Sebastian Wetterich’s research while affiliated with TU Dresden and other places

Fossil proxy records in Last Interglacial (LIG, ca. 130–115 ka) lacustrine thermokarst deposits now preserved in permafrost can provide insights into terrestrial Arctic environments during a period when northern hemisphere climate conditions were warmer than today and which might be considered a potential analog for a near-future warmer Arctic. Still, such records are scarce on a circum-Arctic scale and often poorly dated. Even more, the quantitative climate signals of LIG permafrost-preserved deposits have not yet been systematically explored. Here, we synthesize geochronological, cryolithological, paleo-ecological, and modeling data from one of the most thoroughly studied LIG sites in NE Siberia, the permafrost sequences along the coasts of the Dmitry Laptev Strait, i.e., on Bol'shoy Lyakhovsky Island and at the Oyogos Yar coast. We provide chronostratigraphic evidence by new luminescence ages from lacustrine deposits exposed at the southern coast of Bol'shoy Lyakhovsky Island. The infrared-stimulated luminescence (IRSL) ages of 127.3±6.1 ka, 117.8±6.8 ka, and 117.6±6.0 ka capture the MIS 5e sub-stage, i.e., the LIG. The LIG lacustrine deposits are mostly preserved in ice-wedge pseudomorphs of 1-3 m thickness with alternating layers of peaty plant detritus and clayish silt. Ripples and synsedimentary slumping structures indicate shallow-water conditions. The rich fossil record was examined for plant remains (macro-fossils, pollen, sedaDNA), lipid biomarkers, and aquatic and terrestrial invertebrates (cladocera, mussels, snails, ostracods, chironomids, and beetles). Most proxy data and also paleoclimate model results indicate a regional LIG climate significantly (ca. 5 to 10 °C) warmer than today. Plant macrofossil data reflect mean temperatures of the warmest month (MTWA) of 12.7–15.3 °C for Oyogos Yar and 10.3–12.9 °C for Bol'shoy Lyakhovsky, while pollen-based reconstructions show mean MTWA of 9.0±3.0 °C and 9.7±2.9 °C as well as mean annual precipitation (MAP) of 271±56 mm and 229±22 mm, respectively. The biomarker-based reconstruction of the Air Growing Season Temperature (Air GST) using GDGTs is 2.8±0.3 °C. The fossil beetle-based mutual climatic range is 8 to 10.5 °C for MTWA and –34 to –26 °C for the mean temperature of the coldest month (MTCO) on Bol'shoy Lyakhovsky Island and 8 to 14 °C for MWTA and –38 to –26 °C for MTCO on Oyogos Yar. The chironomid-based MTWA varies between 9.4±1.7 and 15.3±1.5 °C and the water depth (WD) between 1.7±0.9 and 5.6±1.0 m on Bol'shoy Lyakhovsky Island. Prior findings from Oyogos Yar in the literature suggest an MTWA of 12.9±0.9 °C and a WD of 2.2±1.1 m. The first-time application of clumped isotopes to permafrost-preserved biogenic calcite of ostracods and bivalves reconstruct near-surface water temperature of 10.3±3.0 °C and bottom water temperatures of 1.5±5.3 °C in thermokarst lakes during summers. PaleoMIP Model simulations (PIobs+(lig127k-PI)) of the LIG show warmer MTWA compared to modern conditions (by 4.4±1.0 °C for Bol'shoy Lyakhovsky and 4.5±1.2 °C for Oyogos Yar) but currently underestimate the Eemian warming reconstructed from our multiple paleoecological proxies. The LIG warming mainly affected summer conditions, whereas modern and future warming will rather impact winter conditions. As the LIG annual mean temperature is often used as an analog for the future climate in the High Arctic, the proxy-model mismatch highlights the urgent need for more systematic quantitative proxy-based temperature reconstructions in the Arctic and more sophisticated Earth system models capable of capturing Arctic paleoenvironmental conditions.

Представлены результаты исследований ледового комплекса, озерных и озерно-аллювиальных отложений, выполненных на территории геологического памятника природы Мамонтова Гора в 2022-2023 гг. Оптически стимулированное люминесцентное датирование позволило установить, что формирование озерно-аллювиальных песков эльгинской свиты завершилось 250-242 тысяч лет назад (в конце оледенения МИС 8, перед межледниковьем МИС 7), а залегающих выше озерных алевритов - 138-126 тысяч лет назад (в конце оледенения МИС 6 и начале межледниковья МИС 5е). Средний изотопный состав сингенетических повторно-жильных льдов ледового комплекса (МИС 3) следующий: -(31 ± 2) ‰ по 18О; -(239 ± 15) ‰ по D; (8 ± 2) ‰ по dexc. Впервые получены данные по изотопному составу текстурных льдов ледового комплекса, средние значения которого составили -(26 ± 2) ‰ по 18О; -(201 ± 17) ‰ по D; (10 ± 4) ‰ по dexc. The results of studies of the Ice Complex, lacustrine, and lacustrine-alluvial sediments from the Mamontova Gora section performed in 2022-2023 are analyzed. Optically stimulated luminescence dating indicates that the formation of the lacustrine-alluvial sands of the Elga Group ended 250-242 ka ago, at the end of cold MIS 8, while the overlying lacustrine silts accumulated until 138-126 ka ago corresponding to the late cold MIS 6 - early warm MIS 5e. The average isotopic composition of the Yedoma Ice Complex (MIS 3) syngenetic wedge ice is -(31 ± 2)‰ for 18O, -(239 ± 15)‰ for D, and (8 ± 2)‰ for dexc. For the first time, we quantify the isotopic composition of the Yedoma Ice Complex textural ice with the average values of -(26 ± 2)‰ for 18O, -(201 ± 17)‰ for D, and (10 ± 4)‰ for dexc. The formation of lacustrine and lacustrine-alluvial sequences during MIS 7 and MIS 5e was fostered by warmer and likely longer thaw periods and associated permafrost thaw. The degree of warming remains to be estimated for this region.

The results of studies of the ice complex, lacustrine, and lacustrine-alluvial sediments from the Mamontova Gora section performed in 2022–2023 are analyzed. Optically stimulated luminescence dating indicates that the formation of the lacustrine–alluvial sands of the Elga Group ended 250–242 ka ago, at the end of cold MIS 8, while the overlying lacustrine silts accumulated until 138–126 ka ago corresponding to the late cold MIS 6–early warm MIS 5e. The average isotopic composition of the Yedoma Ice Complex (MIS 3) syngenetic wedge ice is –(31 ± 2)‰ for δ18O, –(239 ± 15)‰ for δD, and (8 ± 2‰) for dexc. For the first time, we quantify the isotopic composition of the Yedoma Ice Complex textural ice with the average values of –(26 ± 2)‰ for δ18O, –(201 ± 17)‰ for δD, and (10 ± 4)‰ for dexc. The formation of lacustrine and lacustrine–alluvial sequences during MIS 7 and MIS 5e was fostered by warmer and likely longer thaw periods and associated permafrost thaw. The degree of warming remains to be estimated for this region.

Rapidly changing permafrost landscapes are a potential key terrestrial source of greenhouse gases (GHGs) at a global scale, yet, remain poorly characterized regarding GHG origins and environmental controls on emissions. Subsurface ice wedges, commonly found across many permafrost landscapes, harbor GHG‐rich gas bubbles. Analyzing these bubbles aids comprehension of subzero temperature GHG formation in permafrost. The Batagay megaslump, Earth's largest known thaw slump in northern Yakutia, provides an opportunity to study mixing ratios and isotopic compositions of both GHGs and non‐GHG in ice wedge samples from two stratigraphic units: the Upper Ice Complex (UIC) and the Lower Ice Complex (LIC). The Ar/N 2 /O 2 compositions and bubble shapes indicated that the studied ice wedges were likely formed through dry snow and/or hoarfrost compaction, and microbial activity remained active after ice wedge formation. The high CO 2 and CH 4 mixing ratios and carbon stable isotope values suggested that CO 2 and CH 4 primarily originated from microbial sources. N 2 O showed an “exclusive relation” with CH 4 —meaning that high N 2 O is observed only when CH 4 is low, and vice versa—and N 2 O mixing ratios vary at different depths. These findings suggest that GHG formation in ice wedges is not solely controlled by physiochemical conditions, but involves a complex interplay between microbial activity and environmental conditions. Our study contributes to a better understanding of the dynamics involved in GHG formation within degrading permafrost landscapes.

Organic carbon (OC) in permafrost interacts with the mineral fraction of soil and sediments, representing < 1% to ~80% of the total OC pool. Quantifying the nature and controls of mineral-OC interactions is therefore crucial for realistic assessments of permafrost-carbon-climate feedbacks, especially in ice-rich regions facing rapid thaw and the development of thermo-erosion landforms. Here, we analyzed sediment samples from the Batagay megaslump in East Siberia, and we present total element concentrations , mineralogy, and mineral-OC interactions in its different stratigraphic units. Our findings indicate that up to 34 ± 8% of the OC pool interacts with mineral surfaces or elements. Interglacial deposits exhibit enhanced OC-mineral interactions, where OC has undergone greater microbial transformation and has likely low degradability. We provide a first-order estimate of ~12,000 tons of OC mobilized annually downslope of the headwall (i.e., the approximate mass of 30 large aircrafts), with a maximum of 38% interacting with OC via complexation with metals or associations to poorly crystalline iron oxides. These data imply that over one-third of the OC exposed by the slump is not readily available for mineralization, potentially leading to prolonged OC residence time in soil and sediments under stable physicochemical conditions.

Retrogressive thaw slumps (RTS) are an important landform of rapid permafrost degradation in regions with very high ground ice contents. RTS mobilize significant amounts of sediment, meltwater and organic carbon and impact downstream hydrological systems by directly affecting topography and water quality. The term megaslump has previously been coined for RTS exceeding 20 ha in size. The Batagay megaslump in the Yana highlands of NE Siberia with an area of 87.6 ha (in 2023, including the bowl-shaped part and the erosional outlet) has been identified as the largest megaslump on Earth. We use very high resolution remote sensing from satellite data and drones, geological structure modeling, and field data to assess how much and what material is thawed and mobilized in the Batagay megaslump. The total volume of permafrost thaw and material loss from the Batagay RTS amounts to about 1 million m3 per year. The material is by one third composed of thawed sediments and by two thirds of melted ground ice. About 4000 to 5000 tons of previously permafrost-locked organic carbon is released every year. Organic carbon content has been measured as Total Organic Carbon (TOC) of sediments and as Dissolved Organic Carbon (DOC) of ground ice. From its formation in the 1970s until 2023, the Batagay RTS – due to thermal denudation and headwalls retreat – mobilized a total volume of about 34.7 million m3 of which 23.4 million m3 were melted ground ice and 11.3 million m3 were thawed deposits including a total of about 169,500 t organic carbon. With these rates of sediment and carbon mobilization, the Batagay megaslump is not only a prominent local feature of rapid permafrost thaw, but offers excellent conditions to study rates and mechanisms of rapid permafrost degradations and to calculate the stock and release of, e.g., organic matter.

The climate warming–related degradation of permafrost can lead to the entry of climatically and biologically active substances, including mercury, into the biosphere; this work focuses on the analysis of the total content of mercury and organic carbon in 15 cores drilled in frozen Quaternary deposits of the Arctic Archipelago of Spitsbergen. The mercury content was additionally analyzed in bedrock samples, because the studied Quaternary deposits are formed by the weathering of the bedrock of the area. The results show that mercury concentrations in 157 studied samples of frozen Quaternary deposits range from 21 to 94 ng/g, with an average value of 40 ng/g. The expected correlation of mercury content with organic carbon content is not revealed. There are no trends in the accumulation of mercury depending on the lithological facies, geomor-phological position, the time of sedimentation, or the freezing conditions. The average content of mercury in bedrock is relatively low, with a mean value of 8 ng/g. This means that the main source of mercury in frozen Quaternary deposits is not bedrock, but the formation of organic matter complexes or sorption on clay parti-cles. In terms of the ongoing discussion about mercury input from permafrost to ecosystems, the results obtained from boreholes can be considered preindustrial background values.

The Batagay megaslump, in the Yana Uplands of northern Yakutia, Russia, is the largest known retrogressive thaw slump in the world. The slump exposes a remarkable sequence of Ice Age permafrost deposits that record the interaction of colluvial, eolian and periglacial processes on a hillslope episodically forested during the last 650 ka or more in response to climate variability on glacial–interglacial timescales. Numerous bones, teeth, and occasional carcasses of Pleistocene and Holocene mammals have been recovered from the permafrost. The megaslump developed over the course of several decades in three stages: (1) gullying, (2) thaw slumping, and (3) megaslumping. After disturbance to the taiga vegetation cover in the 1940s–1960s, a hillslope gully formed by the early 1960s. The gully initiated thaw slumping along its central part during the 1980s, with the slump enlarging to megaslump (>20 ha) proportions during the 1990s. By 2019, the area of the slump had reached about 80 ha and its headwall above the slump floor was up to about 55 m high. The main geomorphic processes of slump growth are headwall ablation and thermal erosion, producing a distinctive terrain of icy badlands on the slump floor. Though much of the megaslump is rapidly growing at present, it will probably stabilize eventually as an irregular terrain characterized by sandy ridges and sand‐filled elongate depressions formed by degradation of the badlands. Comparison of the Batagay megaslump with megaslumps from northwest Canada reveals several similarities and differences in terms of their geomorphology, permafrost deposits, and Quaternary history.