Understanding past variability of the Asian monsoon system is essential for constraining its sensitivity to ongoing and future climate change. High Asia, encompassing the Tibetan Plateau and surrounding regions of China, Nepal, and Mongolia, represents a key area where the Indian Summer Monsoon, East Asian Summer Monsoon, and mid-latitude westerlies interact. This contribution synthesizes paleoclimate reconstructions from this region with a primary focus on lacustrine ostracod records, complemented by a wide range of established climate proxies reported in the literature, including pollen, diatoms, sedimentological indicators, geochemical proxies, loess sequences, and ice-core records. Central Asia is selected to provide a broader atmospheric and hydrological context, though the emphasis remains on monsoon-influenced regions to the south and east.

Ostracods are particularly valuable paleoclimate indicators due to their sensitivity to changes in temperature, salinity and generally lake-water chemistry. Variations in ostracod assemblage composition, species diversity, and stable isotope and elemental geochemistry (δ¹⁸O, δ¹³C, Mg/Ca, Sr/Ca) are used to infer past effective moisture and monsoon intensity. These records are evaluated alongside pollen-based vegetation reconstructions and sedimentary evidence for lake-level fluctuations, allowing for a robust, multiproxy assessment of regional climate evolution from the late Pleistocene through the Holocene.

The compiled records reveal strong spatial and temporal heterogeneity in monsoon behavior across High Asia. Periods of enhanced monsoon activity are generally associated with expanded lakes, lower salinity, increased ostracod diversity, and forest or grassland pollen taxa, whereas weakened monsoon phases correspond to salinity-tolerant ostracod assemblages, steppe-dominated vegetation, and increased aridity, particularly in Mongolia and northern Tibet.

How to cite: Schmitz, O.: Reading the Record of Lakes: What Ostracods Tell Us About Central Asian Changing Environments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13576, https://doi.org/10.5194/egusphere-egu26-13576, 2026.

The Indian and East Asian Summer Monsoons are key atmospheric controls on hydrological variability across the Tibetan Plateau. This region, often referred to as the Asian Water Tower, provides freshwater resources for approximately two billion people via the major river systems that originate there. Consequently, reliable hydrological projections require improved constraints on the timing, duration, and magnitude of climate variability, and an understanding of the environmental responses to this change, in this climatically sensitive high-altitude region, particularly over long geological timescales.

Nam Co is one of the largest and deepest lakes on the Tibetan Plateau (4,718 m a.s.l.; 2,020 km² surface area; 98.9 m max. water depth; 10,680 km² catchment area) and is an exceptional archive for investigating long-term climatic and environmental variability. To reconstruct past long-term climate variability and to examine its impacts, the lake was chosen as a target for ICDP drilling (NamCore) to recover a long, continuous record, with the aim of examining paleoenvironmental evolution, geomicrobiology, tectonics, and paleomagnetism. During the field operations conducted between May and July 2024, a total of 1415.45 m was drilled and 1175.99 m cored with 950.77 m of sediment recovered (core recovery of 80.8 %). Comparisons between magnetic susceptibility from (i) borehole logging, (ii) whole-round sediment cores, and (iii) core catcher material show widely similar trends across the depth dimension, suggesting a highly accurate depth control of the drilling depths recorded.

Here, we present an overview of the project and sedimentological perspectives on the recovered sequence based on an integrated dataset comprising (i) core catcher material, (ii) sediment core samples and (iii) spectrophotometer and magnetic susceptibility measurements supported by (iv) detailed lithostratigraphic descriptions. The NamCore sedimentary succession is subdivided into five lithological units, defined by variations in (i) carbonate content and carbonate mineralogy, (ii) grain-size distributions, (iii) colour (likely related to iron speciation), and (iv) frequency-dependent magnetic susceptibility. The succession is characterised by recurring transitions among four lithofacies: (i) calcareous mud, (ii) ferric-stained calcareous mud, (iii) fine- to medium-grained sand, and (iv) non-calcareous mud. These alternations are interpreted to reflect major climatic and/or environmental changes, including variations in water-column, redox conditions, sediment accumulation rates, fluctuations in the extent of surrounding mountain glaciers, and broader-scale shifts in atmospheric circulation over the Tibetan Plateau associated with glacial–interglacial climate variability, changes in Pleistocene climate boundary conditions and related changes in catchment processes. In particular, colour shifts (green/red, a*) may represent shifts between warmer and wetter to colder and drier climatic conditions, whereas variations in frequency-dependent magnetic susceptibility likely reflect changes in pedogenesis, both of which might be linked to large-scale hydroclimatic forcing.

How to cite: Adolph, M.-L., Wang, J., Zhu, L., Clarke, L. J., Henderson, A. C. G., Vogel, H., Daut, G., Ju, J., Spiess, V., Ulfers, A., Zhaxi, C., Zeeden, C., and Haberzettl, T.: A sedimentological characterisation of a 510 m lacustrine sequence recovered from the ICDP Nam Co Drilling Project (NamCore), Tibet, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5385, https://doi.org/10.5194/egusphere-egu26-5385, 2026.

How to cite: Ju, J., Zhu, L., Wang, J., Kai, J., and Zhu, X.: Observations of modern processes in Nam Co, Tibetan Plateau, China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12623, https://doi.org/10.5194/egusphere-egu26-12623, 2026.

Microplastics (MPs) are persistent contaminants in freshwater systems, yet their long-term accumulation patterns and dominant drivers in inland lakes remain poorly constrained. Here, we reconstruct microplastic deposition over the past ~200 years using a sediment core from Lake Liangzi, located in the middle–lower reaches of the Yangtze River, China. A robust ²¹⁰Pb–¹³⁷Cs chronology was established for the upper 66 cm of the core (ca. 1823–2019). Microplastics were extracted at 1 cm resolution, and their abundance, size, shape, and colour were quantified by optical microscopy, with polymer composition identified using micro-Fourier transform infrared spectroscopy (μ-FTIR). The results show a pronounced increase in MP abundance through time, with clear phase shifts. CONISS cluster analysis distinguishes three stages: a low-background period prior to 1957, a phase of moderate increase between 1958 and 1984, and a period of rapid accumulation since 1984. Microplastic abundance is positively correlated with total organic carbon (TOC) and total nitrogen (TN), indicating close coupling with sedimentary organic matter enrichment. Redundancy analysis demonstrates that anthropogenic factors, particularly plastic production, population growth, fisheries activity, economic development, and land-use change, explain most of the variance in MP accumulation, whereas climatic variables play a comparatively minor role. Analysis of land-use change between 1980 and 2020 reveals expanding built-up areas and declining cropland, consistent with intensified urbanization and increased microplastic inputs. Together, these results provide clear sedimentary evidence that human activities are the dominant drivers of long-term microplastic accumulation in inland lake sediments, highlighting the growing legacy of plastic pollution in freshwater ecosystems.

How to cite: Zhang, J., Meadows, M. E., Zhang, K., Lin, Q., Hou, J., and Jin, Y.: Historical reconstruction of microplastic accumulation in shallow lake sediments and its anthropogenic drivers: A case study in Lake Liangzi, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8702, https://doi.org/10.5194/egusphere-egu26-8702, 2026.

Beyond being emerging contaminants, microplastics (MPs) may serve as novel environmental proxies for the Anthropocene; yet the links between their accumulation in sediments and the evolution of shallow lakes under human-nature interactions remain unclear.  In this study we reconstruct MP sedimentary sequences of three sediment spanning the past 80 years in Baiyangdian Lake, North China. Evidence derived from Analyses using Rate of Change (RoC), coupling models, and Partial Least Squares Path Modeling (PLS-PM) indicate that MP sedimentary patterns during this period underwent two critical transitions, viz. an initial increase triggered by weakened hydrological connectivity due to dam construction in 1963, and a subsequent accelerated accumulation phase driven by intensified human activities in the the catchment from around 2000. Spatially, MP abundance in cores DC-1 (mean 37,229.7 items kg^-1) and CPT-1 core (8,493.0 items kg^-1), was significantly greater than in core SCD-1 (3,648.6 items kg^-1), located within the nature reserve.  Random Forest modeling further reveals that nutrient accumulation and hydrodynamic intensity jointly drive spatial heterogeneity in MP abundance. Together, these findings suggest that MPs can serve as effective indicators of anthropogenic intensity and provide important insights into the mechanisms shaping the environmental evolution of shallow lakes during the Anthropocene.

How to cite: Zuo, Y., Ge, Y., Meadows, M., Zhang, K., and Li, Y.: Tracing the Anthropocene through microplastic sedimentary records: Drivers and spatiotemporal heterogeneity in Baiyangdian Lake, North China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8688, https://doi.org/10.5194/egusphere-egu26-8688, 2026.

Lake sediments are critical archives of past environmental changes, yet interpreting the complex biogeochemical processes governing carbon sequestration remains a significant challenge. Our previous work in Lake Liangzi (Hou et al., 2026, Water Research) highlighted a paradox: eutrophication-driven ecological regime shifts increased organic matter inputs but ultimately weakened long-term carbon burial. This motivates the need for integrative approaches that can resolve the molecular-level controls governing the fate of sedimentary organic matter.
Here, we propose a machine-learning-assisted framework that integrates ultra-high-resolution mass spectrometry (FT-ICR MS) with data-driven analysis to explore these controls. We analyze a sediment core spanning nearly two centuries to construct a comprehensive matrix of thousands of unique organic molecules and their intrinsic chemical properties (e.g., O/C, H/C, AI_mod). Based on operational persistence criteria, molecules are classified into distinct fate categories reflecting their stability.
Using these fate classifications, our primary goal is to train and interpret an XGBoost model to test the hypothesis that molecular fate can be inferred from chemical properties alone, and to identify candidate molecular characteristics that may govern carbon persistence. In parallel, molecular transformations between adjacent sediment layers are examined to reveal potential shifts in dominant biogeochemical reaction pathways associated with historical ecosystem changes.
Finally, we explore the use of model performance itself as a diagnostic proxy for ecosystem stability. This approach is designed to assess the hypothesis that periods of ecological transition are associated with reduced predictability of biogeochemical processes. Overall, this study presents a transferable analytical strategy aimed at extracting process-oriented insights from lake sediment archives, highlighting the potential of machine-learning-guided approaches to advance limnogeology beyond descriptive reconstruction.

How to cite: Hou, J., Meadows, M., and Zhang, K.: Decoding Molecular Controls on Carbon Sequestration in Lake Sediments Using Machine Learning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8580, https://doi.org/10.5194/egusphere-egu26-8580, 2026.

How to cite: Laakkonen, A., Thomas, C., Moser Roeggla, P., Adolph, M.-L., Ceriotti, G., Berg, J., Kipfer, R., Haberzettl, T., Ju, J., Henderson, A., Clarke, L., Zhu, L., Wang, J., Foubert, A., and Vogel, H.: Diagenetic formation pathways of pyrite in Nam Co, a high-altitude Tibetan lake  , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9076, https://doi.org/10.5194/egusphere-egu26-9076, 2026.

The Yan'an Formation in the Ordos Basin and the Xintiangou Formation in the Sichuan Basin are typical lake facies sedimentary formations developed in the Alinian period. They contain a large amount of organic-rich fine-grained sedimentary rocks and are the main sites for shale oil and gas enrichment. In this study, geochemical tests, including major, trace, and rare earth elements and TOC tests, were carried out on the fine-grained sedimentary rocks of the shallow lake Yan'an Formation and deep lake Xintiangou Formation to reconstruct their depositional palaeoenvironments, and to explore their organic matter enrichment mechanisms in different depositional environments under lithological differences. The conclusions of this study are as follows: 1) The total organic carbon (TOC) of fine-grained sedimentary rocks increases with increasing mud content and decreasing grain size; 2) The palaeoenvironments of the fine-grained sedimentary rocks in the shallow and deep lake facies are generally consistent, but the redox conditions and deposition rate of the water column in the deep lake facies are stronger than those in the shallow lake facies, while the input of terrigenous detrital, palaeosalinity, and stagnant environment are relatively weaker; 3) The organic matter enrichment mode of lake facies fine-grained sedimentary rocks is a typical palaeoclimatic and palaeoproductivity-dominated “Production mode”; 4) The difference in depositional environments under lithological differences is mainly related to productivity factors, such as palaeoclimate (CIA) and palaeoproductivity (P/Ti). The results of this study help to understand the formation mechanism of lake facies fine-grained sedimentary rocks, distinguish the hydrocarbon generation potential of different lithologies, and provide a basic geological theoretical basis for the exploration of shale oil and gas in the study area.

How to cite: He, Q. and Xu, S.: Organic matter enrichment and palaeoenvironmental comparison of Alinian fine-grained sedimentary rocks in lake facies, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1988, https://doi.org/10.5194/egusphere-egu26-1988, 2026.

Enhanced seasonal to interannual climate variability associated with changes in El Niño–Southern Oscillation (ENSO) can intensify wet and dry seasons extremes in the tropical western Pacific. Characterizing long-term and high-resolution changes in ENSO is crucial for our understanding of the tropical Pacific hydroclimate and its associated global-scale teleconnections. In this study, we anlayze sedimentary records from Lake Poso, a large (up to 400 m deep) tectonic lake on Sulawesi Island at the western edge of the Pacific warm pool. Stratification of Lake Poso’s water column below ~90 m depth is documented by anoxia, elevated concentrations of redox-sensitive metals and nutrients at depth in the water column, and the presence of finely laminated sediments. The reduction of rainfall and regional humidity during the dry season is increased during El Niño-liked events. Water column temperature monitoring data collected between the end of 2022 and early 2024 exhibit surface temperature cooling and deeper vertical water column mixing down to depths below the ~90 m oxycline during the dry season. This effect was particularly exacerbated during the 2023 El Niño event, suggesting a direct relationship between climate variability and water column structure.

To assess how such climate-induced mixing variability is recorded in the sediments, we examine three short sediment cores retrieved along a depth transect spanning oxic, transitional, and anoxic depositional environments in Lake Poso. Sedimentary structures change systematically with water depth, with massive sediments above the oxycline, to massive sediments with intermittent lamination in the transition zone, to continuously laminated sediments below the oxycline. The spatial and temporal variability in sedimentary structures suggests past changes in mixing depth and lake level linked to variations in dry-season intensity. Furthermore, longer sediment piston cores from three locations were recovered from sites above the oxycline at paleoshoreline locations identified by seismic surveys. These records show repeated transition from sandy, structureless nearshore deposits to laminated fine-grained sediments, indicating multiple substantial decimeter-scale changes in lake level on longer time scales. Changes in sediment structure and composition in Lake Poso are therefore prime indicators of past changes in West Pacific Warm Pool hydroclimate.

How to cite: Damanik, A., Shore, M., Cahyarini, S. Y., and Vogel, H.: Lake Poso as a ‘rain gauge’ in the tropical western Pacific: insights into ENSO variability from laminated sediments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4136, https://doi.org/10.5194/egusphere-egu26-4136, 2026.

Lake Liangzi, a shallow floodplain lake in the middle reaches of the Yangtze River, is listed in the Asian Wetland Protection Directory for its critical ecosystem services. However, the loss of ecological resilience in macrophyte-dominated lakes subjected to long-term eutrophication pressure is often underestimated when dense vegetation cover persists. Using a continuous 2,500-year sedimentary sequence, we reconstruct the long-term ecological evolution of Lake Liangzi through the integration of sedimentary ancient DNA (sedaDNA), plant functional traits (life form and canopy height), and multi-proxy geochemical indicators. The sediment record reveals three distinct ecosystem phases. During an early stable state (2610–1550 cal yr BP), oligotrophic conditions supported diverse submerged and floating-leaved macrophyte communities within a modular ecological network. This was followed by an adaptive transition phase (1550–344 cal yr BP), during which early anthropogenic disturbance increased nutrient inputs and promoted opportunistic taxa, while overall community evenness and resilience were maintained. In the most recent phase (344 cal yr BP–present), intensified catchment erosion and eutrophication progressively degraded underwater light conditions. Rather than collapsing, the ecosystem persisted through trait-mediated adjustment: the canopy-forming species Potamogeton maackianus achieved monodominance by increasing community-weighted plant height, competitively excluding floating-leaved and benthic taxa. Sedimentary network reconstructions indicate that this persistence masked a fundamental structural shift from a diverse, modular system to a highly connected and fragile regime. Our results demonstrate how long-term sedimentary archives can reveal “cryptic degradation” processes that are not evident from present-day vegetation cover alone. This study highlights the value of multi-proxy lake sediment records for quantifying long-term ecosystem trajectories, resilience loss, and the delayed risks of regime shifts in human-impacted freshwater systems.

How to cite: Ren, J., Meadows, M., Zhang, K., Lin, Q., and Jin, Y.: A 2,500-year sedimentary record reveals cryptic ecological degradation in a macrophyte-dominated Yangtze floodplain lake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8691, https://doi.org/10.5194/egusphere-egu26-8691, 2026.

Global climate change of last two millennium and associated hydroclimatic variations in central and southern Mexico have been linked to the socio-cultural transitions at several Mesoamerican urban centers. The increase in well-mixed greenhouse gases since the industrial revolution, however, has led to an ascent in mean temperature, and the projections for later part of this century include further depletion in precipitation and soil moisture, affecting the crop yield and immigration both from the rural and urban regions of Mexico. New multi-proxy paleoclimate data about the droughts since the LGM were inferred from the sedimentary archives of Lake Totolcingo (19°N) and paleo-lake Cieneguilla (22°N), located at the east and northeast of Mexico with similar precipitation regimes (summer-autumn) and moisture sources, i.e. the Atlantic Ocean. Both the basins are present-day agriculture hubs and situated close to important Classic and Postclassic archeological sites. The lake area mapping and stable isotope compositions of surface water reflected the annual precipitation and its seasonality. Paleoclimate records obtained from the stable isotopes (C, H and N), grain size, magnetic property and elemental concentrations in organic and inorganic components of the lacustrine archives suggested homogeneity in the organic productivity during the latest Pleistocene deglaciation with the millennial-scale fluctuations in catchment erosion and lake water salinity coupling with the oxygen isotope fractions of Greenland ice core and dynamics of ITCZ position during the stadial and interstadial. Recurrent droughts over the Holocene were reflected in enhanced aeolian activity in lake catchments, reduced runoff and more carbonate deposition. Enhanced aridity was also reflected in organic productivity dominanted by C4 plants. This arid interval in orbital-scale was coupled with phases of low spring insolation and high autumn insolation and decoupled from the Greenland ice core and ITCZ dynamics. The first-order similarity with Golf of Mexico SST suggested autumn insolation modulated warmer Atlantic surface water was the principal driver of droughts. This multiproxy dataset addresses challenges from the interbedded tephra layers and possible hiatus for accurate regional climate reconstructions and furture uncertainities from the global warming.

How to cite: Roy, P. D., Garcia-Arriola, A., Martinez-Dyrzo, H. B., Sanchez-Zavala, J. L., and Giron-Garcia, Ma. P.: Recurrent droughts over the Holocene compared to the wetter deglaciation at eastern and northeastern Mexico and decoupling of the forcing mechanisms, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8044, https://doi.org/10.5194/egusphere-egu26-8044, 2026.

Sediment records have been widely used to reconstruct Holocene environmental and climate conditions around the world. Despite the climatic sensitivity of northern South America, paleoenvironmental studies remain limited, particularly regarding ecosystem responses to Late Holocene climate fluctuations. Here we present a multiproxy reconstruction based on a radiocarbon-dated sediment core retrieved from the Nechí wetland, located in the Lower Cauca region of the Antioquia Department (LCA), Colombia, documenting environmental changes over the past ~2,500 years. We combined sedimentological, XRF, and palynological analyses to reconstruct the vegetation changes and their response to climate events. The results indicate that the region experienced a general wetter trend and massive floods over the last 2,500 years, with a pronounced climate anomaly dominated by droughts and a reduction in flood pulses occurring between 1,000 and 1,300 CE. A peak of ecological change took place ca. 1,100 CE, characterized by a clear turnover in pollen assemblages toward herbaceous (e.g., Asteraceae) and disturbance taxa (e.g., Cecropia), indicating a change in climate conditions and instability of forest cover over an interval of ~250 years, spanning roughly from ca. 950 to 1,200 CE. After ca. 1,300 CE, an increase of Symmeria and pollen taxa associated with flooded areas suggests the return of wetter conditions and a reduced ecological change. We suggest that this transition was strongly influenced by the Late Holocene Climate Anomaly, a period of increased climate instability documented across tropical South America. Vegetation trends over the last 500 years demonstrate substantial losses of forest cover associated with human activities in the region and an increase in open areas and disturbance-associated vegetation. This study highlights the sensitivity of lowland wetland ecosystems in the LCA region to Late Holocene climate variability. It provides new insights into the interaction and timing between climate, hydrology, and vegetation in northern South America.

How to cite: Duarte, E., Franco-Gaviria, J. F., Escobar, J., Correa-Metrio, A., Curtis, J. H., Hoelzmann, P., and Nykamp, M.: Late Holocene climate variability and associated paleoenvironmental changes in northern South America, Colombia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8412, https://doi.org/10.5194/egusphere-egu26-8412, 2026.

It is important to accurately classify shale lithofacies and identify their origin and hydrocarbon content for both shale oil and gas reservoirs. Oil-bearing lacustrine shales (average TOC content=3.12 wt%, average Ro=0.81%) of the lower third member (Es3L) of the Eocene Shahejie formation in the Zhanhua Sag, Bohai Bay Basin contain eight lithofacies that are differentiated based on mineralogy, total organic carbon content (TOC), grayscale, elemental composition and Rock-Eval pyrolysis data. The results show that four lithofacies are most common: moderately organic-rich laminated calcareous shale, organic-rich laminated calcareous shale, and organic-rich calcareous/massive mixed shale. Paleoenvironment controls lithofacies evolution. Unit 1 (arid): Limited detrital/nutrient inflow and low water energy, coupled with transgression-induced high salinity suppressed freshwater bioproductivity, favoring moderately-enriched laminated calcareous shale. Unit 2 (transition): Increased productivity promoted organic-rich laminated calcareous shale. Unit 3 (humid): Nutrient and detrital input (TOC undiluted) in the lake increases; however, the destruction of the quiet water environment leads to the gradual disappearance of laminae, shifting lithofacies to organic-rich massive calcareous and organic-rich massive mixed shales, moderately-enriched laminated calcareous shale, organic-rich massive calcareous shale, and organic-rich massive mixed shale that have high shale oil potential. Two high-brittleness and high-oil sweet-spot intervals were identified (2988 m~3012 m and 3108 m~3124 m in well A): interval 2 is enriched in situ hydrocarbon via high TOC and large storage; interval 1, despite lower TOC, accumulated migrated hydrocarbons via micromigration and large reservoir space.

How to cite: Wang, Y., Xu, S., and Hao, F.: Sedimentary evolution and shale oil potential of Shahejie Formation in Zhanhua Sag, Bohai Bay Basin, China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1789, https://doi.org/10.5194/egusphere-egu26-1789, 2026.

Limnological seismites are sedimentary layers within lacustrine deposits that have been deformed by earthquake-induced shaking. They are critical indicators of paleoseismic activity, providing a record of past earthquakes. The longest continuous earthquake record on Earth, 220-kyr-long, recovered from the 460-m-long drill core at the depocenter of the Dead Sea, is interpreted based on recognition of such seismites. The identification of seismites in the Dead Sea deep drill core relies on comparison with detailed structural analyses of seismites exposed along extensive outcrops around the Dead Sea. Many of these seismites are juxtaposed as well with syn-depositional faults, and those that were formed in historical times are tightly correlated with historical records and damaged archaeological sites. The key to characterizing earthquakes is understanding the physics of the seismite's deformation mechanisms. Here we focus on one of the robust mechanisms by which shear instability, of the type of Kelvin-Helmholtz instability, deforms stably stratified fluids. We performed state of the art direct numerical simulations of viscoplastic rheology, with nonlinear relations between the stress and the deformation rate tensors, to study the deformation response of the lacustrine sediments to earthquake-imposed shear. First, we measured the viscoplastic rheological characteristics of samples of Dead Sea sediments (aragonite, detritus and their mixture), by using rotary shear. We found substantial expected differences between the ductile detritus and the brittle aragonite. These data were implemented in the numerical simulations to solve the full Navier-Stokes fluid equation. The comparison between the simulations and the in-situ exposed deformations allows us to constrain the intensity and the peak ground acceleration of their generating paleo-earthquakes.

How to cite: Heifetz, E., Le Blanc, A., Marco, S., Siman Tov, S., and Levy, J.: Limnological seismites as a record of past earthquakes in the Dead Sea Rift, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22374, https://doi.org/10.5194/egusphere-egu26-22374, 2026.

Sedimentary records retrieved from Walden Pond, Concord, MA and Sluice Pond, Lynn MA show evidence of mass wasting likely triggered by strong historic and prehistoric groundshaking. The two lakes of glacial origin form steep-sided basins of 30 m and 20 m maximum water depth with Walden Pond being divided into three distinct subbasins. Because of the visually homogeneous nature of the organic-rich lacustrine muds we employed a combination of sedimentological, geophysical, geochemical, and palynological proxies to characterize background sediments and the fingerprint of the M=5.9 1755 Cape Ann earthquake, the largest historic earthquake in New England. We then used a similar multiproxy approach to investigate the longer record of Sluice Pond as well as the individual records of the three basins of Walden Pond extending the paleoseismic record about 800 years back in time. Robust age models using a combination of radioisotopes, industrial contaminants, and pollen stratigraphy allow for dating of event horizons as well as correlation between different lake basins. Deposited before the arrival of Europeans settlers, sediments in both lakes are composed of organic-rich mud reflecting a forested landscape. The rise of non-arboreal pollen including Ambrosia record the widespread logging practices of European settlers in New England starting in the mid-17^th century. Subsequent erosion of soils is marked by grain size decrease, lower organic matter content, and elemental compositions characteristic of local soils. Separate from these long-term trends we identified sediment horizons that mark sudden-onset events. These are typically characterized by larger grain size, influx of nearshore palynomorphs, higher bulk densities, and/ or lower organic matter content. We interpret these horizons as underwater mass wasting events. For Sluice Pond, we were able to identify two event horizons, one associated with the M=5.9 1755 Cape Ann earthquake, and another one dated to between 1390 -1510 CE. For Walden Pond, sediments show synchronous mass wasting in at least two subbasins potentially related to the historic 1755 earthquake, as well as two older events dated to between 1380-1520 CE and 1050-1320 CE. Interestingly, a cluster of landslides in southern Maine within geotechnically sensitive clays dates to 1220-1450 CE and could correlate with the disturbed lake sediments. We analyzed the spatial distribution of event horizons in the two lakes in Massachusetts and landslides in Maine and identified possible source areas and magnitudes of prehistoric earthquakes with one possible source area within the Littleton, MA seismic zone. Our analysis suggests that the seismic hazard in the Boston area might be higher than previously appreciated.

How to cite: Monecke, K., Ebel, J., Hubeny, B., McCarthy, F., Theis, L., and Aaron, A.: Paleoseismic Investigations of Organic-rich Lake Sediments in New England – a Multiproxy Approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15964, https://doi.org/10.5194/egusphere-egu26-15964, 2026.

Two joint Canadian-German expeditions at Lake Wiyâshâkimî (56.2°N, 74.4°W) were devoted to limnogeological research of the deglacial history of the Laurentide Ice Sheet in northeastern Canada. The lake is located on the Canadian Shield, roughly 150 km east of the southern Hudson Bay coast. It was formed by two meteorite impacts in the late Ordovician and early Permian. The intersected double crater structure of the 60 x 30 km large and up to 178 m deep lake is preserved until today. During the Quaternary, it was repeatedly covered by the Laurentide Ice Sheet. A hydrolological survey in summer 2023 confirmed the oligotrophic nature and well mixed water column of the freshwater lake. Geophysical subbottom profiling exhibited an ice-scoured bottom of the lake floor with only a thin veneer of postglacial mud. An 8 m-long sediment core was taken in spring 2024 at 110 m water depth within a depression including a pocket of preserved older sediments. Sediment analytics comprised radiocarbon dating, smear-slide studies, elemental x-ray scanning, determination of total organic carbon and nitrogen, pollen analysis as well as stable-isotope analysis of organic carbon (δ¹³C) and oxygen of diatom frustules (δ¹⁸O). The lower 6.5 m of the sediment core sequence comprises meltwater sands partly varve-like laminated. Radiocarbon ages of this interval scatter around 30 cal ka BP and are difficult to ascertain, because of reworked older organic matter. The sand is overlain by a 0.65 m thick grayish clay layer with a basal age of 22 cal ka BP. It provides evidence for stagnant glaciolacustrine conditions below or in front of the retreating Laurentide Ice Sheet. The deposition of brownish diatom-bearing organic muds started at 6.5 cal ka BP. Pollen data indicate Holocene reforestation in the catchment since that time. This timing is well consistent with geomorphological evidence of regional glacial decay. Based on geochemical indicators, there is no evidence for a marine incursion related to the 8.2-ka event.

How to cite: Diekmann, B., Meyer, H., Biskaborn, B. K., Allertseder, P., Freundt, S., Andreev, A., Sarrazin, D., Zimmermann, C., and Pienitz, R.: Last Glacial to Holocene lacustrine Environment of a large Impact Lake in the Subarctic of northeastern Canada: Implications for former Meltwater Events, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10615, https://doi.org/10.5194/egusphere-egu26-10615, 2026.

Lake Grundlsee, located in the Northern Calcareous Alps, is one of three large, deep, elongate lakes in the southern Salzkammergut region in Austria. The lake is situated in a geologically complex setting characterized by widespread evaporites of the Haselgebirge Formation to its south, which are known to promote a wide range of mass movement processes in the region. Recent research from the adjacent Bad Aussee Basin, which hosts an at least 880-m-thick Pleistocene sedimentary succession, indicates that Quaternary salt-tectonic activity is an important but still underexplored influencing factor on regional landscape evolution. Understanding these dynamics requires long-term records that extend beyond historical documentation. Bathymetric data and lacustrine sediment archives from neighboring Lake Hallstatt and Lake Altaussee have demonstrated the potential of such records for reconstructing Alpine landscape evolution and mass movement activities. However, neither subsurface geology nor in-depth sedimentological studies were performed on the adjacent Lake Grundlsee so far.

In this study, we present a comprehensive geologic and hydrographic survey of Lake Grundlsee. It consists of a high-resolution bathymetric survey of the lake basin and a seismic reflection profile survey supplemented by sediment core extraction from the lake bottom.  

The bathymetric data was collected in July 2025 using a Teledyne T50 multibeam echosounder (MBES), operated at 400 kHz with lakebed backscatter registration for lake floor classification purposes. The resulting 3D bathymetric model of Lake Grundlsee shows a maximum water depth of approximately 63 m and a complex lake floor morphology.

The bathymetric data reveals numerous previously unknown subaqueous landslides distributed throughout the basin, with particular concentrations in the eastern sub-basin and along the northern slope. Multiple generations of mass movements are evident, including older, partially overprinted deposits. The largest landslides show runout lengths exceeding 600 m and scar widths of over 250 m.

Reflection seismic profiles of a total length of ~40 km were obtained in November 2025 using an Innomar parametric sub-bottom profiler operating at 12 kHz. The narrow low-frequency sound beam images the subsurface geometry of these deposits with high resolution and with penetration depths of up to 10m providing insight into deposit thickness, failure planes, and stratigraphic context. Associated turbidite deposits are traceable across the basin floor.

In order to investigate the lithological characteristics of the uppermost sedimentary sequences a total of 18 sediment cores were retrieved in November 2025 using a gravity corer with hammer system.

Hydrogeological and geomorphological mapping of the surrounding catchment, documenting the distribution of evaporites and mass movement deposits around Lake Grundlsee, contextualizes the subaqueous findings and helps identify potential source areas and predisposing geological conditions.

The causes of slope failure remain under investigation. Possible triggering mechanisms include spontaneous gravitational instability on steep subaqueous slopes, seismic shaking — as suggested by studies in neighboring lakes such as Lake Altaussee — and salt-related subsurface processes associated with the underlying Haselgebirge Formation as well as human-induced failures.

This study provides a baseline for future hazard assessment and demonstrates the value of integrating subaqueous and terrestrial geomorphological approaches in Alpine lake research.

How to cite: Heine, E., Ortler, M., Schmalfuss, C., Leitgeb, L., Taeubling-Fruleux, B., and Moernaut, J.: Reconstructing subaqueous mass movements in Lake Grundlsee (Styria, Austria), a key record for understanding geohazards in a complex Alpine setting, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11100, https://doi.org/10.5194/egusphere-egu26-11100, 2026.