise (MJR) cores, further from the shelves. This spatial pattern, combined with evidence of low productivity in the central Arctic, suggests that both marine- and terrestrial-derived biomarkers were primarily transported via sea ice drift from the Siberian shelves. This transport process persisted through MIS 3–1, albeit with reduced intensity during glacial periods. Moreover, elevated Branched Isoprenoid Tetraether (BIT) index values in the central Arctic during glacial periods likely reflect changes in crenarchaeol and brGDGT production on the shelves and/or the selective degradation of crenarchaeol during transport.
How to cite: Singh, A., Löwemark, L., Ho, S. L., Chen, M.-T., Wang, P.-L., Jakobsson, M., and Gyllencreutz, R.: Distribution patterns of GDGTs and n-alkanes in the central Arctic Ocean during Marine Isotope Stages 1, 2, and 3, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11308, https://doi.org/10.5194/egusphere-egu25-11308, 2025.
Bacteriohopanepolyols (BHPs) are structurally diverse compounds produced by a wide range of bacteria making them ideal candidates as chemotaxonomic biomarkers and indicators of bacterially driven biogeochemical processes in the geological record. In this study, we characterize changes in the BHP distribution in the Black Sea over the past 20 ka as the basin underwent three distinct environmental phases: (i) an oxic lacustrine phase where the Black Sea was disconnected from the global ocean; (ii) a transition period marked by the initial influx of marine water into the basin; and (iii) a marine phase where the basin was permanently euxinic, i.e. the bottom water is characterized by sulfidic conditions and a lack of oxygen. During the lacustrine phase we observe a high abundance and diversity of nucleoside BHPs (Nu-BHPs) that are likely associated with high terrigenous inputs. We also find evidence of BHPs likely associated with the nitrogen-cycle. For instance, an increase in oxazinone-aminobacteriohopanetriol could indicate that there was enhanced nitrite-oxidation during the lacustrine phase. The transition phase is generally characterized by an increase in the abundance of methoxylated-BHPs and various BHPs that are generally associated with aquatic environments (e.g., aminobacteriohopanetriol). Methoxylated-BHPs also persist into the marine phase, indicating that these BHPs may be specific to saline environments. The euxinic marine phase (7.2 ka-present) is composed of two stages. The early stage is characterized by a high abundance of aminobacteriohopanetetrol and aminobacteriohopanepentol, as well as ethenolamine-bacteriohopanepentol and -bacteriohopanehexol, that are likely transported to the sediments from the shallow oxycline niche of their methanotrophic sources. The later marine phase is characterized by a decline in these BHPs, likely due to a deepening of the oxycline. The change in distribution of many BHPs throughout the record may either be attributed to microbial adaptations to significant shifts in the oxygenation and/or hydrology of the basin or are associated with specific groups of bacteria that are suited to these environmental conditions. Throughout the record, diagenetic products of BHPs (e.g., anhydrous-bacteriohopanetetrol) were detected. These BHPs, however, remain a small proportion of the overall BHP composition, indicating high preservation conditions throughout the record. This study offers new insights into changes in microbial communities and biogeochemical processes that occurred in the Black Sea during the Last Deglaciation and Holocene in response to significant shifts in the hydrology and oxygenation of the basin.
How to cite: Richter, N., Cutmore, A., Bale, N., Schouten, S., and Rush, D.: Bacteriohopanepolyols track environmental transitions in the Black Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11517, https://doi.org/10.5194/egusphere-egu25-11517, 2025.
Leaf wax hydrogen isotopic composition (δDwax) is increasingly used to reconstruct precipitation variability over geological time scales. A significant advantage of δDwax analysis compared to isotopic proxies from speleothems or ice cores is that the isotopic composition of a range of n-alkanes sourced from algae, aquatic plants and terrestrial plants is measured simultaneously. This additional data allows for investigations of multiple aspects of the hydrological cycle such as dry season evapotranspiration and seasonal distribution of rainfall. However, uncertainties persist in interpreting the δD of different n-alkanes, and as a result, δDwax studies often focus on a single terrestrial n-alkane (C27, C29, or C31). The choice of n-alkane can significantly influence the reconstructed precipitation record, potentially leading to divergent interpretations. Moreover, only a subset of the available data is typically utilized, suggesting that leaf wax analyses may hold untapped potential for deeper insights.
In this ongoing study, we explore the n-alkane distribution and hydrogen and carbon (δ13Cwax) isotopic composition from an 18 000-year-long lake core in Thailand. High-resolution radiocarbon dating (n=65) was used to construct a well-constrained age model for the deglaciation. Our results indicate that δDwax records intense wetting during the Bølling and Older Dryas periods (~14.7-13.9 ka BP). Interestingly, δ13Cwax reveals a simultaneous shift toward dry-adapted C4 plants, suggesting seasonally dry conditions that impact vegetation, while δDwax likely reflects a wet-season signal. Allerød (13.9-12.8 ka BP) is marked by drying coinciding with a shift back to wet-adapted C3 vegetation. δDwax thereby appears to be seasonally biased in this tropical lake, at least for the deglacial period. The hydroclimate response during the Younger Dryas cold period (12.8-11.7 ka BP) is ambiguous based on different n-alkanes in our δDwax record – and even sign of change varies for the C25 to C31n-alkanes. Our results thereby highlight the need to carefully consider which n-alkane to use in hydroclimate δDwax reconstructions, and we discuss what information these differences may provide. Specifically, the divergence between aquatic and terrestrial δDwax may serve as a useful indicator of drought-induced evapotranspiration in this lacustrine setting.
How to cite: Hällberg, P., Smittenberg, R., Yamoah, K., Schenk, F., Chabangborn, A., Chawchai, S., Väliranta, M., and Wohlfarth, B.: Seasonal and Hydroclimatic Dynamics Revealed by δDwax and δ13Cwax in a Tropical Lake Core for the past 18 000 years, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18656, https://doi.org/10.5194/egusphere-egu25-18656, 2025.
Posters virtual: Wed, 30 Apr, 14:00–15:45 | vPoster spot A
EGU25-7582 | ECS | Posters virtual | VPS4
Application of Bound Biomarkers in the Evaluating the Deposition Environment and Maturity of ShaleWed, 30 Apr, 14:00–15:45 (CEST) | vPA.6
Bound biomarkers, which are covalently linked to kerogen or asphaltene macrostructures, exhibit enhanced stability against mixing effects, contamination, and biodegradation. Although previous studies have noted that the results of bound and free biomarkers in assessing sedimentary environment and maturity are not exactly consistent, specific criteria for assessing bound biomarkers have not been proposed. In this study, microscale sealed vessel catalytic hydrogenation (MSSV-Hy) was used to extract bound biomarkers from shale and compare them with free biomarkers. The study demonstrates the reliability of bound biomarkers indices in evaluating depositional environments and maturity, and it systematically compares the differences between bound and free biomarkers. The results revealed that the maturity assessment of bound biomarkers is lower than that of free biomarkers. Additionally, C29 regular steranes are selectively consumed during rapid heating, resulting in a decrease in the input parameters from terrigenous sources. Adjusted criteria for bound biomarkers can more accurately evaluate the sedimentary environment and maturity of shale.
请在此处插入您的摘要 HTML。
How to cite: Yuan, L.: Application of Bound Biomarkers in the Evaluating the Deposition Environment and Maturity of Shale, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7582, https://doi.org/10.5194/egusphere-egu25-7582, 2025.
