SSP3.2

The floodplains of the mighty river Ganga are centrally located in the Himalayan foreland basin and act as temporary storehouse for sediments eroded and transported from the Himalayan mountains. This fluvial landscape provides sufficient groundwater and fertile lands that support the agricultural activities to sustain the livelihood of a vast population. The Ganga plains exhibit a broad array of geomorphic features associated with the fluvial environment of deposition. The interfluve between the Ganga and Sai rivers in the Central Ganga Plains has been documented to be the oldest geomorphic surface in the region. Narrow meandering loops of streams, stretches of linear lakes representing sinuous abandoned channels and meander cut-offs, small ponds, and oxbow lakes can be observed in the elevated interfluve of both these rivers. The presence of numerous oxbow lakes and small isolated pools as remnants of the abandoned channels is a testimony to a highly active fluvial setting in the past.
In order to understand the evolution of the linear belt of meander cut-offs and oxbows in the Ganga-Sai interfluve, both regional and local scale geomorphic mapping was done using the earth observation satellite imageries and a multi-temporal approach was followed to efficiently trace all the observable geomorphic features in this fluvial setting. The regional scale geomorphic mapping of this interfluve shows a linear paleochannel belt comprised of meander cutoffs and small abandoned channel segments run parallel to the present-day Sai river. A large oxbow lake (Baraila Tal) was selected from this linear belt of cutoffs and excavated at three locations to investigate the chrono-stratigraphic succession of these lakes. Results from the geomorphic analysis suggest that the belt of paleochannel remnants was previously a part of the avulsed channel of Sai river. Three stages of landscape evolution and development of various geomorphic features related to channel migration between the Late Pleistocene and Holocene period in the Ganga-Sai interfluve region in the Central Ganga Plains have been identified. Stratigraphic succession at Baraila Tal shows the presence of micaceous sandy material at the base which suggests that the lake was previously a part of an active fluvial system. This litho-unit is overlain by the finer clayey silt and silty clay deposits which indicate that the depositional environment transformed from a fluvial to a lacustrine system. The proposed evolutionary pathway has been validated using results of stable isotopic data generated from the micro-gastropod shells picked from the lake sediments of Baraila Tal in the Ganga-Sai interfluve.

How to cite: Misra, P., Singh, M., Tandon, S. K., and Sinha, R.: Geomorphic and stratigraphic evolution of floodplain lakes in the Central Ganga Plains, India, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13142, https://doi.org/10.5194/egusphere-egu22-13142, 2022.

In many mountain environments worldwide, the number of rainstorms capable of triggering debris flows has significantly increased in the last century. An increase in debris flow frequencies in recent times is often postulated but poorly substantiated due to a lack of continuous records over relevant timescales of environmental forcing, especially in the Alpine environment. In this study, onshore processes and the sediment record of an Alpine lake are assessed to reconstruct debris flow activity. The continuous sedimentation regime in lake Plansee (Tyrol, Austria) provides a long-term archive of natural hazards in a setting of highly connective catchment morphology. In an on- and offshore investigation, we integrate LiDAR data, swath bathymetry and sediment core analyses. Two types of alluvial fan deltas are characterized, which differ in sediment delivery and their geomorphic landforms in the terrestrial and subaquatic realm. In a core transect from one fan delta towards the depocentre, we distinguish turbidites related to debris flows and earthquakes. 138 debris flow events were identified in the 4,000 year sedimentary record. The event chronology reveals four phases of different debris flow recurrence. Here a constant background sedimentation with low debris flow rates contrasts to i) debris flow frequency increases interpreted as post-seismic landscape response and ii) a drastic 7-fold increase in debris flow frequency between the periods ~1520 to 1920 CE and 1920 to 2018 CE. These recently enhanced rates may link to the nearly doubled frequency of heavy rainfall events from 1920 to 2010 CE in the Plansee area. We provide sedimentological evidence for a previous LiDAR-based observation of increased debris flow recurrence at Plansee in the 20^th century. These results indicate that variations in debris flow activity are mostly controlled by a few severe earthquakes and by climate forcing.

Kiefer, C., Oswald, P., Moernaut, J., Fabbri, S. C., Mayr, C., Strasser, M., and Krautblatter, M.: A 4000-year debris flow record based on amphibious investigations of fan delta activity in Plansee (Austria, Eastern Alps), Earth Surf. Dynam., 9, 1481-1503, 10.5194/esurf-9-1481-2021, 2021.

How to cite: Kiefer, C., Oswald, P., Moernaut, J., Fabbri, S. C., Mayr, C., Strasser, M., and Krautblatter, M.: Deciphering debris flow activity in the lake sediment record of Plansee (Austria, Eastern Alps), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8541, https://doi.org/10.5194/egusphere-egu22-8541, 2022.

Depositional models for clastic sedimentation in large lakes, notably in rift lakes, emphasize on downslope river and gravity-driven processes. Wind-driven waterbodies (WWB), a recently-defined category of lakes, display features created by wave related processes and wind-induced water circulation such as beach ridges or spits along the coasts, as well as sediment drifts, sedimentary shelf progradation and erosional surfaces in deeper, offshore domains. A coupled hydrodynamic, wave and sediment transport three-dimensional Delft3D model was established for Lake Turkana, East Africa, one of the world’s greatest lakes in order to test the WWB validity for fine sediments. Using available data, the model is forced for 1.5 years with river liquid and solid discharge, as well as wind data, in order to simulate cohesive sediment transport and resuspension. The model simulates stratification due to salinity, wave generation and dissipation, and sediment advection and resuspension by waves and currents, with multiple cohesive sediment fractions. Model results were compared with remote sensed imagery and with available in-situ sediment deposition rates, reproducing the general surface suspended sediment patterns, and agreeing with the mass deposition rates data from the literature.

By creating scenarios in which certain processes were switched off, the contribution of waves resuspension, wind-induced currents, salinity-induced stratification, and river jet, in resuspending and transporting sediment along the lake could be investigated. With just the wind and/or the river influence, most of the sediment deposition occurs in the first 10 km from the river mouth and at depths from 0 to 10 m. When waves are switched on, significant quantities of sediments can be resuspended by waves, and most of the sediments are deposited in the first 30 km from the river mouth, at depths from 10 to 30 m. This study provides insights on sediment transport in the Lake Turkana, and similarly in great lakes in general, supporting waves as the main agent transporting fine sediments away from river mouths into deeper areas, as opposed to river-plume derived transport.

How to cite: Zainescu, F., Schuster, M., van der Vegt, H., Storms, J., Nutz, A., Bozetti, G., May, J.-H., Bouchette, F., and May, S. M.: Predominance of wind-wave transport and resuspension of fine river sediments in a great lake: A Delft3D modelling study of lake Turkana, East African Rift, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11771, https://doi.org/10.5194/egusphere-egu22-11771, 2022.

Inner-Alpine lakes typically present a complex sedimentary record, with changing sediment dynamics and event deposits related to different natural hazards. Lake Altaussee (712 m asl; 2.4 x 1.0 km; max. 72 m deep) is a moderately sized lake located within the Northern Calcareous Alps. It is mainly fed by several subaqueous springs associated to a regional karst plateau (“Totes Gebirge”). This spring activity produced several craters (up to 60 m in diameter and 22 m deep) on the lake bottom. Within the framework of the Walter Munk Foundation for the Oceans (WMFO), a multidisciplinary research effort is undertaken to understand the lake system.

Here we present first results based on sedimentological and geochemical analysis (XRF core scanning) of four long sediment cores (3-9 m long) collected in summer 2021. The cores were taken in different depositional environments, such as the deep central basin, a shallow plateau in the western part and on the outer slopes of the largest karst crater. The sediment cores were dated by ¹⁴C  and are further interpreted based on observations on  subbottom profiling data and high-resolution multibeam bathymetry.

The deep basin core (9 m long; 52 m water depth) reveals a ~2.5 m thick megaturbidite (MT) characterized by an overall normal grading and a thin fine-grained cap layer. The MT is overlying a ~1.3 m thick mass-transport deposit consisting of a mixture of remobilized organic-rich lake-internal sediment and coarser cm-scale pebbles. Morphologic and seismostratigraphic mapping indicate that this megaturbidite was formed by massive sediment remobilization due to multiple (synchronous?) rockfalls and/or sudden remobilization of accumulated slope deposits impacting the eastern part of the lake basin around 724-931 CE.

This event deposit overlies several brighter-colored, rather homogenous units, which are separated by a 20 cm thick dark organic-rich laminated interval. Preliminary dating of these lower units to about 8-10 kyrs BP suggest the existence of a hiatus of several millennia between the MT and the lower units. To verify whether this is caused by erosion related to the mass-transport event or a period of non-deposition, we analyzed a long core (6 m long; 22 m water depth) on the western plateau. This core exhibits a Late Glacial clastic varve sequence (~14-15 kyr BP), overlain by  a unit of poorly-sorted debrite(s) and an organic-rich lacustrine sediment sequence deposited during the past ~1.2 kyr which can be traced in all short cores and seismic profiles throughout the lake. Altogether these observations suggest highstand conditions during Late Glacial times, a significantly lower lake level during large parts of the Holocene, and again highstand conditions during the past 1.2 kyrs.

The identification and stratigraphic position of numerous clastic outflow deposits on the outer slope of the largest karst crater hint at a sudden onset or intensification of spring activity in the Late Holocene at this location. Whether this can have contributed to the hypothesized lake level rise in this inner-alpine basin remains unclear and forms the focus of ongoing multidisciplinary investigations.

How to cite: Rechenmacher, J., Ortler, M., Moernaut, J., Häuselmann, P., Fiebig, M., and Heine, E.: The Holocene sediment record of Lake Altaussee (Salzkammergut, Austria): A perspective on mass movements, lake level change and varying karst spring activity in an inner-Alpine setting, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3952, https://doi.org/10.5194/egusphere-egu22-3952, 2022.

Lake Cadagno, a meromictic, redox stratified lake located in Val Piora in Switzerland has extensively been studied serving as a modern analogue of the Archean/Proterozoic ocean. Euxinic conditions were established after a short transition interval immediately following lake formation ~10’000 years ago. Overall elevated but very variable Mn concentration during this transition period have been thought to reflect fluctuating bottom water redox condition with authigenic accumulation of sedimentary Mn from the water column in line with observation from deep basins of the Baltic Sea.

To test this hypothesis we measured the Mo isotopic composition of Lake Cadagno sediments with a focus on the transition interval following lake formation between 7.4 and 7.8 m depth. With a δ^98/95Mo_NIST+0.25 composition ranging from -1.72 to +3.77‰ the Mo isotopic variability of the transition interval sediments is significantly larger compared to Cadagno sapropels deposited under euxinic conditions and significant larger compared to the entire Mo isotopic variability observed in marine reservoirs. Aside this large variability in δ^98/95Mo_NIST+0.25 a gradual change from isotopically very light to very heavy Mo isotopic composition upcore is observed. This transient sedimentary Mo isotope pattern cannot be explained by fluctuating bottom water redox conditions at the beginning of the lake and cannot be a primary signature caused by changes in the depositional environment. Likely, the inflow of oxic groundwater from subsurface karst aquifers present in Cadagno into organic-matter-rich lake sediments, a likely active and currently ongoing process, causes the formation of a chemocline at depth in the sediment column. Here the reduction of sulphate and the precipitation of isotopically light Mo from the dissolved oxic groundwater reservoir causes progressively higher δ^98/95Mo_NIST+0.25 upwards in the sediment column.  

How to cite: Wille, M., Vogel, H., Berg, J., and Pellaton, J.: Groundwater induced sediment diagenesis in LakeCadagno, Switzerland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11833, https://doi.org/10.5194/egusphere-egu22-11833, 2022.

Tropical Lake Sentani in the Indonesian Province Papua consists of four separate sub-basins and is surrounded by a geologically  diverse catchment. Also, strong morphological differences between the sub-basins result in a unique water column structure for each basin, ranging from fully mixed to meromictic. We characterized the surface sediment (upper 5 cm) of the lake’s four sub-basins based on multivariate statistical analyses (Principal Component Analysis, hierarchical clustering) of major element compositions obtained by X-ray Fluorescence (XRF) scanning. Three types of sediment are identified based on distinct compositional differences between rivers, shallow/proximal and deep/distal lake sediments. The different sediment types are mainly characterized by the amounts of organic carbon (TOC) and sulfur on one side and elements associated with siliciclastic rocks (Ti, Al, Si, K) on the other. Our study shows large spatial heterogeneity within the lake’s sub-basins that is mainly caused by catchment geology and topography, river runoff as well as the bathymetry and the depth of the oxycline.The samples from rivers and river mouths are dominated by siliciclastic elements and linked with coarser grain sizes as well as an abundance of mafic rock fractions or carbonates, depending on catchment geology. The sedimentary environment also controls the behavior of Fe and Mn, as these elements change from a positive correlation with siliciclastic elements in river samples to a negative correlation in the lake, indicating a more redox-sensitive behavior. These highly variable conditions make Lake Sentani a natural laboratory, with its different sub-basins representing different depositional environments under identical tropical climate conditions

How to cite: Kallmeyer, J., Nomosatryo, S., Tjallingii, R., Henny, C., Ridwansyah, I., Wagner, D., and Tomás, S.: Sediment composition and depositional environments in tropical Lake Sentani, Papua Province, Indonesia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1521, https://doi.org/10.5194/egusphere-egu22-1521, 2022.

Seismoacoustic studies are used to solve a wide range of different tasks, such as studying the bottom of water bodies and bottom sediments, detecting sunken objects, designing various structures (pipelines, port facilities, etc.), estimating the thickness of sapropel deposits, calculating their reserves, etc. In terms of paleoclimatic studies, the importance of such studies is increasing. The study of sediments of continental water bodies allows to get preliminary information about climate changes in the region with a very high resolution. Seismoacoustic profiling allows remote characterization of lake sediments stratigraphy due to the recordings of acoustic waves reflected from the lake bottom and underlying layers. Seismoacoustic studies were conducted to detect bottom sediments and choose the best place for core sampling in Lake Kandrykul (Republic of Bashkortostan, Russia). 

Continuous seismic profiling was applied based on the principle of central beam, which enables remote investigation of the lake bottom structure owing to the recording of acoustic waves reflected from the lake bottom. On this basis, it is possible to establish borders between sediment layers of different physical properties. The seismoacoustic profiling was carried out using specialized complex, designed and manufactured on the base of Kazan Federal University. The complex includes: a source of elastic waves, a receiver, a seismic station, a laptop, a GPS-receiver, an inflatable boat, an electric motor, and power supply elements. The complex enables us to get seismic acoustic sections with vertical resolution at least 15 cm; depth study of various types of lake sediments at least 15 m; geodetic positioning system within several meters. It also provides the digital recording of information. As a source of elastic waves an inductive oscillator "boomer" was used. A storage battery was used as a source of electric power. The GPS receiver was used to coordinate profiles and boat location.

There were obtained 6 high resolution seismic sections. The total length of the profiles was more than 16 km. According to seismic data the depth of the lake is 15 meters. The thickness of bottom sediments is more than 7 m, which indicates the great age of the lake. Thus, the lake is suitable for studying climate changes in the past for this region. On the seismic section, it is clearly seen the moment of the lake formation, when the lake layered sediments began to accumulate.

This study was funded by the Russian Foundation for Basic Research under the grant #20-05-00833. Part of the study was funded with the subsidy allocated to the KFU in context of state assignment # 671-2020-0049.

How to cite: Krylov, P., Nurgaliev, D., Kuzina, D., Dautov, A., and Yasonov, P.: High-resolution seismic studies of shallow lake Kandrykul (republic of Bashkortostan, Russia)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4686, https://doi.org/10.5194/egusphere-egu22-4686, 2022.

Recently, non-traditional stable isotope systems have become new tools to track weathering and sediment transport processes and to obtain information about the lithological and chemical composition of drainage networks. Because the Ti isotope composition (δ⁴⁹Ti) increases with the SiO₂ concentration of rocks, Ti isotopes have received increasing attention to reconstruct the chemical composition of the continental crust through time (Greber et al., 2017). Chemical weathering and hydrodynamic sorting of sediments during transport may however cause fractionation of Ti isotopes and bias the δ⁴⁹Ti of the sediment record (Klaver et al., 2021; Xinyue et al., 2022).

To investigate potential biases and their extent in the sedimentary record, we measured the δ⁴⁹Ti signature of lacustrine sediments and respective catchment bedrock and weathering profiles from two study areas that represent geochemical and weathering endmembers; (i) Lake Grimsel in Switzerland displaying a felsic catchment dominated by physical weathering and (ii) Lake Towuti in equatorial Sulawesi, Indonesia, with an ultramafic to mafic catchment and intense chemical weathering.

Shallow sediments collected at Lake Grimsel composed of different particle sizes ranging from clay to gravel, as well as samples from a sediment core spanning the past 10 kyr, display a constant δ^49/47Tiof +0.32 ± 0.03‰. This value is expected from the granodioritic protolith in the catchment. We also did not find any Ti isotope fractionation associated with chemical weathering based on two soil profiles from the catchment of Lake Towuti in Indonesia. Furthermore, samples from a sediment  core from Lake Towuti spanning the past ~1 Myr display δ⁴⁹Tiin a narrow rangebetween +0.09 to +0.17 ‰ (both ± 0.03‰; 2SD), and this value is between the Ti isotope signature present in soil and bedrock in the catchment that range from +0.07 to +0.26‰ (both ± 0.03‰; 2SD). Due to the heterogeneous δ⁴⁹Ti of the catchment of Lake Towuti further mass balance modeling is required to assess if the Ti isotopic composition of the lake sediments reflects that of the eroded protolith.  

REFERENCES

Greber, N. D., Dauphas, N., Bekker, A., Ptáček, M. P., Bindeman, I. N., & Hofmann, A. (2017). Titanium isotopic evidence for felsic crust and plate tectonics 3.5 billion years ago. Science, 357(6357), 1271-1274.

Klaver, M., MacLennan, S. A., Ibañez-Mejia, M., Tissot, F. L., Vroon, P. Z., & Millet, M.-A. (2021). Reliability of detrital marine sediments as proxy for continental crust composition: The effects of hydrodynamic sorting on Ti and Zr isotope systematics. Geochimica et Cosmochimica Acta.

Xinyue, H., Jinlong, M., Gangjian, W., Zhibing, W., Le, Z., Ti, Z., & Zhuoying, Z. (2022). Mass-dependent fractionation of titanium stable isotopes during intensive weathering of basalts. Earth and Planetary Science Letters, Volume 579.

How to cite: Vilela, N., Vogel, H., Russell, J. M., Bijaksana, S., and Greber, N. D.: Titanium isotopes in detrital sediments: A reliable proxy for the protoliths composition?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12980, https://doi.org/10.5194/egusphere-egu22-12980, 2022.

The pH is a fundamental determinant for physico-chemical reactions in aquatic environments but notoriously difficult to reconstruct in paleo records. Experimental studies have shown that the δ⁶⁶Zn isotopic composition of calcite is strongly pH dependent in the 7.0 ≤ pH ≤ 8.0 range, with lower δ⁶⁶Zn at higher pH, making it a suitable pH proxy in settings with endogenic calcite precipitation (Mavromatis et al. 2019). Here we applied the calcite δ⁶⁶Zn pH proxy to a sediment core covering the recent anthropogenic eutrophication at Lake Greifen, Switzerland to test its applicability in a natural setting that has undergone a productivity-driven shift in surface water pH. Lake Greifen is a hard water lake with a surface water pH ranging between >8.5 during spring and summer algal blooms and ~7.5 in the remainder of the year. Sediments deposited in the center of the lake are predominantly composed of endogenic calcite (>75 %wt) with the remainder comprising varying amounts of organic matter and biogenic silica and only minor detrital matter. Pure calcite samples for this study were collected from sediments deposited during both the oligotrophic and eutrophic lake phases to capture a wide range in pH. Lake Greifen sedimentary calcite δ⁶⁶Zn values relative to the JMC3-0749L standard range between 0.71 ± 0.05 ‰ in sediments deposited under oligotrophic conditions to 0.29 ± 0.01 ‰ in sediments deposited under eutrophic conditions. Lower δ⁶⁶Zn values during the more recent eutrophic lake phase may thus be explained by a productivity-driven change in surface water pH. Interestingly, δ⁶⁶Zn values around 0.3 ‰ have been reported for calcite precipitating at pH >8 in experimental studies, which is very close to Lake Greifen’s modern surface water pH recorded during spring and summer algal blooms. δ⁶⁶Zn values around 0.7 ‰, reported in samples originating from the less productive oligotrophic phase of Lake Greifen, are indicative for a pH <7 in experimental studies. Additional data from other settings with varying δ⁶⁶Zn water isotope compositions are required to further confirm our findings but the preliminary results of this study suggest δ⁶⁶Zn_calcite to be a promising pH proxy candidate in paleo records.

Reference

Mavromatis, V.; Gonzalez, A.G.; Dietzel, M.; Schott, J. (2019) Zinc isotope fractionation during the inorganic precipitation of calcite – Towards a new pH proxy. Geochimica et Cosmochimica Acta 244, 99 – 112.

How to cite: Vogel, H., Engler, A., and Bigalke, M.: Sedimentary calcite Zn isotope composition as a possible paleo pH proxy – a case study from eutrophic Lake Greifen, Switzerland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4734, https://doi.org/10.5194/egusphere-egu22-4734, 2022.

The Pliocene (5.33-2.68 Ma) was the last significant warm period in Earth's climate history. Atmospheric carbon dioxide and global temperatures during this interval are comparable to those estimated for our planet’s future climate trajectory. Considering a comparable to present continental and oceanic positioning, it is possible to assume similar oceanic and atmospheric circulation patterns, and hence reliable Pliocene climate archives may serve as a strong analogue for future climate conditions of the planet. Current data on the Pliocene mostly focus on marine sediments with terrestrial data stemming from loess and paleosol records. Yet, there is a lack of information from continental lacustrine formations, especially from the East Mediterranean. The ‘Erk-el-Ahmar Formation (3.15-4.5 Ma) lies in the central Jordan Valley and includes a ~150 m succession of fluvio-lacustrine deposits (clay, silt, very find sand, and carbonate layers), with excellent preservation of freshwater mollusk shells, ostracods, micromammal bone fragments, and mammoth remains. This study will reconstruct the paleoenvironmental conditions of the region during this time interval using a multiproxy approach that includes physical parameters (grain size distribution, magnetic susceptibility), geochemical compositional data (X-ray fluorescence and total organic carbon/inorganic carbon), with preliminary results of ostracod and biomarker data from two push-cores (40 m) and the formation’s outcrop.

Our results show major fluctuations in the lake hypsometry, as evidenced by the different parameters, which might reflect the local hydro-climate conditions. An orbital-scale dry-wet climate cyclicity is well identified in the sedimentary record, which influenced the lake depth, redox conditions, sedimentary provenance, and the habitat for faunal species. The cores capture transitions between continuous shallow and deep lacustrine environments, with potential short intermittent events (perhaps seismic or climate-induced), indicating the sustainability of this perennial water body. Results from this study provide an important understanding of the hydrological conditions that may have dominated the region during a warm climate phase, challenging previous estimations.

How to cite: Greenlee, J., Dean, S., Hall, C., Castañeda, I., and Waldmann, N.: Reconstructing Pliocene environmental changes in the East Mediterranean: results from a new multi-proxy study on a lake sedimentary record from the central Jordan Valley, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8468, https://doi.org/10.5194/egusphere-egu22-8468, 2022.

Lake Urmia, a hypersaline lake in NW Iran, is situated in a tectonically active and climatically sensitive region. It has been gradually desiccating, endangering its unique biodiversity, including an endemic brine shrimp, Artemia urmiana. The present study documents multiproxy analyses of a 25 m-long sediment core recovered from the northern part of Lake Urmia. Lake sediment multiproxy data provide the basis for extensive documentation of lake history, climatic changes, as well as sedimentation processes. The timing of variable climatic conditions in the lake is determined by the age-depth model of the core based on radiocarbon dating. Four well-dated radiocarbon ages obtained from pollen samples suggest a late Quaternary sequence. However, generating a reliable and continuous age-depth model requires additional age data. Visual lithological observations and physical properties of the sediments document high lithofacies variations throughout the core. The sedimentary sequence is composed of biochemical and terrigenous mud and sand, micrite and clay minerals, sulfate and chloride minerals, and fecal pellets of Artemia and coated grains. The core sediments were subdivided into six sedimentary units. The lowermost part consists of dark grey-coated grains. The overlying unit consists of silty clay that varies from brown to greenish-grey and alternates with fecal pellets and coated grains. The subsequent unit is composed of brown clay minerals and fecal pellets. The upper boundary of the next unit, consisting of alternations of sulfate minerals (mostly gypsum) and fecal pellets, is marked by a color change from brown to greenish-grey. The uppermost-examined sediments are richer in pellet content; towards the top, pellets are fewer and are in a carbonate matrix. A salt crust (up to 3 m) from a recent drying event constitutes the surface sediments. These findings are combined with high-resolution µ-XRF and TOC analyses to infer a complete picture of paleoenvironmental variations on the lake. Hypersaline lakes are extreme habitats, mostly with very low productivity. However, high TOC content in some parts of the core can be attributed to organic matter production. The high-resolution smear-slide observations indicate that high TOC content mainly corresponds to rich fecal pellet layers. Intense fluctuations in the elemental profiles imply high variations in paleoclimate. The Ca-Ti ratio correlates positively with TOC content, indicating endogenic carbonate production due to the warm and dry climate. The general low µ-XRF Fe-Mn ratio throughout the core strongly suggests that the deep-water column in the lake could never have been anoxic but mostly suboxic to oxic due to high water circulation as a consequence of low lake level. The warm and wet climate period can be documented in µ-XRF K, Fe, and Ti profiles, partly supported by high MS values. Lower Ca-Sr ratios in the µ-XRF mainly correspond to sulfate minerals, primarily gypsum. We also carried out high-resolution pollen studies that brought further insights into the reconstruction of paleovegetation and paleoclimate changes. This work is supported by the TUBITAK 118C329 and ITU BAP 42972 projects.

How to cite: Ertunç, G., Eriş, K. K., Mohammadi, A., Çiner, A., Lak, R., Biltekin, D., and Yetemen, Ö.: Late Quaternary paleoclimate and paleoenvironment changes in Lake Urmia, NW Iran, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7696, https://doi.org/10.5194/egusphere-egu22-7696, 2022.

Lake Paravani is located in the Republic of Georgia at an altitude of 2073 m on the volcanic Javakheti Plateau (Lesser Caucasus). Although first studies were conducted at the lake the last years, many questions remain unsolved regarding to the sedimentation pattern and the landscape evolution in general. Hence, we aim to deepen the understanding of landscape genesis during the Holocene and beyond. Therefore, a coring transect of eight cores was taken in the southern part of the lake and two of these sediment cores, ICE001 and ICE006, were analysed with respect to (i) landscape, vegetation and climate evolution since the Pleistocene, and (ii) their processes. By using an applied multi-proxy approach, sediment properties in terms of granulometry, geochemical composition, magnetic susceptibility, organic content, and palynology were analysed.

The results suggest high lake levels for the period from about 28 to 16 ka BP, inferring a cold and humid climate in the Lake Paravani basin. The landscape was covered by glaciers, which act as drivers for the prevailing physical weathering while sparse vegetation and poorly developed soils dominated around Lake Paravani. Since 16 ka BP, a declining lake level is identified, from which a significant increase in aridity is inferred while temperatures remain constantly low. The accompanying shift of facies into the sublittoral establishes variable depositional conditions at the site of borehole ICE001. For this reason, the transition from glacial to interglacial is poorly recorded. Early and middle Holocene deposits were eventually eroded during lake level fluctuations. A palaeobeach facies at approximately 4.5 ka BP displays low lake level and indicates high aridity. The period from 4.5 ka BP to present was characterized by rising lake level to recent conditions. Furthermore, increasing productivity within the lake, as shown by the total organic content, indicates warmer temperatures, and consequently increasing intensity of chemical weathering. In addition, vegetation cover established and soils developed. 

How to cite: Gademann, D., Ustiashvili, N., Navrotishvili, L., Tiiu, K., Elashvili, M., Brückner, H., and Laermanns, H.: Late Pleistocene and Holocene landscape evolution at Lake Paravani (Lesser Caucasus, Georgia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11512, https://doi.org/10.5194/egusphere-egu22-11512, 2022.

In this study, we studied palynomorphs from the alpine record from Laguna Seca in Sierra Nevada, southern Spain to investigate the response of forests and lake environments in the western Mediterranean area to climate changes and to human impact during the latest Pleistocene and Holocene. Xerophyte herbs such as Artemisia, Ephedra, and Amaranthaceae are highest during the late Bölling-Allerod (BA) and Younger Dryas (YD) indicating aridity. Poaceae (grasses) are maximum in the BA and Early Holocene, probably indicating expansion in the barren areas left by glaciers after deglaciation. Forest abundance and composition, in particular of deciduous Quercus and Pinus species indicates maximum humidity during the Early Holocene and aridification in the Middle and Late Holocene. Microcharcoal analysis done on the palynological preparations agrees with the vegetation changes, showing maxima in the Early and Middle Holocene and a decrease in the Late Holocene when the Mediterranean vegetation, and thus fuel availability, diminished. The record of Laguna Seca is particularly interesting with respect to the algae and other aquatic microscopic remains. Pediastrum algae only occurred and showed very high abundances during the end of Heinrich Stadial 1 and beginning of the BA, probably indicating deepest lake conditions with deglaciation. Botryococcus, Debarya, Spirogyra and Zygnema algae also peaked at that climate transition, also supporting lake conditions. Botryococcus increased during the Early Holocene, while the rest of the algae almost vanished, which could indicate that the lake became shallower but very productive until 8200 cal yr BP. From then on, the lake level lowered and became a seasonal lake in the Middle-Late Holocene transition.

How to cite: Jiménez-Moreno, G., López-Avilés, A., García-Alix, A., Ramos-Román, M. J., Camuera, J., Mesa-Fernández, J. M., Jiménez-Espejo, F. J., López-Blanco, C., Carrión, J. S., and Anderson, R. S.: Environmental and climate change in Sierra Nevada (S Spain) during the latest Pleistocene and Holocene, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7505, https://doi.org/10.5194/egusphere-egu22-7505, 2022.

The alpine wetlands from Sierra Nevada mountain range, located in the western Mediterranean region, are highly sensitive to climate and environmental changes and their sedimentary records preserve a high-quality signal of past natural environmental conditions. Previous studies from the Sierra Nevada show that alpine wetland formation occurred principally during the YD-Early Holocene transition in former glacier cirque areas and thus older sedimentary records are lacking from that area. In this study, we present the Laguna Seca (LS) record, which is the longest and oldest sedimentary record (14.1 meters and 18 cal kyr BP, respectively) ever retrieved in the alpine Sierra Nevada. In this record we have carried out detailed chronological and sedimentological analyses and we have obtained magnetic susceptibility, total organic carbon, and carbon/nitrogen data with the main goal of understanding how alpine environments of this region responded to climate variations since the last glacial-interglacial transition. Four climatically-controlled facies associations have been identified and interpreted in terms of transport mechanisms and paleoenvironments: (1) subaerial cohesionless debris flows during a paraglacial stage, (2) till or nival diamicton during a small glacier/nivation hollow stage, (3) massive mudstone by suspension settling of clays into standing water during a lacustrine stage from ~15.7 cal kyr BP to the present and; (4) frost-shattering breccia deposited inside the lacustrine stage, only in an area of the wetland, probably during the YD and related with a periglacial substage. The increase in summer insolation, temperatures and precipitation in the western Mediterranean area probably boosted a significant ice-melting and the glacier retreat in the Sierra Nevada, triggering the development of a deep lake in LS ~15.7 cal kyr BP with an important organic matter contribution until the end of the Early Holocene (except in the Younger Dryas that probably the lake level dropped). The general long-term aridification trend observed in the western Mediterranean region from the Middle Holocene to the present triggered the evolution from deep to ephemeral lacustrine conditions with an increase in aquatic productivity in the LS basin that ended up with the current summer desiccation of the lake.

How to cite: López-Avilés, A., Jiménez-Moreno, G., García-Alix, A., García-García, F., Camuera, J., Anderson, R. S., Sanjurjo-Sánchez, J., Arce Chamorro, C., and Carrión, J. S.: Sedimentary and environmental evolution of an alpine lake in Sierra Nevada, western Mediterranean region, since the last deglaciation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7824, https://doi.org/10.5194/egusphere-egu22-7824, 2022.

The Serra da Estrela range in Central Portugal is a key  region to explore the Last Glacial termination in the Atlantic region of Iberia. We present the Late Glacial and Holocene record of Lake Peixão to reconstruct past environmental and climatic conditions at decadal timescales. We retrieved an 8.5m long core in the central and deepest zone of the lake. From the base to the top, the sediment core is composed of i) a thick layer (aprox. 0.5 m) of gravel-to-sand quartz clasts; ii) an alternation of one meter thick grey to pale-brown sandy deposits; and iii) homogeneous dark brown and pale-brown organic-rich muddy facies (ca. 7 meters). Using a Bayesian statistical model based on 16 radiocarbon dates using pollen concentrated samples and ²¹⁰Pb measurements, we have developed an age-depth model covering the last ca. 14.6 ka, recording the onset of the lake at that time. Lake and mire records previously published in the area generally support this chronology for the formation of proglacial lakes. In addition, the proposed timing for the disappearance of the Serra da Estrela glaciers has been based on Cosmic-Ray Exposure dating (in situ cosmogenic ³⁶Cl) of exposed moraine boulders and glacially polished bedrock surfaces. These results indicate that the end of the glacier’s presence in Serra da Estrela occurred at ca. 14.2 ka BP (during the Bølling-Allerød Interstadial). Therefore our results broadly suport the timing of the end of the deglaciation at the Serra da Estrela and highlight the value of lake sedimentary records. Moreover, the availability of last termination and Holocene highly-resolved sediments from Lake Peixão is likely to record very valuable evidence of climatic and environmental changes at decadal timescales extending from the last deglaciation, through the Holocene. This new multi-proxy data of the Lake Peixão sedimentary sequence will enable comparisons to other decadal-resolved records and support further investigations from the Mediterranean Iberian region.
The financial support for this work was possible through the following FCT project: HOLMODRIVE—North Atlantic Atmospheric Patterns Influence on Western Iberia Climate: From the Late Glacial to the Present (PTDC/CTA-GEO/29029/2017).

How to cite: Hernández, A., Santos, R. N., Rodrigues, T., Oliveira, D., Naughton, F., Moreno, J., Raposeiro, P., Giralt, S., Sáez, A., Leira, M., Gil-Romera, G., Costa, P., Trigo, R. M., Vieira, G., Abbott, M., Griffore, M., Gomes, S., and Ramos, A. M.: Deglaciation timing in the Atlantic Iberian mountains: an example from lake sediments in Serra da Estrela (Portugal), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4521, https://doi.org/10.5194/egusphere-egu22-4521, 2022.

The work is devoted to the study of the magnetic parameters of Kandrykul lake sediments. The main aim of this investigation is to identify the events and trends of environmental and climate factors changes in the Late Quaternary.

The objects of research is located in Bashkortostan republic (54°30′10″ N 54°03′50″ E).

According to previously seismoacoustic studies, 4 core columns were taken. The total number of samples for Lake Kandrykul was 659 (the length of column varies from 378 to 524 cm).

For a detailed complex analysis, core No. 3 was selected according of the primary lithological description and the results of seismoacoustic studies.

The detailed complex analysis included the measurements of magnetic susceptibility and natural remanent magnetization, coercive spectrometry, differential thermomagnetic analysis.

Magnetic susceptibility was measured using a Multifunction Kappabridge MFK1-FA (AGICO). Natural remanent magnetization was carried out at the Resource Center "GEOMODEL", Scientific Park of Saint-Petersburg State University. Hysteresis parameters were obtained using the J_meter coercitive spectrometer, and it allows to make separate measurements of the remanent and induced magnetizations in magnetic fields up to 1.5 T at room temperature, induced magnetization versus temperature. Differential thermomagnetic analysis was carried out for tracing magnetic minerals according their Curie temperature. Measurements were carried out on Curie express balance. The temperature dependence of induced magnetization in air at a heating rate of 100 °C/min up to a maximum temperature of 800°C were measured in a constant magnetic field - 400 mT.

Normal magnetization curves were used to determine the hysteresis parameters, the domain structure and ferrimagnetic grain sizes, as well as the contribution of para-, ferro- and superparamagnetic components to the total magnetic susceptibility.

Magnetic susceptibility varies between (0.54 – 21.94)*10^-7 м³/kg for all cores. The values of natural remanent magnetization changes from (0.099-302.41)*10^-3 A/m. Almost all magnetic fractions are presented by pseudo-single domain particles, according hysteresis parameters. According to differential thermomagnetic analysis magnetic minerals in sediments presented by iron sulfides and magnetite.

The results of magnetic-mineralogical investigations made it possible to reveal the features of climatic and other environmental changes on the studied lacustrine sediments.

This study was funded by the Russian Foundation for Basic Research under the grant #20-05-00833. Part of the study was funded with the subsidy allocated to the KFU in context of state assignment # 671-2020-0049.

How to cite: Kuzina, D., Yusupova, A., Nurgaliev, D., Krylov, P., and Antonenko, V.: Lacustrine sediments variability on the base of magnetic properties of lake Kandrykul, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11032, https://doi.org/10.5194/egusphere-egu22-11032, 2022.

Alpine lakes and peat bog from Sierra Nevada mountains in southern of Iberia are excellent paleoarchives since ecosystems are especially sensitive to climate variability and have been unaltered by humans until very recently. The Borreguil de la Virgen is a north-faced peat bog (BdlV; 37° 03′ 15″N, 3° 22′ 40″ W) located at 2945 m above sea level in a depression formed during the glacial retreat. A sedimentary record of 169 cm length has been analyzed by inductively coupled plasma-optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) to obtain major and trace elemental composition, respectively. Different geochemical proxies have been used to reconstruct the paleoenvironmental evolution in the BdlV during the Holocene. Rb/Al, Zr/Al and Ca/Al have been used as detrital proxies while Mo/Al and U/Al have been used has oxygenation proxies. The Rb/Al ratio showed the highest values between 8.5 and 5.5 cal ka BP suggesting enhanced runoff related to enhanced humid conditions. This period is also characterized by the highest sedimentation rates and high values of U/Al ratio. Pervasive high runoff input during this interval was interrupted by two periods of reduced values of Rb/Al ratio between 8 and 7.5 cal ka BP and around 7.2 cal ka BP. More arid and/or colder conditions could have reduced the precipitation, explaining the decrease in runoff. After 5.5 cal ka BP the Rb/Al depicted a decreasing trend, suggesting less humid conditions and an aridification trend. At 5.5 cal ka BP the Zr/Al ratio also increased, which suggests the onset of the Saharan eolian dust export as result of the African Humid Period demise. Between 5.3 and 3.6 cal ka BP a major environmental change occurred involving the drying of the wetland, which promoted increases in the Mo/Al ratio due to the less oxic conditions and in the Ca/Al ratio since the Ca dissolved in water precipitated. This environmental change is followed by a period of low sedimentation rate between 3.6 and 1 cal ka BP which precludes us to make any accurate interpretation. The comparison between elemental ratios from BdlV with other nearby lake and bog records from Sierra Nevada highlight that the peat bogs are more prone to have enrichments in some elements when sedimentary conditions change, thus showing a higher local influence.

How to cite: Mesa-Fernández, J. M., García-Alix, A., Martínez-Ruiz, F., Rodrigo-Gámiz, M., Jiménez-Moreno, G., Jiménez-Espejo, F. J., López-Avilés, A., and Anderson, R. S.: Paleoenvironmental and paleoclimate evolution in an alpine peat bog in southern Iberia: a geochemical approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7648, https://doi.org/10.5194/egusphere-egu22-7648, 2022.

The Mediterranean region is a vulnerable area affected, among other environmental threats, by aridification and desertification processes that can cause soil salinization in areas rich in evaporite deposits. This is especially evident in the evaporite lake systems of southern Iberia, where a combination of both natural and anthropogenic causes gives rise to aridification and land degradation. In this study, we performed a multiproxy analysis (magnetic susceptibility, lithology, bulk organic geochemistry, inorganic geochemistry, and mineralogy) in the sedimentary record of the Laguna de la Ballestera playa-lake in southwestern Iberia in order to reconstruct the environmental evolution of this evaporitic area and potential human impacts during the Holocene. The most humid period registered in the Laguna de la Ballestera record was the Early Holocene with significant catchment runoff and high lake water levels. The lake size, lake level and catchment runoff decreased throughout the Middle and Late Holocene. This aridification trend is especially evident in the Late Holocene when gypsum precipitation enhanced. The highest gypsum contents were registered in the last millennium, especially after 1600 cal yr CE, probably related to important changes in the hydrology of the area, shifting from a (semi) permanent to a temporal and seasonal hydrological regime. These trends represent the local environmental responses to the western Mediterranean climate during the Holocene. The studied proxies did not evidence any potential human impact until the last century, when the catchment runoff and the playa-lake hydroperiod changed, probably related to changes in the land use.

How to cite: Garcia Alix, A., Jiménez Moreno, G., Gázquez, F., Monedero-Contreras, R., López-Avilés, A., Jiménez-Espejo, F. J., Rodríguez-Rodríguez, M., Camuera, J., Ramos-Román, M. J., and Anderson, R. S.: Holocene paleoenvironmental evolution of a playa-lake system in southwestern Iberia (western Mediterranean region), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7560, https://doi.org/10.5194/egusphere-egu22-7560, 2022.

The southern Iberian Peninsula has been especially sensitive to Holocene climate changes [1]. Climatic and environmental variability has been reconstructed by the mineralogical and chemical analyses of lacustrine sediments. In this study we show the preliminary chronological, lithological, geochemical and magnetic susceptibility results of the sedimentary record of the Laguna Grande de Archidona (southern Spain). This record covers the last 3300 years and it reveals three paleoenvironmental stages. (1) A phase of relative aridity occurred between 3300-3000 cal yr BP, evidenced by fluctuating values of magnetic susceptibility and the presence of gypsum levels, which suggest high evaporation and fluctuating detritic inputs to the lake. (2) A humid phase is identified from 3000 to 1500 cal yr BP, deduced by significant detritic inputs to the lake (high magnetic susceptibility values) due to high catchment runoff during this period. This was the most humid period in the record, agreeing with other regional paleoclimatic records of the Iberian Roman Humid Period (2800-1500 cal yr BP [2]). Additionally, smaller-scale climatic oscillations are shown by the Sr/Al ratio fluctuations and the alternance of some carbonate and gypsum levels during this period. (3) Finally, all the proxies show abrupt changes and higher variability during the last 1500 years, depicting an aridification trend. This paleoenvironmental and paleoclimatic reconstruction agrees with previous studies from the southern Iberian Peninsula that show an arid phase between 3300-3000 cal yr BP, most-likely related with pervasive positive NAO conditions [3], and a decrease in arboreal pollen in Sierra Nevada sites (e.g.,  Borreguil de la Caldera [4]). A humid phase is identified during the Iberian Roman Humid Period, coeval with a dominant NAO negative mode [3] and also identified by enhanced erosion rates in other southern Iberia areas, such as in Zoñar lake [2] and by the increase of arboreal pollen in several records [1]. Finally, a trend towards more arid conditions is registered after 1500 cal yr BP in southern Iberia records, such as in Zoñar lake, which shows runoff decrease [2], or in other sites of southern Iberia that exhibit an increase in grasses [1, 5].

[1] Ramos-Román et al. (2018), Climate of the Past 14, 117-137; [2] Martín Puertas et al. (2010), Climate of the Past 6, 807-816; [3] Olsen et al. (2010) Nature Geoscience 5, 808-812; [4] Ramos-Román et al. (2016), Quaternary Science Review 143, 84-95; [5] Jiménez-Moreno and Anderson. (2012), Quaternary Research 77, 44-53.

How to cite: Castillo Baquera, A., Garcia Alix, A., Gazquez, F., Jimenez Moreno, G., Rodriguez Rodriguez, M., and Jimenez Espejo, F.: Late Holocene climatic variability in Southern Spain deduced from the sedimentary record of Laguna Grande de Archidona, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7602, https://doi.org/10.5194/egusphere-egu22-7602, 2022.

Algal communities in northern lakes respond sensitively to climate changes but their responses vary considerably between ecosystems. Functional approaches may help us better understand the nature of the biotic responses to environmental change, though presently this approach has rarely been used in northern lake environments. We explored patterns in diatom (Bacillariophyceae) species and functional composition during the Neoglacial in two shallow oligotrophic lakes typical of the Fennoscandian subarctic region. Sediment carbon and nitrogen isotope (δ¹³C, δ¹⁵N) and elemental biogeochemistry and spectral (visible-near infrared [VNIR] inferred lake-water total organic carbon [TOC] and sediment chlorophyll a) indices were used to track broad-scale environmental transitions over the past three millennia. A number of congruent change patterns were observed indicative of centennial to millennial scale changes in lake productivity, the inflow of organic carbon from land, and sediment organic carbon content. Both the dark colored woodland lake and the clear tundra lake displayed a gradual decline in lake water TOC concentrations attributed to Neoglacial cooling and transient increases in primary production associated with warmer periods and, in particular, the 20^th century warming. Although the Neoglacial evolution of the lakes showed similarities, diatom functional responses were not uniform between the lakes. In the dark woodland lake, functional shifts appeared most strongly connected to declining lake-water TOC and sediment organic carbon content, and were reflected, most notably, as a decline in motile species affiliated with high organic levels and low-light conditions. In the clear tundra lake, changes in lake productivity and sediment organic carbon were reflected most distinctly in the abundance of attached and colonial life forms but the relationships were more ambiguous. While many of the observed shifts aligned with expectations based on earlier research linking diatom functional traits to changing light and organic carbon levels, discrepancies among the lakes and functional groups call for further refinement to detect ecologically meaningful traits in divergent aquatic environments. Both species and functional composition in the two lakes indicated that, despite distinct anthropogenic imprints in the biogeochemical record, human impact on the lakes’ diatoms has not, as yet, been profound.

How to cite: Rantala, M., Kivilä, H., Meyer-Jacob, C., Luoto, T., Atti, S., Smol, J., and Nevalainen, L.: Functional diatom responses to Neoglacial environmental change in a dark and a clear shallow subarctic lake, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6340, https://doi.org/10.5194/egusphere-egu22-6340, 2022.

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial lipids that are used as paleotemperature and paleo-pH proxies. Developed originally for application in paleosoils, and geo-archives dominated by soil organic matter, they are also used for temperature reconstructions in lake sediments. For this, brGDGT ratios such as the MBT'_5ME are translated into mean annual air temperatures using linear transfer functions. However, water depth (Yao et al., 2019; Stefanescu et al., 2021) has recently been shown to influence the MBT'_5ME values in freshwater lakes. In addition, variable inputs of soil-derived GDGTs can skew the MBT'_5ME ratio values encountered in lake sediments. Unfortunately, the diagnostic ratios used to recognize either changes in water depth (HP5) or soil input (ΣIII/ΣII), are based on the relative abundance of the same 2 compounds (IIa and IIIa).

Currently, most of the work on environmental drivers of brGDGT lipids has been done on modern lake sediments. A view on the paleo-variability, i.e. the variability on brGDGTs in lacustrine archives, was still lacking. In this contribution, we will revisit several published and unpublished brGDGT records in last glacial and/or Holocene lake sediments that report a change in soil input and/or water level with time (e.g. Cao et al., 2021; Robles et al., 2022, Ramos-Román et al., submitted). We will use a compilation of these records to highlight how changes in hydrology and soil input influence brGDGT compositions. To distinguish between soil and lake-derived GDGTs, we will employ a novel machine learning approach (linear discriminant analysis). This method allows to identify soil and lake brGDGT distributions in modern soils and sediments (85% accuracy), and is now tested for the first time in paleolacustrine settings.

We show that natural or anthropogenic changes in the landscape can impact the diagnostic GDGT ratios for soil input and the MBT'_5ME ratio. The machine learning approach also allows to identify those depths where soil input is significant. This exercise is a first step in investigating the paleo-variability of brGDGTs with a machine learning approach, to determine variables that impact their downcore variability.

Cao J., et al. 2021. Lake-level records support a mid-Holocene maximum precipitation in northern China. Science China Earth Sciences 64, 2161–2171.

Ramos-Román, M. J., et al. Lipid biomarker (brGDGT)- and pollen-based reconstruction of temperature change during the Middle to Late Holocene transition in the Carpathians. Submitted to Global and Planetary Change.

Robles, M., et al. 2022. Impact of climate changes on vegetation and human societies during the Holocene in the South Caucasus (Vanevan, Armenia): A multiproxy approach including pollen, NPPs and brGDGTs. Quaternary Science Reviews 277, 107297.

Stefanescu, I.C., et al. 2021. Temperature and water depth effects on brGDGT distributions in sub-alpine lakes of mid-latitude North America. Organic Geochemistry 152, 104174.

Yao, Y., et al. 2020. Correlation between the ratio of 5-methyl hexamethylated to pentamethylated branched GDGTs (HP5) and water depth reflects redox variations in stratified lakes. Organic Geochemistry 147.

How to cite: De Jonge, C., Ramos-Román, M., Rowan, S., and Landry, Z.: What impacts long-term changes in biomarker-derived temperature in Holocene lake sediments: lake hydrology or watershed changes?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5447, https://doi.org/10.5194/egusphere-egu22-5447, 2022.

In this work, the methods and results of sedimentary and palaeoclimatological analyses of the modern lake sediment of Lake Bannoe are presented. The methods include coercive spectrometry, differential thermomagnetic analysis, particle-size analysis, δ C_org. The results are used to characterize the sediments and to study the changing climatological and environmental settings during the Holocene.

Lake Bannoe (53°35'48.13"N 58°37'47.28"E) is in the Southern Urals. The lake’s age model was constructed based on the radiocarbon dating of 9 samples. According to the model, the lake is ~12.5 thousand years of age. For a detailed complex analysis, core No. 3 was selected according of the primary lithological description and the results of seismoacoustic studies.

Hysteresis parameters were obtained using the J_meter coercitive spectrometer, and it allows separate measurements of the remanent and induced magnetizations in magnetic fields up to 1.5 T at room temperature, induced magnetization versus temperature. For 254 samples taken every 2 cm from core column #3, normal-magnetization coercive spectra were obtained.

Differential thermomagnetic analysis was carried out for tracing magnetic minerals according their Curie temperature.Measurements were carried out on Curie express balance. The temperature dependence of induced magnetization in air at a heating rate of 100 °C/min up to a maximum temperature of 800°C were measured in a constant magnetic field - 400 mT.

Particle size analysis was carried out on 15 samples using Microtrac Bluewave Particle Size Analyzer(Microtrac, USA). Previously, about 2 g of each sediment sample was used for the analysis. The organic matter and carbonate contents were removed by treating the samples with 30% H₂O₂ and 10% acetic acid. The three fractions (sand, silt and clay) are presented in sediments . Organic geochemistry (δ¹³C_org) was determined for 51 samples using Delta V Plus isotope mass spectrometer (ThermoFisher Scientific, Germany) with Flash HT prefix.

Normal-magnetization curves were used to determine the hysteresis parameters, the domain structure and ferrimagnetic grain sizes, as well as the contribution of k_para, k_ferro and k_super components to the total magnetic susceptibility. Variations in the paramagnetic content reflect the inflow of allothigenic clastic material into the sedimentation basin. The k_ferro component is represented by single-domain grains (presumably of biogenic origin) and multi-domain clastic grains. According to differential thermomagnetic analysis magnetic minerals in sediments mostly presented by iron sulfides and magnetite. The result of particle size analysis is showing, that the content of clay fraction in the sediment varies in the range (0.11-2.74) %, silt fraction from 71.51% to 94.5, sand - (2.76-26.71) %.The values of δC_org vary from -27.65 ‰ to -24.22 ‰. The periods of high and low humidity in the Southern Urals identified during the study are consistent with the Blytt–Sernander classification.

The present study of magnetic properties, grain size and organic geochemistry of core sediments from Lake Bannoe provides paleoclimatological record for South Ural for the Holocene Period.

This study was funded by the Russian Foundation for Basic Research, project #20-35-90058. Part of the study was funded by grant of the President of the Russian Federation for state support of young Russian scientists - candidates of sciences № MK-4100.2021.1.5.

How to cite: Anastasia, Y., Dilyara, K., Nouria, N., Pavel, K., and Vadim, A.: Holocene paleoclimate history of Lake Bannoe (South Ural), from magnetic, geochemical investigation, and grain‐size characteristics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6885, https://doi.org/10.5194/egusphere-egu22-6885, 2022.

Solar radiation fuels primary production and carbon uptake in aquatic environments, but shorter ultraviolet radiation (UVR) wavelengths may cause adverse effects and trigger photoprotective mechanisms in organisms inhabiting lakes. In sensitive mountain lakes, ice cover and dissolved organic matter (DOM) mainly control underwater light conditions. Climate warming and other anthropogenic pressures impact the length of the ice cover period and the concentration and composition of DOM. A prolonged growing season with increased light availability may change habitat availability and drive changes in the functional group distribution of phototrophic communities. However, the roles of changing habitats and possible adverse effects of UVR as drivers of micro-algae functional group distributions have not been separated, and lake studies have thus far mainly focused on species specific sensitivities.

This study focuses on changes in underwater light conditions and UVR exposure during the past ~200 years and the impacts on functional group distributions of diatom (Bacillariophyceae) communities in two mountain lakes with different altitude and catchment size. Dated short sediment cores from each lake were analysed for elemental composition and stable isotopes of carbon and nitrogen, as well as sediment-inferred lake water total organic carbon (TOC) and chlorophyll-a. Diatoms were analysed to the species level and further divided into eco-morphological groups to investigate parallel changes in diatom functional group distributions. Geochemical proxies were used to describe trends in lake water transparency and duration of ice cover period. In addition, changes in diatom functional group distributions were analysed from the main habitat in the shallow littoral zone to detect diatom functional groups tolerances to high UVR.

Anthropogenic pressure was identified as a likely driver of sediment-inferred lakewater TOC concentration changes within the past ~200 years, suggesting changes in light conditions and UVR. Diatom functional group distributions in the lake located at higher altitude with a smaller catchment showed an increase of planktic life-forms within the past ~100 year, which may be related to shortening of the ice cover period. Earlier studies have shown trade-offs between motility and photoprotective capacity, but in this study clear differences between occurrences of motile or non-motile functional groups in the shallow littoral zone were not found. Based on these results, further research with broader habitat sampling is needed to separate the roles of habitat availability and UVR, and their roles affecting the distribution of diatom functional groups.

How to cite: Atti, S., Rantala, M., Lami, A., Meyer-Jacob, C., Weckström, J., Smol, J., and Nevalainen, L.: Impacts of anthropogenic pressures on mountain lake underwater light conditions and diatom functional groups, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2896, https://doi.org/10.5194/egusphere-egu22-2896, 2022.

Diatoms (unicellular algae forming siliceous tests) are a significant component of the linked carbon-silicon (Si) cycles in that they consume Si released from the weathering of silicate rocks and subsequently sequester carbon and silica when buried in sediments. Thus, regions of diatom-rich sediment yield a window into the conditions that favor high carbon export rates and burial. We studied the Si sources (tributaries, hydrothermal vents) and sinks (diatomaceous sediment) of Yellowstone Lake, which is situated on silicate rich volcanic rocks, to elucidate Si cycling dynamics in the present and during the Holocene. 

Recent lake water, tributaries, and hydrothermal vent fluids from Yellowstone Lake were analyzed for their dissolved Si (DSi) concentration and stable silicon isotopes (δ³⁰Si) to aid in evaluating the sources of variability in the lake’s Si cycle. In addition, elemental composition (XRF), biogenic silica (BSi) content, and the diatom δ³⁰Si were analyzed in two sedimentary core records spanning the Holocene from a hydrothermally influenced area and an undisturbed deep portion of the lake to identify whether past hydrothermal explosions and disturbance by Mazama ash deposition affected Si cycling.

Combinations of the Si and δ³⁰Si mass balance, sedimentary BSi, diatom δ³⁰Si with XRF, and lithology data revealed that Yellowstone Lake has a resilient biogeochemical system influenced by consistently high hydrothermal input throughout the Holocene. Several of the hydrothermal explosions identified in the lithology had no identifiable long-term impact on BSi accumulation or the diatom δ³⁰Si signature. Both cores show similarities that suggest a stable and homogeneous DSi source across the entire lake. Thus, the diatom δ³⁰Si values record changes in the relative proportion of DSi sources, diatom production connected with changes in climate, and hydrothermal inputs.

How to cite: Zahajská, P., Fritz, S., Opfergelt, S., Stadmark, J., Cartier, R., and Conley, D.: Impact of hydrothermal activity on the Si cycle in Yellowstone Lake, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3571, https://doi.org/10.5194/egusphere-egu22-3571, 2022.