The expected alterations in nutrient levels and climate conditions are projected to significantly reduce oxygen concentrations in numerous stratified lakes globally. Nevertheless, the exact duration, timing, and consequences on lake oxygen over decadal to centennial scales remain uncertain due to the limited availability of long-term monitoring data. In this study, we introduce an innovative model-data assimilation approach that integrates 150 years of limnological and paleolimnological data to assess the human-induced impact and future outlook of dissolved oxygen (DO) conditions in the renowned Lake Geneva under various climate scenarios. Pluri-decadal series of limnological data monthly collected by the French Observatoire des LAcs (OLA database) were used to calibrate and validate the model. In addition, model outputs were further validated with published paleolimnological records for the past 170 years. Results of the calibration procedure show that the GLM-AED2 model accurately predicts the magnitude and seasonal dynamics of the state variables with goodness-of-fit metrics under the literature range (e.g. RMSE = 0.96 mg L^–1 and RRMSE = 25% for dissolved oxygen; RMSE = 6.53 ug L^–1 and RRMSE = 37% for chlorophyll-a, both in the epilimnion). Our analysis reveals that over centennial timescales, it was eutrophication combined with reduced winter mixing that initiated prolonged and severe bottom-water hypoxia. Conversely, examining the recent years and projecting forward to 2100, climate change is poised to be the primary driver of hypoxia in Lake Geneva and analogous lakes, even with decreased phosphorus concentrations. Our results strongly advocate for the necessity of reducing local phosphorus inputs in stratified lakes to avert deoxygenation. However, it is essential to acknowledge that doing so may also limit lake productivity due to nutrient availability.

How to cite: Jenny, J.-P., Soares, L. M. V., Mazure, T., and Desgué-Itier, O.: Unraveling Temporal Complexities in Lake Science through Sediment Records and Process-Based Models , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20515, https://doi.org/10.5194/egusphere-egu24-20515, 2024.

Detailed reconstructions of Quaternary paleoclimate and paleoenviromental evolution of the Canary Islands have been hampered by the scarcity of long terrestrial records.  In this study, we present the results of a multiproxy approach based on sedimentological, geochemical, and magnetic susceptibility measurements in a > 40 m long new sediment cores retrieved from a paleolake located within the Vega Lagunera valley on La Laguna, Tenerife Island (Canary Archipelago). Vega Lagunera is a NE-SW oriented valley formed by fluvial erosion of the Miocene basalts of the Anaga massif and blocked by Late Pliocene and Pleistocene lavas emitted from the NE Dorsal Ridge. The 40 m long sequence represents the longest Quaternary terrestrial record in the Canary Islands. Preliminary sedimentation rates based on OSL dates in previous cores suggest a basal date of > 400 ka and a 9 m long Holocene record. The geochemical and magnetic susceptibility signatures identified a shallow lake with clastic alluvial influences during the Pleistocene, a rapid Holocene onset and dominant shallow lacustrine sedimentation since mid Holocene till drainage of the remnant lake in mid 19^th century. The interplay of alluvial and lacustrine facies throughout the Holocene period and the geochemical evolution characterized the sedimentological processes linking lake and catchment dynamics, organic productivity, nutrient supply, and runoff. Age models are in progress to identify the glacial / interglacial evolution of these oceanic islands and the relative role of subtropical and mid latitude atmospheric and oceanic patterns.
This research is conducted as a part of the CCR-CAN project (TED2021-129695A-I00) supported by MCIN/AEI /10.13039/501100011033 and NextGenerationEU/ PRTR.

How to cite: Jambrina-Enríquez, M., Armenteros-Armenteros, I., Martín-Luis, M. C., Casillas-Ruiz, R., and Valero-Garcés, B. L.: A new > 400 ka paleoenvironmental and paleoclimate record from Tenerife Island (Canary Archipelago), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11700, https://doi.org/10.5194/egusphere-egu24-11700, 2024.

Short-term hydrological monitoring has limited our understanding of how climate and human activities affect flood erosion and deposition. Here, we reconstruct a 1000-year-long extreme flooding record by analyzing drill cores from the Daling River estuary (NE China), NE Asia, based on the observation that instrumental floods normally cause coarse particle enrichment in the estuary. Our data reveal that (1) centennial-scale climate aridification coupled with vegetation coverage reduction has enhanced flood erosion and estuarine sedimentation; (2) accelerated reservoir construction and reforestation and grass planting since 1960 have consistently reduced sediment flux and coarse particles reaching the estuary. Our findings promote our understanding of basinal erosion and estuarine sedimentation under climate aridification and human pressure.

How to cite: Sun, S., Dong, X., Nie, Y., Li, Y., Zhu, L., Cao, X., Ma, H., Li, Y., Wang, H., Hu, K., and Lu, Y.: A 1000-year extreme flooding record from NE Asia reveals the roles of climatic and anthropogenic changes in driving basin erosion and sedimentation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3739, https://doi.org/10.5194/egusphere-egu24-3739, 2024.

The second largest rainforest biome on Earth lies in the Congo Basin of central Africa. Due to increasing pressure associated with slash-and-burn farming practices as well as climate change, the rainforest may loose its ability to absorb atmospheric carbon. Interestingly, former studies have found evidence for a similar so-called “African Rainforest Crisis” that took place in the late Holocene, around 3000 years ago (Brncic et al. 2009; Garcin et al. 2018). There are some indications that this crisis was caused by the expansion of the Bantu people, who are believed to have migrated to this area to pursue extensive farming at this time. Pollen records, to the contrary, suggest a shift towards a drier climate as the primary mechanism inducing the crisis. Since data from this area are scarce, more information is needed to resolve the exact causes of the African Rainforest Crisis, especially since it is a likely analog for ongoing and future rainforest contraction.

To provide such information, we collected a total of about 30 m of core from 13 lakes along the rainforest-savannah boundary in the Kasaï Basin, Democratic Republic of Congo, which constitutes the southwest portion of the Congo Basin. We developed preliminary age models of the sediment records using bulk radiocarbon measurements to compare the estimated sedimentation rates. Two periods of reduced sedimentation rates around 700 and 3500 years before present have been identified. These can indicate the timing and spatial extent of erosive events usually linked to drying and a shift in vegetation. In parallel, we analyse the catchment’s vegetation through time using stable-carbon istopes to distinguish between the abundance of C₃ and C₄ plants. Additionally, bulk XRF and XRD data offers insights into the underlying mineralogy. First results suggest kaolinitic and quartz-rich sediments, indicating high wethering intensity. By using mineralogy as an indicator of weathering intensity, we expect to draw conclusions on the hydrology and temperature throughout the late Holocene. To further constrain the paleoclimate reconstructions, triple-oxygen isotope analysis on the clay-size fraction and pollen and charcoal analyses are planned. A holistic interpretation will aim to reveal the role of climate vs. land-use change as a trigger of the African Rainforest Crisis, which serves as an analog to better predict how the Congo rainforest will respond to today’s land use- and climate-triggered challenges.

REFERENCES

Brncic, T. M. et al. (2009) Holocene 19, 79–89.

Garcin, Y. et al. (2018) PNAS 115, 3261–3266.

How to cite: Engelhardt, M., De Clippele, A., Ludjwera, A., Haghipour, N., Six, J., Drake, T., De Groot, L., Van Oost, K., and Hemingway, J.: Lake archives from tropical Africa: Reconstructing the paleoclimate leading to the African Rainforest Crisis 3000 years ago, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7760, https://doi.org/10.5194/egusphere-egu24-7760, 2024.

Although about 98% of the Antarctic continent is covered by an ice sheet, seasonal lakes and small streams resulting from ice and snow melting are formed during the Austral summer. These ice-free areas, mainly located in coastal sites, provide a fertile environment for the development of microbial life. Isolation and extreme conditions in terms of light, temperature and nutrient availability generate peculiar ecosystems in the lake waters, characterized mainly by the presence of planktonic and/or benthonic microorganisms, especially cyanobacteria and microalgae. The water budget of coastal lakes is regulated only by melting and evaporation/sublimation, so that the organic matter from the catchment and the lake biomass is buried in sediments, which therefore represent a precious archive for the study of seasonal and interannual changes in the hydrology and primary productivity of the lakes. The high sensitivity of these environments to local climatic shifts is key to understanding how deglaciated areas may respond to larger scale changes. The lakes considered in this proposal are all located close to Terra Nova Bay, in the vicinity of the Italian research station Mario Zucchelli. Sediment samples from the same lakes were collected repeatedly in the period from 1990 to 2014 in the framework of the Italian National Antarctic Research Program (PNRA). So far, no study was ever performed on the temporal evolution of the lakes. The sediment samples analyzed here make up a 25-year long series that would encompass medium-term changes in the ecologic conditions of such sensitive environments. Samples were made available by the Antarctic Environmental Specimen Bank (BCAA, University of Genoa), associated to the Italian Antarctic National Museum.

Macroscopic changes were observed in coastal lakes in Northern Victoria Land over the last few years, regarding their extension that exhibited an overall decreasing trend that found no explanation yet. Organic markers buried in sediments could help identifying the factors that are driving the observed transformations and evaluating the sensitivity of these ecosystems to future change. Here, we investigate changes in the lipid composition through untargeted and targeted analysis of apolar and polar lipids using GC-MS and UHPLC-HR-MS/MS.

In order to complete the information gathered through the characterization of lipids, the study of nutrient availability, here performed through the detection of e.g. zinc ions in the range of 0.1-2 ppm using a paper-based printed electrochemical sensor and a miniaturized 3D printed extraction system for soil analysis, to understand if a correlation exists between the variation of nutrient content and lipid biomarkers and small to large-scale changes.

How to cite: Argiriadis, E., Sorarù, L., Colozza, N., Giannelli Moneta, B., Arduini, F., Cavaliere, C., and Vecchiato, M.: Multidecadal characterization of biogenic compounds and nutrients in Antarctic ice-free coastal lake sediments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16107, https://doi.org/10.5194/egusphere-egu24-16107, 2024.

Understanding how lake ecosystems respond to anthropogenic disturbances including mining, agriculture, deforestation, and more is often best answered with historical time series. Unfortunately, a lack of long-term monitoring data can make this difficult; paleolimnology offers an alternative, allowing for the reconstruction of past conditions using proxies from sediment records. As part of the nationally funded Canadian Lake Pulse Network, we analyzed sediment cores from 116 lakes across Canada using micro-X-ray fluorescence core-scanning (µXRF). µXRF served to generate abundance profiles for several elements (e.g., Ca, Sr, Ti, Pb, Cu, Zn), allowing for the assessment of spatiotemporal geochemical changes in Canadian lakes dating back to ~1850 AD. We calibrated µXRF core-scanning with conventional geochemical methods in a 48-lake subset and found strong correlations for numerous elements between conventional wet chemistry and µXRF-measured concentrations (Zilkey et al., accepted, Environmental Advances). We then assessed the temporal variability in sediment cores using constrained hierarchical cluster analysis and generalized additive models. Our preliminary results indicate that geochemical change demonstrates significant regional structure. On balance, lakes in eastern Canada predominantly demonstrated a temporal enrichment in metallic elements (e.g., Pb and Zn), while lakes in central and western Canada had a temporal enrichment of elements commonly associated with catchment erosion (e.g., Ti, Sr, K). Our results highlight the heterogeneity in responses across a vast landscape with diverse geological characteristics and land uses, and in the relative importance of anthropogenic disturbances shaping lake sediment geochemistry over time. Key next steps include the investigation of lakes that are distinct relative to their regional trends and the local environmental factors that might explain their contrasting response.

How to cite: Zilkey, D. R., Jenny, J.-P., Baud, A., Francus, P., Antoniades, D., and Gregory-Eaves, I.: Canadian lakes are changing in response to anthropogenic disturbances: a Pan-Canadian geochemical study using micro-X-ray fluorescence sediment core-scanning., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16100, https://doi.org/10.5194/egusphere-egu24-16100, 2024.

The brGDGT-based ratio MBT’_5ME has been widely used in soil (1) and lake (2) systems globally to estimate changes in mean annual temperature over time. Despite the development of numerous lake-specific calibrations (3, 4), a substantial residual error (2.0-2.7 ℃) remains in temperature calibrations, suggesting the potential influence of confounding factors other than temperature on the paleothermometer MBT’_5ME. Investigating changes in brGDGT distribution over both shorter (seasonal water column) and longer (last 14 ka) time scales within a single lake system has provided significant novel insights for the application of MBT’_5ME in lacustrine systems.

Analyzing a dataset of lake sediment samples (n= 95) spanning three distinct climate periods: the Glacial interstadial, Younger Dryas, and Holocene, variations in brGDGTs with time within a prealpine lake sediment core offered valuable insights into the lake's environmental history and the interdependencies of brGDGTs. Within the Holocene,  the higher fractional abundance of brGDGT Ia is interpreted as driven by stronger thermal water column stratification, especially in the early Holocene (11.7-7.4 cal. ka BP) . Furthermore, the provenance and environmental drivers of the sedimentary brGDGTs were identified by comparing sediment samples to the lake's seasonal particulate matter (SPM) samples (n= 20). Although hypolimnion brGDGT isomer ratio (IR) was characterized as a function of dissolved oxygen in the lake’s SPM, only a muted influence from seasonal or permanent lake water anoxia was observed on the sedimentary brGDGTs isomer ratio (IR), and the IR is instead proposed as a secondary proxy for temperature.

While Lake Rot’s epilimnion showed a dependency between MBT’_5ME and temperature (and lack of hypolimnion’s MBT’_5ME dependency on temperature), the concentration changes and interdependencies of brGDGTs during the oligotrophic phase of the lake mimicked the epilimnion conditions. This suggests that coring at the oxic depth of (seasonally) anoxic lakes can prove successful for using MBT’_5ME as a lake surface paleothermometer. The presence of brGDGT Ia, commonly associated with thermally stratified surface summer water, reinforced this observation, and suggests that the temperature proxy is primarily linked to thermal stratification rather than single influence of mean annual temperature. These findings have substantial implications for paleoclimate studies. It is evident that the development of seasonal stratification plays a crucial role in influencing MBT'_5ME values. Consequently, MBT’_5ME mainly reflects summer warmings in Lake Rot during early Holocene and colder summer temperatures for late Holocene. Finally, with minimum impact from lake’s XRF-based anoxia history, brGDGTs isomer ratio (IR), shows a strong potential to be employed as a mean annual temperature proxy.

1: Crampton-Flood et al., (2020). Geochimica et Cosmochimica Acta, 268, 142-159

2: Stefanescu et al., (2021). Organic Geochemistry, 152, 104174

3: Martínez-Sosa et al., (2021). Geochimica et Cosmochimica Acta, 305, 87-105

4: Raberg et al., (2021). Biogeosciences, 18(12), 3579-3603

How to cite: Ajallooeian, F., Ladd, S. N., Dubois, N., Lever, M. A., Schubert, C. J., and De Jonge, C.: brGDGT paleothermometer MBT’5ME as a novel diagnostic tool to detect thermal stratification in lakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5860, https://doi.org/10.5194/egusphere-egu24-5860, 2024.

The carbon dynamics of lacustrine deposits play an important role in controlling the atmospheric carbon cycle. However, the influences of various sedimentary factors on carbon accumulation in lacustrine deposits are rarely known. In this study, the petrological and geochemistry analyses of organic-rich (average total organic content = 24.22 wt.%) lacustrine deposits and organic-poor (average total organic content = 2.48 wt.%) lacustrine deposits buried under a peatland (the Zhibian peatland) in Northeast Asia are used to explore the above issues. Results suggest that the concentrations of major oxides, trace elements and rare earth elements in the organic-poor lacustrine deposits are higher than those in the organic-rich lacustrine deposits. Furthermore, these lacustrine deposits were sourced from felsic rocks. The tectonic background was continental island arc and active continental margin. Additionally, the sedimentary models of lacustrine deposits buried under peat sequence were also concluded. Organic-poor lacustrine deposits were developed in a deep-water area, that was freshwater and oxygenic condition. This type of lacustrine deposit was influenced by the frequent input of coarse-grained terrigenous debris and low productivity. In contrast, the organic-rich lacustrine deposits were developed in a shallow-water area, that was saline and anaerobic condition. This type of lacustrine deposit was influenced by a rare input of fine-grained terrigenous debris and high productivity. These findings should assist future studies on the carbon dynamics of buried lacustrine deposits. This study would provide a representative example of carbon accumulation processes and mechanisms in buried paleolake system in Northeast China.

How to cite: Zhang, M.: The influences of sedimentary environments on carbon accumulation in lacustrine deposits: Evidences from elemental geochemistry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3687, https://doi.org/10.5194/egusphere-egu24-3687, 2024.

Located in the south-west Pacific, New Caledonia is an archipelago with a complex geodynamic history. Grande Terre, the main island, is covered by more than 25% of regolith developed on ultramafic rocks. These peridotites, naturally enriched in metallic elements (Fe, Al, Ni, Co, Cr), constitute most of the southern part of New Caledonia. Since approximately 27 Ma, these rocks have undergone weathering (under a humid tropical climate) and erosion. This combination has led to the formation of the fluvio-lacustrine system, by accumulation of sediments eroded from local summits in depressions and valleys.

The distribution of the fossil fluvio-lacustrine system in New Caledonia has been mapped by Folcher N. (2016). The sedimentary filling of this system is essentially of fluvial origin, with rare lacustrine occurrences. Its structure is complex and some sedimentary levels show abnormally high accumulations of Trace Metallic Elements (Ni, Co, Cr). Thus, the METAL FLAP thesis project aims to understand how the geodynamic history, paleoenvironmental evolution, and diagenetic processes within the fluvio lacustrine formation influence the dynamics of metallic elements and their potential transfer to the modern fluviatile system?

In one of the sub-basins of the system (the basin of the pirogue river), the relationships between geochemistry and structures have been studied at the edges of two types of objects: horizontal indurated beds and vertical ferruginous partitions. The first results suggest that these two types of structures, which have different formation origins, strongly impact the distribution of elements in sediments (enrichment in Cr, depletion in Fe, etc.). The vertical partitions are thought to be related to fluid circulation in basin fractures, while the formation of horizontal indurated layers is believed to originate from fluctuations in groundwater levels. The quantification of the contribution of each phenomenon to the dynamics of elements is still poorly defined but constitutes one of the major focuses of this study.

Furthermore, a detailed analysis of the system’s architecture and a thorough sediment characterization, coupled with the study of the few fossils present in the formation, shed light on the paleoenvironmental history of the region during deposition. This also provides assistance in understanding the geological processes affecting the formation of the fluvio-lacustrine system, as well as the dynamics of metallic elements in the land-sea continuum. This fossil continental system in the southern region is one of the least studied formations in the area, despite the wealth of information it holds about the geodynamic history of New Caledonia during the last post-obduction cycle.

How to cite: Parmentier, J.-B., Pattier, F., Mathian, M., Gaullier, V., Gunkel-Grillon, P., Maurizot, P., Tribovillard, N., Marchand, C., Cohen, O., Blaise, E., Zanella, A., and Devillers, N.: Fossil Fluvio-Lacustrine System of the Southern Grande Terre of New Caledonia : Paleo-environmental Archives and Dynamics of Trace METALlic Elements (TME), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22570, https://doi.org/10.5194/egusphere-egu24-22570, 2024.

Lake Van in Eastern Anatolia (Turkey) is the world's largest alkaline lake and the fourth largest terminal lake. A long, almost continuous, and partly annually laminated sedimentary profile, recovered during the ICDP PALEOVAN campaign in 2010 provided valuable information about the climatic, vegetation, tectonic, and volcanic history of the region over the last ca. 600 ka (Litt & Anselmetti 2014 and references therein). Individual proxy records suggest that Lake Van and its vicinity experienced significant hydroclimatic changes in concert with glacial/interglacial cycles and Dansgaard/Oeschger oscillations. The results of the original PALEOVAN project constituted an excellent framework and motivated further problem-oriented research. The last 10 years have seen a number of inspiring publications testing strengths and limitations of carbonate-based proxies in lakes and deepening our understanding of forcing mechanisms and rates of ecological changes.

Here we summarise the highlights of Lake Van research to date and offer a perspective on exciting ongoing work. Systematic analyses of the sedimentary carbonate inventory of Lake Van put the mineralogy of lacustrine carbonates in the limelight and revealed caveats of geochemical analyses on bulk samples (McCormack et al., 2018, 2019). Moreover, these studies stretched the envelope of dolomite-forming environments and early diagenetic products (McCormack & Kwiecien, 2021; McCormack et al., 2023). The established climatic context (Pickarski et al., 2015a, 2015b) and annually laminated nature of Lake Van sediments enabled the quantitative estimation of the time vegetation takes to recover after volcanic eruptions and elucidated the effect tephra deposition has on in-lake productivity (Pickarski et al., 2023).  Lake Van sediments keep on giving, with ongoing projects targeting the timing and mechanism of the lake closure and high-resolution comparisons of the impact of interglacial warming on (pan)regional hydroclimate. So perhaps 'The Best Of' is yet to come!

References

Litt & Anselmetti 2014. Lake Van deep drilling project PALEOVAN. Quaternary Science Reviews

McCormack & Kwiecien, 2021. Coeval primary and diagenetic carbonates in lacustrine sediments challenge palaeoclimate interpretations. Scientific Reports

McCormack, et al., 2019. Refining the interpretation of lacustrine carbonate isotope records: Implications of the mineralogy-specific Lake Van case study. Chemical Geology

McCormack et al., 2018. Controls on cyclic formation of Quaternary early diagenetic dolomite. Geophysical Research Letters

McCormack, et al., 2023. Hydrochemical mixing‐zones trigger dolomite formation in an alkaline lake. Sedimentology.

Pickarski et al., 2023. Volcanic impact on terrestrial and aquatic ecosystems in the Eastern          Mediterranean, Communications Earth & Environment

Pickarski et al., 2015b. Vegetation and environmental changes during the last interglacial in eastern Anatolia (Turkey): a new high-resolution pollen record from Lake Van. Palaeogeography, Palaeoclimatology, Palaeoecology

Pickarski et al., 2015a. Abrupt climate variability of eastern Anatolia vegetation during the last glacial. Climate of the Past

How to cite: Kwiecien, O., McCormack, J., Pickarski, N., Bontogniali, T. R. R., Baldermann, A., Yue, J., and Litt, T.: So Far... The Best Of Lake Van, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15977, https://doi.org/10.5194/egusphere-egu24-15977, 2024.

Lacustrine sediment sequences can provide long and complete records of earthquake recurrence patterns due to their continuous nature of subaqueous sedimentation. This gives this “natural seismograph” a high sensitivity for registration of seismic shaking and accurate age-depth control, these characteristics are important parameters for high-quality seismic hazard assessments. As the middle strand of the North Anatolian Fault (MNAF) is a slow slipping fault (5 mm/yr), a long-term earthquake chronicle is required to study its behavior. Here, we report on findings from three long sediment cores (from 8.5 to 15 m), retrieved in Lake Iznik (northwest Türkiye), crossing the Iznik underwater fault, that provide insight into the local and regional earthquake cycle and thus improve the paleoseismic history for the NAF system over the last 8000 years. We used radiocarbon-based age-depth models combined with sedimentological observations, X-ray fluorescence elemental data, and seismic reflection data to reconstruct the spatiotemporal rupture variability. Recurring millimetric, coarse-grained laminae identified as event deposits were deposited synchronously at the three coring sites. Over the last 2000 years, the ages of the event deposits recorded in Lake Iznik correspond to the historical evidence of seismic activity reported along the North Anatolian Fault (NAF) system, allowing us to recognize regional earthquake-triggering mechanisms and assess seismic intervals. The event deposits are inferred to be earthquake-triggered, and the sensitivity to earthquake shaking in Lake Iznik is proportional to the sedimentation rate. Our record demonstrates that Lake Iznik has been repeatedly exposed to significant seismic shaking over the past 8000 years. Our data suggest that large earthquakes with moment magnitudes Mw >7 occur on the Iznik fault segment part of the MNAF with a mean recurrence interval of ~1000 years. At the regional scale period of seismic activity alternates with several hundred years of quiescence. This study allows us to investigate the timing of large paleoearthquakes over the last 8000 years, providing important input for seismic hazard assessment and increasing societal awareness and preparedness in the case of future catastrophic events along the MNAF.

How to cite: Duarte, E., Sabatier, P., De Sigoyer, J., Gastineau, R., Anselmetti, F. S., Rapuc, W., Fabbri, S. C., Domenge, J., Şahin, M., and Gündüz, S.: An 8000 yr lacustrine paleoseismic record (Lake Iznik, NW Türkiye): Implications for the seismic cycle of the Middle Strand of the North Anatolian Fault, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10699, https://doi.org/10.5194/egusphere-egu24-10699, 2024.

Assessing the hazard of extraordinary strong earthquakes in slowly deforming intraplate regions such as the European Alps is difficult, due to a lack of information on their occurrence. They are characterized by long recurrence intervals and identifying the source faults is difficult. However, on-fault evidence of a surface rupturing earthquake in the eastern Southern Alps was indicated by an archeoseismological study of Galadini and Galli (1999) in Egna (South Tyrol, Italy), which is in an area of low recent seismic activity. Displaced walls of a Roman Age building and paleoseismic trenches revealed the rupture of a NNE-SSW striking fault, which is dated to the 3^rd century CE. To test the hypothesis, this lacustrine paleoseismology study aims to find evidence of ground shaking in the sediments of Kleiner Montiggler See, a lake located only 10 km from the archeological site. Multiproxy analysis of sediment cores reveals an event layer at a depth between 64 and 69 cm below the lake floor. It is characterized by a sharp base, high density, grainsize oscillations within a normal grading trend, a high amount of detrital material and a decrease in organic matter, compared to the background sediment. After evaluating and finally excluding many possible processes that could have induced the deposit, it can be concluded that a seismic seiche caused bottom currents, resuspending sediment and eroding material from the shore that finally got deposited as an outstanding event deposit in the deeper parts of the basin. According to our ¹⁴C based age-depth model, the event layer occurred between 8 and 450 years CE (95% probability range; mean age 222 CE), therefore supporting the hypothesis of the Roman Age surface rupture at the Egna site. This is the only event of this type recorded in the lake sediments of Kleiner Montiggler See in the last ~5000 years.  A minimum macroseismic intensity (EMS-98) of VII at the lake was estimated for the ground motion caused by the Egna fault rupture. This was done by investigating the sedimentological characteristics of the event layer, as well as considering negative evidence for other large, historical earthquakes and possible long-term catchment response recorded in the sediments. By applying an intensity prediction equation, a minimum estimated magnitude (M_i) of 6.2 ± 0.5 was derived. Due to negative evidence in Lake Ledro (63 km SW of Egna) at this timing, a maximum magnitude of 6.0 ± 0.5 was estimated. Therefore, we conclude that the magnitude of this event was most likely between 5.7 and 6.5. This study indicates that extraordinary strong and thus hazardous earthquakes can occur in areas of low recent seismic activity. It therefore provides important information for improving seismic hazard assessment and the estimation of the maximum credible earthquake in South Tyrol.

How to cite: Niederstätter, M., Strasser, M., Ramisch, A., and Moernaut, J.: Limnogeological investigations of the Montiggler Seen (South Tyrol, Italy) reveal paleoshaking evidence caused by surface rupturing earthquake in the Southern European Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-81, https://doi.org/10.5194/egusphere-egu24-81, 2024.

Located in Massif Central (Ardèche, Auvergne-Rhône-Alpes, France), Lake Issarlès experienced since 1954 decametric lake level changes due to EDF water management. It has been hypothesized in several endoreic and maar lakes that lake level fluctuations can increase the recurrence of mass movement deposits (MMDs) because of their steep slopes (Kliem et al., 2013). The deep basin of the maar Lake Issarlès is filled by several meters of MMDs clearly visible in seismic reflection surveys and sediment cores. Here, we present results from a multiproxy study (geophysics, radiography, XRF, radionuclides & radiocarbon dating) that investigates the potential of Lake Issarlès as a paleo-seismological recorder (Defive et al., 2023).

Derived from a geophysical survey using a 4 kHz from Knudsen in June 2019 (five months before Le Teil earthquake; see details below) a coring campaign was conducted in 2020 from an anchored platform in the central deep basin, together with a new seismic reflection survey using high-resolution sub-bottom profiler Echoes 10 000. Acoustic sub-bottom data highlight several MMDs in the central basin and at the bottom of slopes, and a recent thin reflector close to the water-sediment interface. At about 7 meters in sediments, a metric sized MMD prevents deeper acoustic penetration. The 7 m-long composite sequence, documented by radiography, geochemistry, radiocarbon, radionuclides and “varves” counting, consists of laminated sediment interrupted by rapidly deposited layers such as clayey layers, MMDs, slumps and turbidites. The first event could be linked to the recent damaging M_w 4.9 (M_Lv 5.4) earthquake that occurred on November 11^th, 2019 in Le Teil village, 60 km east from Lake Issarlès. Another event is contemporaneous with the installation of underground pipes between 1947 and 1953 by EDF, and two events are synchronous with regional historical earthquakes occurred at Tricastin in 1934 & 1873 (M_Lv ~7) (20 km south of Le Teil).

The whole sequence reaches back to 6000 years (radiocarbon dating) and delivers at least ten main events. Four main sedimentary units are derived from (1) the recurrence of MMDs visible in the sediment cores & the seismic profiles, (2) the dynamic of the main driver PC1 of the Principal Component Analyses of XRF data as well as the inc/coh ratio fluctuations, which is a proxy of organic matter content (Jouve et al., 2013; Guyard et al, 2007). Changes in sedimentation rates and sedimentary dynamics extracted from this multiproxy study suggests the lake sensitivity to record paleoearthquakes may have fluctuate through time and that the magnitude of past events cannot be extrapolated from the size or volume of the MMDs.

Kliem et al. (2013b) Quaternary Science Reviews 71, 131–146.

Defive et al. (2023) Quaternaire 34(2), 93-122

Jouve et al. (2013) Quaternary Science Reviews 71, 191-204

Guyard et al. (2007) Quaternary Science Reviews 26, 2644-2660

Chapron et al. (2022) Quaternary International 636, 134-153

How to cite: Jouve, G., Chapron, E., Chassiot, L., Foucher, A., Raynal, J.-P., and Defive, E.: Mid-to-Late Holocene history of mass movement deposits at maar Lake Issarlès (Ardèche, France): a paleosismological record ?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-321, https://doi.org/10.5194/egusphere-egu24-321, 2024.

South-Central Chile is a geodynamically very active area that experiences great subduction megathrust earthquakes, mass-wasting processes and frequent volcanic eruptions. These processes can induce sudden landscape changes that leave long-lasting geomorphological and sedimentary traces. They can also lead to significant lake level rise, but evidence for this is exclusively found under water and hardly investigated. Lago Llanquihue (41.156°S; 72.816°W) is a large and deep (40 x 40 km; 317 m deep) piedmont lake at the western foot of the Andes, and forms an important touristic hotspot. Its current outflow is at the western edge and its small catchment is dominated by two active volcanoes: Osorno and Calbuco. Based on previous geomorphological studies in the 1960-70s, it was hypothesized that the lake level of Lago Llanquihue was much lower during most of the Holocene and rose to its present level only in the Late Holocene. According to the hypothesis, lahars and/or lava flows in the late Holocene dammed the outflow in the eastern part of the lake system leading to lake level rise and subsequent drainage towards the west through the frontal moraine belts.

In this study, we aim to test and constrain this hypothesis by investigating the submerged geomorphological features and sedimentation patterns in Lago Llanquihue. We complement this data by a sedimentary study of Laguna La Poza, a small lake (1.7 x 0.2 km; 6 m deep) in a fluvial valley that is believed to have been inundated by the Late-Holocene lake level rise. Seismic-stratigraphic analysis of Lago Llanquihue reveals submerged lake level terraces (ca. 35-55 m water depth) of which individual levels can be traced in different parts of the lake. These terraces are constituted of erosional unconformities and delta topset geometries, and are covered only by a thin (0.5-3 m) drape of lacustrine sediments. Short sediment cores show different lithologies below these unconformities: fine-grained grey laminated sediments with dropstones, or coarse sand with shell fragments. These are interpreted as glaciolacustrine sediments from Late Glacial times and as sandy beach environments, respectively. Additionally, Laguna La Poza shows a significant change in sedimentation at about 1 m depth, where a laterally-variable fining-upwards medium sand to gravel unit with pronounced cross-stratification is covered by horizontally-stratified fine-grained organic-rich lake sediments. We interpret this sequence as evidence for a sudden inundation of a fluvial valley by a rising Lago Llanquihue. Given the rather thin drape of lake sediments over the unconformity (Llanquihue) and fluvial sediments (La Poza), a Late Holocene timing of lake level rise is plausible. Current investigations aim at correlating both lacustrine sedimentary records by geochemical analysis of tephra marker layers and use ¹⁴C dating to constrain the timing of the sudden lake level rise.

How to cite: Benischke, S., Thomaser, S., Wils, K., Molenaar, A., Moreno Allende, V., Haas, J. N., Melnick, D., De Batist, M., Strasser, M., Konzett, J., Urrutia, R., and Moernaut, J.: A drastic Late-Holocene lake level rise of Lago Llanquihue, Chile´s second largest lake , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1672, https://doi.org/10.5194/egusphere-egu24-1672, 2024.

Cryptotephra research has emerged as a major tool for determination of the age of sediments and unraveling the relationship between past volcanic events and their environmental impacts. Lacustrine deposits are particularly important for continental tephra research. Lakes provide relatively stable environments conducive to the long-term preservation of (crypto)tephra layers, forming valuable continental cryptotephra archives. While studies on fingerprinting of marine tephras and peat samples are more common, the identification and quantification of cryptotephra within lacustrine records remains an underexplored area.    
In this study, we introduce innovative workflows for the quantification of cryptotephra, particularly in lake sediments with distant Laacher See tephra fallout, which represents the most important stratigraphic marker in late-glacial deposits in Central Europe. Our approach initiates with the identification of potential cryptotephra positions and thickness of the deposits, accomplished through the integration of magnetic susceptibility (MS), X-ray fluorescence (XRF), and computer tomography (medical- and micro-CT) to precisely delineate the extent of the cryptotephra layer within the sediments. The subsequent step evaluates presence and identifies the source of the present cryptotephra layer. This is accomplished using scanning electron microscopy (SEM) and polarizing microscopy to visually confirm the presence of cryptotephra and investigate its geochemical fingerprint, enabling linkage to a specific volcanic eruption.    
The key element of our study are methods for quantifying cryptotephra glass shards within sedimentary records. Shard extraction using stepwise flotation with heavy liquids and quantification using standardized markers and a polarizing microscope provides a robust, straightforward laboratory-based technique. Additionally, we offer an innovative, software-based alternative that combines TIMA analysis on thin sections with customized image analysis to study the area fraction of the glass phase, its depth-dependent variation, particle density with a focus on clustering behavior, depth-dependent particle count, total particle count, and particle size distribution within the glass phase.    
The significance of both methods lies in the efficiency and precision of cryptotephra quantification, enabling a deeper understanding of shard concentration, depth-dependent shard distribution, as well as multi-site comparison of shard influx within continental cryptotephra deposits.

How to cite: Meier, V., Hrstka, T., Ohser, J., Brandstätter, B., Kletetschka, G., and Vondrák, D.: Cryptotephra quantification in lake sediments: Two workflows developed for sites with distant Laacher See tephra fallout, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4368, https://doi.org/10.5194/egusphere-egu24-4368, 2024.

The Tibetan Plateau formation, resulting from the collision between India and Eurasia, is accompanied by significant seismic activity. Along its SE margin, the sinistral Xianshuihe fault is one of the most active faults in China. To understand the seismic cycle and estimate subsequent hazards, long-term records extending beyond historical archives are required. In Kangding's restraining bend, fault partitioning leads to seismic activity being distributed across four branches, exposing significant population and critical infrastructures to seismic hazards. To document the long-term patterns of fault activity, we identified seismically-triggered event deposits in three mountain lakes near the fault, using a multiproxy approach, including CT scanning, grain-size analysis, and XRF core scanning, associated with chronology based on palaeomagnetism, short-lived radionuclides, and radiocarbon ages. Our investigation across three sites (Yari Acuo, Yalatuo, Mugecuo) distributed over 30 km of the fault, revealed varying sensitivities to seismic events over the past ~300 years. Based on these different sensitivities to record earthquakes, this multi-site approach allowed us to relocate historical earthquakes based on sediment core evidence. However, the high frequency of events and the uncertainties in age models limit our ability to unambiguously attribute the oldest deposits to specific events. The recently retrieved 3.6 m-long core from Lake Yalatuo, on which we will apply similar analyses, appears more promising to reconstruct the long-term regional palaeoseismological record and discuss the Xianshuihe fault seismic cycle.

How to cite: lemot, F., Sabatier, P., Chevalier, M.-L., Crouzet, C., Rioual, P., Develle, A.-L., Fang, Z., and Replumaz, A.: A lacustrine sediment perspective on the seismic cycle in Southeast Tibet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5762, https://doi.org/10.5194/egusphere-egu24-5762, 2024.

Lacustrine settings constitute a unique environment that preserves detailed expressions of allocyclic signals such as those of climate and tectonics. Possible decryption of these signatures may stem from careful scrutiny of the sedimentation dynamics (temporary base-level variations), lake-level fluctuations (accommodation), and resulting strata bounding surfaces that are used to build a conventional sequence stratigraphic framework. The present work deals with this challenge and provides insights from a case study where lacustrine sedimentation occurs onto a tectonically active reverse drag associated with normal faulting within a key climate region (Lake Ifrah, Northwest Africa). Moreover, we investigated soft-sediment deformation structures (SSDSs) within Lake Ifrah sediments, which can be good proxies for neotectonic and paleoseismic activities. We analyzed both brittle and liquidization-induced SSDSs, including load structures, water-escape structures, shrinkage cracks, subsidiary grabens, and bed-parallel slips. Up to five facies models (accounting for lithological domination, wind-driven energy, and lake-level state) and three lowest rank T-R sequences, deposited since the Marine Isotope Stage-3 (MIS-3), have been identified. Periods with sustained high lake levels appear to be mainly precession-paced (as during MIS-3 and the Early Holocene). Furthermore, sedimentation dynamics are shown to probably respond to millennial timescale climate variability associated with North Atlantic cooling events (Dansgaard-Oeschger stadials, Heinrich events) and, interestingly, to enhanced Saharan winds during the deglacial period. On the other hand, tectonism had a rather instantaneous effect on lake level and sedimentation. Two tectonic pulses marking instantaneous differential hanging-wall subsidence have triggered a sharp drop in relative lake level, hence conditioning a forced regression. Facies analysis and deformation-trigger assessment helped to discern endogenic from exogenic triggers, with seismic activity inferred as a primary cause for liquidization-induced deformations.

How to cite: Azennoud, K., Baali, A., and Ait Brahim, Y.: Imprints of climate and neotectonic activity in lake sediments developed upon a reverse drag (Lake Ifrah, NW Africa): Integration of detailed sedimentological and sequence stratigraphic approaches., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-695, https://doi.org/10.5194/egusphere-egu24-695, 2024.

Western Antarctic Ice Sheet (WAIS) grounded below sea level is experiencing rapid basal melting and is known to have undergone complete ice sheet collapse in the past. We investigate Si and Sr isotopic signatures of marine porewater and sediment from an 800-meter-long sediment core (U1532) dating back to late-Miocene (5.7 Ma) from Amundsen Sea, retrieved as a part of IODP Expedition 379. The present work explores porewater and sediment geochemical and isotopic signatures to understand marine silicate alterations and to link sedimentary signatures to glacial-interglacial dynamics of WAIS.

The sediment lithology is dominated by silty clay, dispersed with biogenic silica and ice rafted debris (IRD). The depositional environment receives high supply of terrigenous sediments during glacial times, transported by advancing WAIS towards shelf edge, evident from high sedimentation rates (upto 61 cm/kyr) and occurrence of terrestrially derived kaolinite clays. The bulk ⁸⁷Sr/⁸⁶Sr of sediments shows an overall increasing trend with depth, ranging from 0.7095 to 0.7225. Interestingly, porewater shows a steady increase in Sr concentration with depth (from 90 to 320 μM), except the deepest strata between 660 to 760 meter bsf, where we observe a slight decrease. The pore water ⁸⁷Sr/⁸⁶Sr signatures fluctuate between 0.7084 to 0.7101, with two phases of low ⁸⁷Sr/⁸⁶Sr ratio and three phases of higher ⁸⁷Sr/⁸⁶Sr ratio than contemporaneous seawater. The interaction of fluids with more radiogenic Sr rich glacigenic detrital phases can explain observed increasing phases of pore water ⁸⁷Sr/⁸⁶Sr signatures. The more radiogenic ⁸⁷Sr/⁸⁶Sr source can be traced to subglacial erosion and weathering of lower Paleozoic/Mesozoic terranes of Western Antarctica, possibly transported through (paleo)ice stream systems into the Amundsen Sea. The sediments at distinct phases of low pore water ⁸⁷Sr/⁸⁶Sr coincides with Miocene-Pliocene transition and late Pliocene, likely resulting from basaltic alterations, associated with subglacial volcanic provinces of West Antarctic rift system.

The pore water dissolved silicon (DSi) and δ³⁰Si signatures results from a dynamic balance between dissolution of biogenic and reactive lithogenic phases, and formation of authigenic aluminosilicates. The DSi profile of pore water varies between 60 and 900 μM, exhibits three distinct phases of enriched DSi, associated with sediment intervals of abundant biosiliceous deposits (diatoms and radiolarians). Occurrence of IRD in these intervals points to a pelagic and hemipelagic sedimentation, associated with ice sheet retreat during warm interglacial periods. In order to distinguish possible sources of DSi to pore water, we employ a sequential leaching technique to separate major Si bearing phases from marine sediments. The biogenic silica associated with the Na₂CO₃ leach exhibits a higher Si/Al ratio (6 to 365) and a δ³⁰Si between 0.6 to 1.5‰, consistent with documented range of diatoms and radiolarians globally. The metal oxy-hydroxides and clay fractions represents lightest Si pool in marine sediments, with δ³⁰Si varying between -0.7 to -3.1‰, while lithogenic silica exhibits δ³⁰Si between -0.5 to 0.2‰. Through careful evaluation of pore water Si isotopic signatures, we will be able to link sediment supply of Si phases to past ice sheet dynamics of Western Antarctica.

How to cite: Pullyottum Kavil, S., Hong, W.-L., Huang, T.-H., Kim, J.-H., and Huang, K.-F.: Linking marine silicate alteration signatures in pore water to dynamics of Western Antarctic Ice sheet since late Miocene, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9331, https://doi.org/10.5194/egusphere-egu24-9331, 2024.

Huatung Basin, Gagua Ridge, Yaeyama Ridge, and Ryukyu Forearc Area are the main terrain characteristics offshore eastern Taiwan. Several submarine canyons are distributed in the basins and play an important role in sediment transportation. In terms of geographical location, Taiwan and Ryukyu Islands are the main sources of terrestrial materials, while Luzon Island, upstream of Kuroshio, is also one of the potential sources. Tectonic, typhoon, and monsoon activities intensively affect the flux of terrestrial materials into the ocean, which leads to the variation of sedimentation rates from 0.35 cm/a in the nearshore area of Taiwan to 0.06 cm/a in the Huatung Basin. All are much higher than the West Philippine Basin (5-7 mm/ka). Based on the differences in terrestrial material composition among Taiwan, Ryukyu, and Luzon, the study of clay mineral composition has become a potential tracer for identifying the source of sediments offshore eastern Taiwan. The controversy lies in the high content of smectite in the Huatung Basin. It was speculated that the main provenances of smectite may from eastern Taiwan (Chimei Igneous Complex) and the Ryukyu Island Arc, and the canyon systems developed off the eastern Taiwan transport terrestrial sediments over 150 km and deposited in deep Huatung Basin through turbidity currents or debris flows (Lin, 2021); or the Kuroshio transport the Luzon Arc materials into this area (Nayak et al., 2021). However, both interpretations are challenged by new comprehensive data. During the NOR1-0038A cruise in 2022, fist-sized pumice (~6 cm) was collected from the surface of the box core at the HT01 site in the Huatung Basin. Based on the mineral composition of the pumice, it is speculated that it was the product of the eruption of the submarine volcano "Fukutoku-Okanoba" in August 2020, and was brought here by currents and winds. This incident also had an impact on Taiwan's coast, with large amounts of pumice deposited in Taiwan's ports and beaches. The discovery of the "Fukutoku-Okanoba" pumice in the deep sea is of great significance to the source of volcanic ash or volcanic glass in sediments off eastern Taiwan. In addition, during the "Hakuho Maru" expedition from Dec. 13 to 23, 2023, large amounts of granite samples were first time collected by bottom dredge on the northern part of the Gagua Ridge, which may also be an important source of smectite. With the development of marine geological surveys in deep waters off ​​eastern Taiwan, our understanding of various sedimentary processes and sediment source-to-sink processes offshore eastern Taiwan continued to expand.

How to cite: Su, C.-C., Lin, J.-K., Hsu, T.-W., Chen, Y.-H., and Hsu, S.-T.: Distribution of clay minerals offshore eastern Taiwan: New evidence of volcanic material sources and transportation processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14931, https://doi.org/10.5194/egusphere-egu24-14931, 2024.

In Southwest Florida (SWFL) red tide (Karenia brevis) is a natural hazard and produces potent toxins, to both human and marine life, known as brevetoxins. Red tide, a microscopic alga species, is responsible for environmental, economic, and human health problems in this region. However, our understanding of natural and anthropogenic drivers of red tide are still poorly understood. This study endeavors to reconstruct brevtoxins records in marine sediments with the purpose to better understand present day blooms compared to historic red tide blooms in SWFL. This may be best achieved by looking at sediment cores from blue holes along the West Florida shelf. Blue Holes are natural geologic formations originating on land, as sink holes, which filled over time as global sea level rose. Generally, anoxic conditions found in blue holes provide excellent preservation of long geologic records and provide a unique opportunity to study brevetoxin as biomarkers in sediment cores. In 2023, sediment cores were collected from the Amber Jack Blue Hole off the coast of SWFL. The sediment cores were sliced at 1 cm intervals, and solvent extracted for the analysis of brevetoxins using a LC-MS/MS. The sediments were also analyzed for grain size analysis and scanned using x-ray. This study examines the vertical preservation depth of Karenia brevis and analyzes historic red tide events preserved within the Amber Jack blue hole sediments. This research provides the first opportunity to study red tide chemical biomarkers in high resolution blue hole sediment cores.

How to cite: Ruiz, A., Muller, J., Adhikari, P., Catasus, A., Donnelly, J., and Hengstum, P. J. V.: Brevetoxin Preservation in Marine Sediments from Amber Jack Blue Hole, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19071, https://doi.org/10.5194/egusphere-egu24-19071, 2024.