Displays

Water levels in Lakes Metzabok and Tzibaná, two large karst lakes in the Lacandon Forest of southern Mexico, declined dramatically within a two-week period in July 2019. Lake Metzabok (0.83 km²; z_max = 25 m) dried completely, whereas in Lake Tzibaná (1.24 km²; z_max = 70 m) it fell by ~30 m. Analysis of satellite images in Lake Metzabok suggested a combined reduction in surface area of ~0.86 km² and water volume loss of ~11.7 million m³. The sudden loss of such a large volume of water had negative impacts on local Lacandon Maya inhabitants, and profound ecological and environmental effects, in that it caused biodiversity loss.

We combined limnological and paleolimnological analyses to evaluate the ecological effects of the sudden loss of water from Lakes Metzabok and Tzibaná. We collected and analyzed remnant waters, surface sediments and short sediment cores from what remained of the water bodies to evaluate whether evidence for such drainage events is preserved in lake sediments. In situ water-column measurements yielded values similar to those from the previous six years when the lakes were filled, suggesting that evaporation was not the process responsible for lake level lowering, but rather that the lakes drained through fractures in the underlying karst bedrock. We collected phytoplankton and zooplankton samples from the remnant waters and found abundant diatoms, green algae, testate amoebae, crustaceans (copepods, cladocerans, ostracodes), insects (chironomids, trichopterans), collembolans, rotifers, tardigrades and nematodes. Environmental conditions in such small remnant ponds are probably stressful and unstable, but because many fish, the main predators in these ecosystems, did not survive the desiccation event, the aquatic environment is ideal for survival or recolonization by many invertebrate groups. Understanding the dynamics of this modern scenario with low lake levels is key for making paleolimnological inferences that use these aquatic bioindicators. We also investigated the commencing transition from an aquatic to a terrestrial habitat in Lake Metzabok. Abundant spiders colonized cracks in the dry sediment. Small, deep holes in surface mud were probably created by aquatic organisms when water levels decreased rapidly. Some cracks held rain water and were inhabited by tadpoles of the Gulf Coast toad (Incilius valliceps). The first plants to colonize the exposed lake beds belonged to the families Poaceae (grasses), Amaranthaceae (amaranths/chenopods) and Fabaceae (legumes), among others.

The sediment record from Lakes Metzabok and Tzibaná as well as testimonies of local Lacandon Maya inhabitants suggest that similar lake level lowering events occurred in the past. The hydrology of karst lakes is complex and unpredictable because multiple geological and hydrological factors control the water balance. The cause of this recent lake level lowering event remains unknown, but may be revealed by interdisciplinary studies of the limnology, paleolimnology, structural geology, geophysics, hydrology, geochemistry, genomics and geodesy of lakes and rivers in the region, as well as traditional environmental knowledge of the Lacandon Maya.

How to cite: Perez, L. and the Selva Lacandona science team: Ecological effects of sudden drainage of large karst lakes in the Lacandon Maya region, southern Mexico, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11490, https://doi.org/10.5194/egusphere-egu2020-11490, 2020.

In the current study the result of subfossil Cladocera analysis of the lake sediments from tree sites: Hinterste Mühle (H-M) (NE Germany), Rzecino (NW Poland) and Łęczyce (N Poland) of the Eemian Interglacial and the inferred environmental alterations are presented. The aim of the study was to reconstruct and compare the development of Eemian lakes located within the north of Poland and Germany as determined on the basis of the changes in subfossil Cladocera composition in the context of local conditions, climate change and natural evolutionary processes.

The studied reservoirs, fully developed during the Eemian Interglacial, were formed at the end of Late Saalian (MIS 6) and Early Eemian. The Hinterste Mühle profile is located in Mecklenburg-Western Pomerania. The site lies in the southeastern edge of the gravel pit, at about 48 m a.s.l. The Rzecino paleolake is located in the West Pomerania Lakeland (NW Poland), at an elevation of 104.5 m a.s.l. The Łęczyce palaeolake is located in northern Poland, on the northern slope of the Łeba river valley.

The subfossil Cladocera fauna from the H-M palaeolake is represented by 14 species belonging to three families. Three of them belong to a benthic group inhabiting mainly the bottom sediments, one to the open water zone, while the remaining species the dominant group occur among aquatic plants. Such a species composition marks a shallow water body or the littoral, macrophyte zone of a deeper lake. The Cladoceran fauna of deposits from the Rzecino paleolake are represented by 22 species that belong to four families. The majority of the remains consist of Chydoridae and Bosminidae. In the deposits, the ephippial eggs of the Daphnia longispina group, Ceriodaphnia spp., Chydorus spp., and Bosmina spp. are also identified. The subfossil cladoceran fauna of sediments in the Łęczyce profile is represented by 18 species that belong to four families. Most of the remains belong to the family of Chydoridae (13). Such species composition points to a deeper reservoir with a developed littoral zone with macrophytes.

Summing up, a similar pattern was observed in the research paleolakes related to the beginning of the existing of the lakes, their full development and ending time, different from the paleolakes found in the south, related to the location and more intense contact with cool air masses from Northern Europe.

How to cite: Niska, M., Hrynowiecka, A., Mirosław-Grabowska, J., Borner, A., and Sokołowski, R.: Eemian environmental changes recorded in the north located lakes (N Poland and Germany) - subfossil Cladocera data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20176, https://doi.org/10.5194/egusphere-egu2020-20176, 2020.

Evidence for global environmental and climate change-related loss of biodiversity is accumulating. Understanding the causes of species community change is thus essential for effective management and conservation policies. Nonetheless, disentangling the relative influence of the individual or multiple drivers determining the species communities is challenging, as ecosystems are simultaneously affected by variable drivers acting on different spatial and temporal scales. To this end, paleolimnological data may provide critical information on long-term community changes, species dominance shifts, and their underlying drivers. Natural forced changes in the aquatic environments can be used to study the response of biota to repeated fluctuations in essential key variables. In this study, we investigated the planktonic diatom communities in a continuous, 1.36 Ma sedimentary succession from ancient Lake Ohrid (North Macedonia/Albania). This is the oldest, continuously existing freshwater lake in Europe, acknowledged as a site of exceptional biodiversity and endemic species richness. An extended biogeochemical dataset from the DEEP site sedimentary record and previously-published variables representing global climate variability was used to: i) quantify the relative influence of individual environmental variables in governing species communities, and ii) disentangle the contribution of basin-scale environmental processes and global-scale climate variability in driving community patterns over time. The results show that the structure of planktonic communities was primarily determined by the basin-scale environment, particularly, nutrient availability, water temperature and water column mixing, but also local tectonic processes, since lake ontogeny. However, since the onset of the penultimate glacial period 0.185 Ma ago, global-scale climate variability became the principal drivers of the diatom community structure. Our proxy time-series illustrates how various factors at different spatial scales may determine the freshwater planktonic communities over geological time-scales. Extended periods of stable communities can be terminated by changes in climate, environmental conditions and/or lake ontogeny, leading to species extinctions and community turnovers. Thereby lake ecosystem structure and functioning are affected and effective management and conservation policies are required to minimize additional anthropogenic change-related loss of biodiversity. 

How to cite: Cvetkoska, A., B. Van de Waal, D., H. Donders, T., Jovanovska, E., Levkov, Z., Hauffe, T., M. Reed, J., Francke, A., Vogel, H., Wilke, T., Wagner, B., and Wagner-Cremer, F.: Basin- and global-scale environment alternately drive diatom community structure in ancient Lake Ohrid, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5849, https://doi.org/10.5194/egusphere-egu2020-5849, 2020.

Sunlight fuels the drawdown and evasion of carbon in shallow northern lakes. Amplified polar warming is altering the sunlit transport and transformation of aquatic carbon at an alarming rate entailing potential for climate feedbacks. We combined experimental and retrospective approaches to explore the synoptic interlinks between underwater light, aquatic carbon biochemistry, landscape carbon cycling and climate change in two shallow subarctic lakes with divergent light and carbon regime (a clear lake low in organic carbon and a dark organic rich lake). In situ enclosures (treatments under full sunlight, sunlight without the ultraviolet [UV] spectrum, no light) were first deployed on the lakes to decipher the effect of photochemical alteration on the spectral, elemental and isotopic properties of lake water organic carbon pools under short term (four weeks) exposure. We then focused on elemental, isotopic and spectral fingerprints archived in the sediments of the lakes to trace coeval variability in aquatic primary production, terrestrial carbon transport, and underwater light under centennial climate fluctuations. We observed distinct differences in carbon biochemistry between the experimental treatments illustrating the importance of sunlight, and particularly the UV spectrum, in shaping the carbon pools of the lakes already over short time scales. Over the past centennia, sediment biogeochemical composition carried signatures of change in carbon origins (algal vs terrestrial) and shifting underwater light regime. The results shed light on how climate change and sunlight shape carbon flows in shallow northern lakes over short and long time scales.

How to cite: Rantala, M., Kivilä, H., Meyer-Jacob, C., Wauthy, M., Rautio, M., Lami, A., Luoto, T., and Nevalainen, L.: Traces of sunlight in carbon biochemistry of shallow subarctic lakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15070, https://doi.org/10.5194/egusphere-egu2020-15070, 2020.

Mountain lakes are often remote, located in environments that experience cold temperatures, high incident solar and ultraviolet radiation, and prolonged ice and snow cover. They are, therefore, frequently dilute and oligotrophic. Together these factors can affect mountain lake ecosystem structure, diversity, and productivity. However, distant human activities resulting in atmospheric pollution, as well as more local disturbances, such as fish stocking, potentially increase nutrient inputs and alter mountain lake ecosystems. Our research addresses how these human activities have altered algal production in Uinta Mountain (Utah, USA) lakes. Sedimentary chlorophyll a and its derivatives were measured using visible reflectance spectroscopy in short sediment cores from a total of 12 lakes, including both alpine and subalpine lakes, to determine trends in algal production. All sediment cores were dated using ²¹⁰Pb and ¹⁴C dating, and the records were shown to extend back 300 to 500 years. Our results show that regardless of whether lakes were stocked or not, algal production remained virtually unchanged until 1950 when it increased dramatically in most lakes. The widespread distribution of the sites points to a regional stressor, such as atmospheric deposition of nutrients, as being the main cause for increased algal production. Additional analyses, including diatoms and C and N isotopes, measured in sediments from some lakes support this finding. The few lakes where algal production trends differed showed either that algal production had changed little overtime or that it was variable throughout the record. Although speculative, the lake that showed unchanged algal production is surrounded by a wetland that may have contributed nitrogen to the lake throughout the record meaning that additional nitrogen had little effect on algal production. Lakes with more variable algal production were subalpine lakes. The variable trend may point to more complex pathways and transport of nitrogen from the catchment to the lakes at lower elevation sites. Our findings show that remote mountain lakes, which typically are important water resources and biodiversity hotspots, are rapidly changing as a result of human activities, but not all of these lakes are responding in the same way. To effectively protect mountain lakes it will be important to identify and quantify influential factors affecting lake response to anthropogenic stressors.  

How to cite: Moser, K. A., Hundey, E. J., Sia, M. E., Doyle, R. M., Dunne, H., and Longstaffe, F. J.: Factors Leading to Increased Algal Production in Mountain Lakes: A Paleolimnological Perspective from the Uinta Mountains, Utah, USA, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5995, https://doi.org/10.5194/egusphere-egu2020-5995, 2020.

Lake sediments are globally important carbon sinks, and play a critical role in the global carbon cycle. Although the fate of organic carbon in lake sediments depends mostly on sedimentary microorganisms, the environmental controls on the microbial community structure in lake sediments are still poorly understood.

Here we investigate the relationships of lake trophic state, sediment redox chemistry, sediment organic matter (OM) sources and microbial community structure in sediment records across five lakes with different eutrophication histories and trophic states in central Switzerland. Our results show that, across all five lakes, bacterial and archaeal communities based on 16S rRNA gene sequencing analyses show similar sediment depth-dependent zonations at the phylum- and class-level, which appears to be primarily driven by vertical distributions of electron acceptors and secondarily by differences in the contributions of aquatic and terrestrial OM revealed by biomarkers. Yet, there are clear differences in microbial communities between lakes, most notably the higher abundances of putatively aerobic nitrifying Bacteria (Nitrospirae) and Archaea (Marine Group I, Thaumarchaeota) in anoxic sediments of oligotrophic Lake Lucerne. Furthermore, at the level of Zero-radius Operational Taxonomic Unit (ZOTU), eutrophication-related trends are more pronounced, in which microbial communities in the sediments of eutrophic lakes are more similar and share more ZOTUs with each other than with the oligotrophic lake. Notably, deep sediment layers of presently eutrophic lakes that were deposited prior to the era of eutrophication show high similarities in bacterial communities to equivalent depths in the oligotrophic lake. By contrast, archaeal communities are clearly differentiated according to trophic state only in recently deposited sediment layers, and independent of trophic state converge toward high similarities over time.

Our study indicates a significant role of trophic status in driving lacustrine sediment microbial communities and reveals fundamental differences in the temporal responses of bacterial and archaeal communities to anthropogenic eutrophication.

How to cite: Han, X., Schubert, C., Fiskal, A., Dubois, N., and Lever, M.: Lake trophic states shape microbial community structure in sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9772, https://doi.org/10.5194/egusphere-egu2020-9772, 2020.

Many lakes in industrialised areas have undergone anthropogenically driven eutrophication and increases in pollution leading to decreased water and sediment quality. In some cases, these effects are enhanced by seasonally changing lake redox conditions that may act to concentrate potentially toxic elements sufficiently to exceed internationally recognised Sediment Quality Standards, impacting key species and jeopardizing water supply.  A combined, geochemical and sediment microfabric analysis is applied to reconstruct the history of cultural eutrophication and pollution in the North and South Basins of Windermere, England’s largest natural lake. We also document a record of seismicity and link increased sedimentation rates and sediment instability. The onset and development of eutrophication in Windermere occurred from the mid-19th to the early 20th centuries.  Raised lake productivity is indicated by an increase in sedimentary δ¹³C, and increased pollution by elevated sedimentary trace metals (Pb, Zn, Cu, Hg, and As), likely enhanced by incorporation and adsorption to settling diatom aggregates, preserved as sedimentary laminae. In the South Basin of the lake, contemporaneous increasing sediment δ¹⁵N values also occur in step with increasing Zn, Hg, Cu from this time, linking metal enrichment to the input of isotopically heavy nitrate (N) from anthropogenic sources including sewage. From around 1930, a decrease in Mn and Fe-rich laminae indicate reduced deep water ventilation, and increased incidence of sediment anoxia, being most intense in the deeper North Basin where benthic activity intermittently ceased. Strongly reducing conditions in the sediment promoted Fe and Mn reduction and the formation of unusual Pb-bearing barite, hitherto only described from toxic mine wastes and contaminated soils. In the North Basin cores a clay rich laminae dated 1979-1980 is shown to be a mass transport deposit linked to large scale slope failure likely caused by the 4.7 ML 1979 Carlisle earthquake. Slope failure was exacerbated by preconditioning principally by increased sedimentation as a result of anthropogenic activities. From 1980 there was a partial recovery in oxygenation with Mn and Fe rich laminae returning in some parts. But in the South Basin, the continued impacts of sewage discharge is indicated by elevated δ¹⁵N of organic matter. Imaging and X-ray microanalysis using scanning electron microscopy has enabled the identification of seasonal-scale redox mineralisation of Mn, Fe and Ba related to intermittent sediment anoxia. Elevated concentrations of Mn, Fe, Ba, and As also occur in the surficial sediment and provide evidence for dynamic redox mobilisation of potentially toxic elements that may be released to the lake waters. Concentrations of As, in particular, exceed international Sediment Quality Standards. These surface enrichments in As and other toxic elements may become more prevalent in the future with climate change driving lengthened summer stratification in the lake.

How to cite: Fielding, J., Kemp, A., Croudace, I., Langdon, P., Pearce, R., Cotterill, C., and Avery, R.: High resolution sediment microfabric and geochemical analysis reveals seasonal scale redox mineralisation, anthropogenic environmental change and pollution in England's largest natural lake - Windermere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-523, https://doi.org/10.5194/egusphere-egu2020-523, 2020.

Varved lake sediments are valuable archives for reconstructing climate and environmental change in the human habitat at seasonal resolution. However, it is still not fully understood which factors control varve thickness and, consequently, varve proxy records are differently interpreted with respect to their climatic significance. Here we present, for the first time, a dual lake monitoring in two lakes forming calcite varves to provide new insights into the seasonal depositional processes forming these varves. The study lakes, Tiefer See (TSK) in NE Germany and Czechowskie (JC) in N Poland, are located a few hundred km away from each other in the southern Baltic lowlands. This is an ideal test region for this investigation because it holds the major known geographical cluster of calcite varve producing lakes. The lake basins are different in morphology and bathymetry and, therefore, are ideal to investigate common processes and local differences of seasonal deposition. The monitoring setup in both lakes is largely identical and included instrumental observation of (1) meteorological parameters, (2) chemical profiling of the lake water column including water sampling and analyses, and, (3) sediment trapping at both bi-weekly and monthly intervals. Finally, we compared our six-year monitoring time series with varve micro-facies of sediments deposited during this time at the lake bottom. Based on this robust data-set, we present and discuss new findings with respect to the seasonal deposition of endogenic calcite varves, as well as their limnologic control factors.

How to cite: Roeser, P., Dräger, N., Brykała, D., Ott, F., Pinkerneil, S., Gierszewski, P., Lindemann, C., Plessen, B., Brademann, B., Kaszubski, M., Fojutowski, M., Schwab, M. J., Słowiński, M., Błaszkiewicz, M., and Brauer, A.: Differences in calcite varve formation discerned by a dual lake monitoring approach in the southern Baltic lowlands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12343, https://doi.org/10.5194/egusphere-egu2020-12343, 2020.

Earth’s climate underwent dramatic cooling throughout much of the Cenozoic, which has been linked to continental drift, mountain building, and the formation and expansion of ice-sheets in Antarctica and the Arctic. In particular, the India-Asia collision and uplift of the Tibetan Plateau (TP) have been posited as critical events responsible for increasing the rates of physical and chemical weathering on land, thereby decreasing the CO2 concentration of the atmosphere. The uplift of the TP ultimately led to the onset of the complexly coupled monsoon-arid environmental system in East Asia. Global-scale studies of Cenozoic deep-sea sediments and Quaternary ice cores indicate that, superimposed to the long-term cooling trend, climate variability at orbital-to-centennial time-scales is primarily induced by changing solar insolation and irradiance, and strongly modulated by complex internal land-air-ocean interactions. From the continental perspective, however, both the dynamics and impacts of long-term climate evolution and short-term climate variability remain poorly constrained due to the paucity of continuous terrestrial sequences spanning the entire Cenozoic.
The Weihe Basin is located in the monsoon-sensitive region to the north of the Qinling Mountains, a landform that constitutes the geographic and climatic boundary between northern and southern China. In the depocentre of this basin, a predominantly lacustrine sedimentary sequence with a thickness of >7 km, provides an unprecedented opportunity for: (1) reconstructing tectonic-to-millennial-scale climate changes from the Eocene to the present; (2) elucidating basin-mountain coupling processes; (3) assessing the effects of Cenozoic tectonic-climate interactions on the onset and evolution of the Asian paleomonsoon; and (4) investigating climatic/environmental impacts on the evolution of microbial communities. Importantly also, (5) sedimentary filling of the Weihe Basin can potentially yield unique high-resolution records of continental climate variability during high atmospheric CO2 periods of the Eocene, mid-Miocene, and Late Pliocene, and thus serve an analog for Earth’s near future climate.
The Weihe Basin Drilling Project (WBDP) proposes a two-phase drilling strategy to recover a complete as possible Cenozoic terrestrial sedimentary record from the eastern Weihe Basin depocenter. In the first phase (applied for here) we aim at producing a 3-km-long pilot sedimentary record (WBDP-1) to test the best suitable analytical approach and to reconstruct orbital-to-millennial-scale climate variability since the Late Miocene. In the second phase our aim is to produce a 7.5-km-long sedimentary record (WBDP-2) spanning the entire Cenozoic sedimentary infill of the Weihe Basin. The regional geological framework is well characterized through numerous exploration boreholes and detailed multichannel seismic reflection surveys. Scientific drilling operations will be accompanied by downhole logging, as well as on- and off-site analyses of the retrieved cores. The WBDP-1 borehole is expected to yield a world-class paleoclimate record for the last ~10 Ma and lead to fundamental advances in our understanding of multi-timescale climate variability and tectonic-climate monsoon linkages. The project will also enhance public awareness of human adaptation to Earth’s changing environment.

How to cite: An, Z., Molnar, P., Zhang, P., Vogel, H., Level, M., Garzione, C., Dodson, J., Sun, Y., Wiersberg, T., Dong, H., Feng, X., Song, Y., Chang, H., Qiang, X., Wang, X., Lu, H., Liu, X., Ai, L., and Sun, Y.: Weihe Basin Drilling Project (WBDP): Cenozoic tectonic-monsoon interactions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12774, https://doi.org/10.5194/egusphere-egu2020-12774, 2020.

Before the onset of the modern Amazon river system, north-western South America was shaped by an extensive wetland during the Miocene. This ‘Pebas mega-wetland’ kept a well renowned endemic mollusk and ostracod fauna, which initiated a persisting debate about marine ingressions reaching the center of Amazonia at that time. Due to high endemism, uniformitarian principles are hardly applicable to this biota but also other paleontological, sedimentological and geochemical information led to ambiguous paleoenvironmental interpretations. These results are based on ostracod and foraminiferal assemblages and the oxygen and carbon stable isotopy of their biogenic calcite from an outcrop at the cutbank of the Amazon river (NE-Peru, ~55 km S of Iquitos). While ostracods (e.g., Cyprideis) are able to calcify their carapaces along the entire salinity range, at least low saline conditions are a prerequisite for the biomineralization of calcareous foraminiferan tests. Hence, the finding of calcareous foraminifers (Ammonia, Elphidium), associated mainly with brackish water ostracods, indicates the presence of saline waters. In contrast, δ¹⁸O- and δ¹³C-analyses performed on co-occurring ostracod valves and foraminiferan tests yielded constantly very light ratios. Such values refer to a pure freshwater environment and are incompatible with the interference of isotopically heavier, marine waters or an evaporative stable isotope enrichment. Based on these opposing data, we hypothesize that the Pebas mega-wetland was episodically influenced by mineralized but isotopically light groundwater discharge. Possibly, the resulting specific hydrochemistry contributed not only to the evolution of the endemic Pebasian fauna but also facilitated the sporadic settlement of euryhaline foraminifers, which mimics short-lived marine incursions.

How to cite: Piller, W. and Gross, M.: Aquatic ecosystems in Miocene western Amazonia – marine ingressions vs. salt leaching, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5483, https://doi.org/10.5194/egusphere-egu2020-5483, 2020.

The Fucino Basin is the largest and probably the only Central Apennine basin hosting a thick, continuous lacustrine sediment succession documenting the environmental history from the Early Pleistocene to recent historical times. The basin is located downwind of the Italian volcanic districts (< 150 km), which makes it the best candidate available in the central Mediterranean to construct a long and continuous tephrostratigraphic and tephrochronological record. Tephrostratigraphic investigations conducted on a first core (F1-F3) revealed 21 tephra layers of different Italian volcaoes. Among them several widespread and well-dated key Mediterranean marker tephra layers (e.g., Neapolitan Yellow Tuff, Y-1, Campanian Ignimbrite, Y-7, X-5, X-6, and Taurano Ignimbrite) were recognized and allowed to date, together with ⁴⁰Ar/³⁹Ar ages directly obtained from the Fucino tephra layers, the record back to 190 ka.

Based on these promising results, a new drilling site with a lower sedimentation rate was targeted, bringing forth the ~98 m long F4-F5 record. In addition to the already recognised tephra layers occurring in the section that overlaps with core F1-F3, ~110 additional tephra and cryptotephra horizons were identified in the composite sediment succession of the F4-F5 record, providing new insights into the Italian volcanic history for the poorly explored interval beyond 200 ka.

Here we present the first tephrostratigraphic and tephrochronological results for this interval, which is dominated by eruptions from the Sabatini, Vulsini, Vico, and Colli Albani volcanoes. Several important known eruptions were identified and dated for the first time in distal settings: e.g., Canino (256.8 ± 1.1 ka), Tufo Giallo di Sacrofano (288.0 ± 2.0 ka), Magliano Romano Plinian Fall (315.0 ± 2.0 ka), Orvieto-Bagnoregio Ignimbrite (335.8 ± 1.4 ka), Villa Senni (367.5 ± 1.6 ka), Pozzolane Nere and its precursor (408.5 ± 1.3 ka, and 407.1 ± 4.2 ka, respectively). Finally, a tephra located at the base of the succession was directly dated by ⁴⁰Ar/³⁹Ar at 424.3 ± 3.2 ka, thus extending the record back to the MIS 12/11 transition (~430 ka).

Ongoing geochemical analysis, including trace elements, Sr and Nd isotopes, and ⁴⁰Ar/³⁹Ar dating of both Fucino tephra layers and potential proximal counterparts will help to reveal their volcanic sources and enable further tephrostratigraphic correlations supported by independent age determinations. These results will contribute towards an improved MIS 11-MIS 7 Mediterranean tephrostratigraphy, which is still poorly characterized and exploited.

The recognition and dating of the numerous tephra layers from the F4-F5 record can be directly combined to construct a comprehensive age-depth series of biogeochemical proxies and geomagnetic excursions derived from the lacustrine sediments, forming the backbone for an independent, radioisotopically anchored chronology for the F4-F5 multi-proxy record. Through paleoclimatic alignments and geomagnetic excursion synchronizations, the independent Fucino chronology can be propagated to the North Atlantic records, and possibly on a global scale, setting the framework for a better understanding of the spatio-temporal variability, magnitude, and different expressions of Quaternary orbital and millennial-scale paleoclimatic changes.

How to cite: Leicher, N., Giaccio, B., Wagner, B., Mannella, G., Monaco, L., Zanchetta, G., Scheidt, S., Regattieri, E., Nomade, S., Pereira, A., Palladino, D. M., Niespolo, E. M., and Renne, P. R.: Tephrostratigraphy and tephrochronology of a 430 ka sediment record from the Fucino Basin, central Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5126, https://doi.org/10.5194/egusphere-egu2020-5126, 2020.

Here we present the first Holocene-long continuous chronology of volcanic eruptions on Kerguelen archipelago, where no evidence of Holocene volcanic activity has been published so far. Our chronicle is based upon sedimentological, chronological and geochemical data form two sediment cores, taken in two different depocenters of a large lake, Lake Armor, located ca. 70 km away from the archipelago’s potentially active volcanic area. This allowed us to confidently attribute the origin of pumice-rich or ash-rich layers to contemporaneous volcanic eruptions. Altogther eight main eruptions, as well as three secondary ones, were here documented and dated, among which the youngest occurred during the Middle Age, between 890 and 980 AD. The oldest eruption is also by far the strongest one and deposited more  than 1.2m of up-to 3cm large pumices, 70 km away from the volcanic edifice. It occurred at the very beginnning of the Holocene (11 ka cal. BP), suggesting a climatic control after glacial retreat upon volcanic activity. Additionnal evidences from lake sediment and geological outcrops, both close to Lake Armor and in remote areas over Kerguelen mainland, open the future possibility of a better reconstruction of major eruptions deposit spreading and thus an assessment of their intensity. This established chronostratigraphy will be useful to synchronise paleoenvironment record at least at the scale of the archipelago as well as in surrounding marine areas where Holocene climate reconstructions are particularly sparse.

How to cite: Arnaud, F., Sabatier, P., Leloup, A., Servettaz, A., Moine, B., Develle, A.-L., Guédron, S., Perrot, V., Poulenard, J., Fanget, B., Malet, E., Støren, E., Reyss, J.-L., Le Viavan, N., Heirman, K., De Batist, M., Michel, E., de Beaulieu, J.-L., Vanderputten, N., and Bakke, J.: Etablishing the first continuous Holocene tephrostratigraphy on Kerguelen Archipelago, subantarctic Indian Oean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5782, https://doi.org/10.5194/egusphere-egu2020-5782, 2020.

During the retreat of a Würm ice sheet, numerous glacial paleolakes took place in the Swiss and French Jura. Two sites were investigated: the Amburnex Valley site (Switzerland), which evolved in well-developed peatland and the Lake Val (France), which is still persisted as a lacustrine system. During the Late Glacial period, both sites were glacial lakes characterized by a significant accumulation of lacustrine sediments.

Using a multiproxy approach, this project aims to reconstruct the paleoclimatic and the paleoenvironmental evolution recorded in lacustrine sediments and peatbog deposits since the last 13’000 years.

The Amburnex core (7m) exhibit a basal morainic deposit from the Würm period, overlain by three meters of lacustrine deposits and four meters of peatland deposits. The Lake Val core (4.5m) consists of the same lithological succession.

A multiproxy approach based on palynological analyses, grain-size analyses, mineralogical analyses (XRD) and geochemical analyses (TOC, Nitrogen, Phosphorus and Mercury contents; major and trace elements; organic carbon isotopes) have been used to characterize the hydrological and climatic fluctuations, the trophic level and the origin of organic matter in order to reconstruct the paleoenvironmental and paleoclimatic evolution of this area.

In the Amburnex site, the Bølling-Allerød, the Younger Dryas and the beginning of the Preboreal period have been recognized by palynological analyses and confirmed by carbon 14 dating. During the Oldest Dryas, oligotrophic conditions took place as suggested by the very low concentrations in nitrogen and organic matter. Then, during the warmer Bølling period, an enrichment in total organic carbon (TOC) associated with a decrease in phosphorus content are observed, implying the development of eutrophic conditions and maybe phosphorus recycling. Later in the Allerød period, low TOC and phosphorus contents, associated with varved carbonate deposits, indicate a return to more oligotrophic conditions. New organic matter enrichments are observed in the interval corresponding to the colder Younger Dryas period. These trends are quite consistent with those observed in the Lake Val and reflect significant changes in runoff and nutrient inputs at least at regional scale.

How to cite: Bomou, B., Zappa, D., Rachoud-Schneider, A.-M., Haas, J.-N., Gärtner, M., Spangenberg, J., Bichet, V., and Adatte, T.: Jura glacial lakes: a paleoclimatic and paleoenvironmental evolution since the Late Glacial Period., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14955, https://doi.org/10.5194/egusphere-egu2020-14955, 2020.

The sedimentary record of deep-water lakes is often used to investigate past climate and environmental change. Correct identification however, of the main controls driving the production and transport of sediment to the deepest parts of tectonically active basins is often challenging, especially when trying to differentiate autogenic from allogenic factors. This study focuses on the changes observed in a deep-water sedimentary system that evolved from mudstone-dominated to the development of a lacustrine sand-dominated channel-lobe distributary fan and back to mudstone deposition during the Pliocene climatic optimum in the Corinth Rift, Greece. This is a multidisciplinary study that involves the integration of sedimentology and structural geology with digital outcrop modelling, palynology, palaeomagnetology and geochronology.

The studied sedimentary system consisted of a coarse-grained delta (Mavro delta) that fed the deep-water Rethi Dendro Formation (RDF) in the Amphithea fault block during the Pliocene and Early Pleistocene. These syn-rift deposits were sourced from a major hinterland catchment, the Olvios catchment, draining the southern, fault-controlled margin of the rift. The depocentre was located at the exit of a structurally controlled sediment fairway, ~15 km from the source of sediment and ~12 km basinwards from the basin margin coastline. The stratigraphy of the RDF in the study area is well constrained due to the combination of detailed surface mapping and logging with LiDAR, photogrammetry and UAV surveys of large-scale exposures in the Sythas river valley. These were integrated with the information obtained from the analysis of rock cores obtained through wells drilled immediately behind the cliffs where the RDF is exposed. The Amphithea fault block has a half-graben configuration and tilting of the hangingwall was one of the main tectonic controls on the evolution of the depocenter fill. The stratigraphic interval considered in this study is ~130 m thick. It was deposited above a ~6° angular unconformity and it is composed predominantly of fine-grained hemipelagic dominated units, interrupted by the development of an ~30 m thick sandstone-dominated channelized lobe unit. Detailed palynological analysis of this interval shows significant changes in pollen and spore assemblages that are used to interpret the palaeoflora developed in the drainage catchments. The palynoflora in fine-grained hemipelagic intervals is dominated by temperate forests mixed with subtropical elements, whereas the channelized lobe unit is dominated by palynofloras typical of open herbaceous vegetation including steppic taxa, suggesting a dryer and cooler climate. The shift from forest- to herbaceous-dominated palynological assemblages is gradual, recorded from 5 m below the facies change marking the base of the channelized lobe unit.  In contrast, the top of the channelized lobe unit coincides with the abrupt change back to the forest-dominated pollen assemblage. The correlation between the establishment of a sand-dominated channel-lobe distributary fan in the basin floor with the predominance of open herbaceous vegetation is interpreted to reflect the highly erodible condition of land covered in this type of vegetation. In contrast, during periods when forests are dominant, erodibility decreases.

How to cite: Muravchik, M., Eliassen, G. T., Henstra, G. A., Gawthorpe, R. L., Mangerud, G., Kouli, K., Kranis, H., Skoutsos, E., Leeder, M., Andrews, J., and Mark, D. F.: Climate and tectonic modulation of sand delivery to deep water lakes in rift basins. Late Pliocene, Corinth Rift, Greece, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17438, https://doi.org/10.5194/egusphere-egu2020-17438, 2020.

The Crimean Peninsula has around 50 saline lakes, which formed during the Holocene marine transgression. These lakes are valuable archives of the Holocene sea-level changes in the Black Sea, but their chronologies and evolution remain largely unknown. This study presents reconstructions of evolution of the Lake Chokrak basin and its depositional environment during the last 8000 years. At present, the lake is hypersaline and separated from the Sea of Azov by a narrow sandbar. The environmental reconstructions are based on multi-proxy data including shell content, organic geochemical and x-ray fluorescence analyses and radiocarbon dating of an 11-m sediment core. The aim of the study is to provide new insights into the evolution history of the lake in the region where such data are limited. Based on the interpretation, the following succession of stages was recognized in the lake evolution. Around 8000 cal yr BP, an open relatively shallow marine embayment existed in the study area, which is evidenced by high contents of Mn, indicating well-oxygenated waters, and presence of shells of Cerastoderma edule, which is favoured by shallow calm waters. Lamination of the sediments during this stage indicates relatively stable marine conditions. A deeper transgressive stage is observed from 7000 to 6500 cal yr BP when waters became less oxygenated, the grain size decreased and laminations disappeared. Precipitation of carbonates at the end of this stage indicates seawater evaporation. A dry stage from 6500 to 6200 cal yr BP is characterized by further decrease in water level and precipitation of gypsum. Starting from 6200 cal yr BP, a renewed transgressive stage is observed with increased water oxygenation, accumulation of fine sediments and precipitation of carbonates. From 5400 to 5000 cal yr BP higher erosion is demonstrated by an increase in Zr, Ti, Rb and Si contents and occurrence of sand layers in the sediment core. After 5000 cal yr BP starts a dry stage of the basin, which is connected to the slower rate of the Holocene sea transgression. Precipitation of evaporites (carbonates, halite, gypsum) increased at this time and fine-grained clays accumulated in the basin. This stage is also characterized by virtually continuous presence of C. edule shells. Relatively high organic carbon content and C/N ratios imply increased input of terrestrial organic material throughout this stage. The infilling of the basin and formation of the sandbar started around 3000 cal yr BP when clay sediments intermixed with sand layers. A transitional stage from semi-open to closed basin lasted from 1400 to 800 cal yr BP and it is characterized by precipitation of evaporites and disappearance of shells. The current stage (from 800 cal yr BP to present) of the closed lake basin is characterized by sediment lamination, high precipitation of gypsum and potassium salts, and complete absence of molluscs due to high salinity of the brine. The obtained results show that hydrological regime and geochemical composition of the lake were influenced by complex interaction of climatic, local tectonic and eustatic factors throughout its history.

How to cite: Rohozin, Y. and Ljung, K.: Mid- and Late Holocene hydrological and geochemical changes in Lake Chokrak (NE Crimea), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-602, https://doi.org/10.5194/egusphere-egu2020-602, 2020.

In paper presented results of complex investigations of Lake Bannoe (53°34'40.5"N 58°38'05.0"E) and its sediments. The origin of the Lake is tectonic. Seismoacoustic investigations were carried out for choose the best places for coring with continuous sedimentation and avoid gas saturated sediments. 4 long cores of sediments (up to 5.5 meters) were collected with using special hydraulic corer.

To study the sediments, a set of methods was used including petromagnetic and paleomagnetic studies, the study of mineralogical and elemental composition. According radiocarbon dating the maximum age of samples is 12.5 thousand. The age of samples increases with depth naturally, which means we have continuous sedimentation without hiatus.

Measurements of magnetic susceptibility (MS), hysteresis parameters and thermomagnetic analysis were carried out to determine changes in magnetic mineralogy and sedimentation conditions. Thermomagnetic curves measured on Curie express balance, coercitive parameters on J-coercivity spectrometer and magnetic susceptibility on multi-function kappabridge MFK1-FA (AGICO). The elemental composition was studied on an S8 Tiger X-ray fluorescence wave dispersion spectrometer. X-ray diffraction was performed on a Bruker D2 Phaser for studying mineralogical composition.

Changes in the magnetic susceptibility along the section are not significant, which indicates the constancy of sedimentation conditions. Only lower part, below 4.7 meters, MS increasing which corresponds to big input of terrigenous material. Most common magnetic minerals of sediments are pyrite and magnetite. Main minerals are quartz, albite, mica, from 1.3 meters and below in sediments detected calcite and dolomite.

Obtained data from all methods (magnetic properties, minerology, elemental composition) used for preliminary paleoclimatic and paleoenvironmental reconstructions of South Ural region for last 12.5 kyr. According petromagnetic data there is no big changes in sedimentation conditions. Also elemental composition shows the same, no big changes. Bottom part of sediments core are consist of more coarse material this is reflected both in magnetic properties and in elemental composition.

This work was funded by the Russian Science Foundation under grant № 18-17-00251.

How to cite: Kuzina, D., Anastasia, Y., Danis, N., Pavel, K., Vadim, A., Bulat, G., and Georgii, B.: Complex investigation of Lake Bannoe sediments (South Ural, Russia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20024, https://doi.org/10.5194/egusphere-egu2020-20024, 2020.

Lake Baikal (Russia) is the World’s oldest and deepest lake, which has been formed within a recently active rift zone at the edge of Siberian platform. Active tectonics influences all subaqueous geological processes in the Lake area with sedimentation, in particular. Selenga River is the largest river flowing into Lake Baikal. The river carries a large amount of terrigenous material sourced from Siberian-Mongolian drainage basin. Selenga River forms a large delta and several deep-water fans in the Central and South Baikal basins. Large amount of supplied terrigenous material, high sedimentation rates, steep slopes of the Baikal basins and active tectonic are favorable factors for the development of gravity-driven sediment transport processes.

A new large depositional system, named the Khuray deep-water fan, was discovered and studied since 2014 in the deep part of Lake Baikal during six Class@Baikal Project expeditions. It is located at the south-west of the Central basin of Lake Baikal, where it occupies a narrow, SW-NE extended area of about 1500 square km. Several 2D seismic surveys and bottom sampling campaigns were run during the expeditions in this area ranging in water depth from 800 to 1580 meters. A comprehensive set of collected geophysical and geological data provided important insights on the architecture of the Khuray lacustrine deep-water depositional system.

The system is fed by the Kukuy canyon, which is incised into the north part of the Selenga delta-front. In its upper reaches, immediately beyond the mouth of the Kukuy canyon, the Khuray system is represented by a set of meandering channels forming typical deep-water channel-levee complexes, which are well-expressed in bottom topography. The central part of the system develops over a large uplifted fault block, which is separated from of the rest of the Central basin by a well-expressed tectonic escarpment up to 80 m high. Within the block the system of the meandering channels is gradually replaced by a system of less distinct channels, which form a large braided channel complex less commonly observed in deep-water fan systems. At the distal part of the system, the channels become better expressed in bottom relief again and begin merging with each other forming, eventually, a single main channel. Another very interesting feature, a secondary canyon, is also observed at the distal part of the Khuray system. Once the small channels converge into the single one, it reaches a tectonic escarpment and forms a distinct erosional incision named the Khuray canyon. Several depositional lobes forming the lower reaches of the Khuray fan are found beyond the mouth of this secondary canyon, which is associated with a base of an active tectonic fault.

Active tectonic processes are believed to be the key factors responsible for the development of such complex architecture of the Khuray lacustrine deep-water depositional system comprising typical slope meandering channels, braided channel complex and several cascading canyons.

The reported study was funded by RFBR according to the research project № 18-35-00363.

How to cite: Solovyeva, M., Akhmanov, G., Khlystov, O., and Mazzini, A.: The Khuray deep-water fan: a beautifully complex lacustrine depositional system of Lake Baikal, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20977, https://doi.org/10.5194/egusphere-egu2020-20977, 2020.

The Tatra moraine relief and cosmogenic nuclide dating show glacier stabilizationand the maximum glacier extent in two phases,at26 – 21 ka and at 18 ka followed by a gradual retreat and  a termination of the glaciation during the Bølling/Allerød warming at 14.64 –12.9 ka (Makos etal., 2014). A renewed glaciation within the Younger Dryas (12.9 – 11.5 ka) formed smaller rock glaciers. This retreat was connected with the formation of the morainic, trough and cirque lakes and the beginning of light-grey silt sedimentation dated from 10ka to 16ka cal BP on the northern slopes of the Tatra Mountains and before 10ka cal BP on its southern slopes (Klapyta et al., 2016).

A new paleolimnic research led to a discovery of a cyclic fine laminated deposit in the four Tatra Mts. lakes. The laminae of thickness from 1 to 3 mm are built of couplets of light-coloured coarse detrital and fine dark-coloured laminae. Thicker light coloured laminae occasionally show a gradation ending in dark-coloured laminae. Laminae consist occasionally of low spherical angular grains of sand and gravel fractions, rarely up to size 10 mm which deformed underlying laminae. Light-coloured laminae are predominantly composed of quartz, followed by K-feldspar, plagioclase, mica, and clay-like particles. Dark-coloured laminae consist of clay-size clastic particles. These laminae were formed in cold, oxygen-rich, ultra-oligotrophic, slightly acid conditions in which the chironomids Pseudodiamesa nivosa and Micropsectra radialis-type dominated. We interpret these lamination as varves related to annual glacial melting. Once the valleys were ice-free, varve production stopped and a short deposition period of homogenous silt was replaced by gyttja. The radiometric C¹⁴ age dating shows the deglaciation in the Tatra Mts terminated at the beginning of the Early Holocene, around 10ka cal BP – 9ka cal BP.

The research was funded by APVV-15-0292 and the project Centre of Excellence for Integrated Research of the Earth's Geosphere, ITMS 26220120064.

Klapyta P., Zasadni J., Pociask-Karteczka J., Gajda A., Franczak P., 2016. Late Glacial and Holocene Paleoenvironmental records in the Tatra Mountains, East-Central Europe, based on lake, peat bog and colluvial sedimentary data: A summary review. Quaternary International 415: 126-144.

Makos M., Dzierzek J., Nitychoruk J., Zreda M., 2014. Timing of glacier advances and climate in the Tatra Mountains (Western Carpathians) during the Last Glacial Maximum. Quaternary Research 82: 1-13.

How to cite: Ramachandran, D., Pipík, R., Chamutiová, T., Žatková, L., Vidhya, M., Milovský, R., Milovská, S., Starek, D., Šurka, J., Uhlík, P., Bitušík, P., Hamerlík, L., and Biroň, A.: Fine laminated clastic deposits revealing the delay of the deglaciation timing in the High Tatras Mts. (Central Europe) to Early Holocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1104, https://doi.org/10.5194/egusphere-egu2020-1104, 2020.

Lake Urmia, in northwest Iran, is the largest saline lake in the Middle East with surface area of 5000 km². Despite its potential as an archive of paleoclimate and paleoenvironmental information for Southwest Asia there has been no molecular organic geochemical investigation or precise dating of these sediments, especially for the Holocene. This study used multi-proxy analysis combining sedimentological, bulk and stable organic geochemical and compound specific stable isotopes along with high-resolution radiocarbon dating on organic and carbonate material to understand the Holocene climate and environmental variability in SW Asia.

The age model based on sixty calibrated radiocarbon dates shows variation of sedimentation rates between early and middle Holocene and a sudden increase in late Holocene. The most prominent change, at 4.3 Ka, closely corresponds to the well-documented 4.2 ka event (Medieval Optimum) in the Mediterranean and Middle East.

We used compound-specific hydrogen isotope ratios (δD) in long chain n-alkanes and n-alkonic acids as paleohydrological proxy. The fact that Urmia Lake is large and little affected by in-situ production of iso-GDGTs from methanogenic Euryarchaeota makes the measured TEX86 proxy reliable. Therefore, we used this proxy to reconstruct the Holocene paleotemprature.  The analyzed record reveals multi-decadal to centennial pacing of paleoclimate and paleoenviromental changes, with most prominent events recorded at 8.1, 4.3 and 2.5 ka BP.

How to cite: Haghipour, N., Hunziker, D., Darvishi, J., Mohammadi, A., and Eglinton, T. I.: Holocene paleoclimate and environmental reconstruction from Urmia Lake sediments in southwest Asia , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7726, https://doi.org/10.5194/egusphere-egu2020-7726, 2020.

During the “Paleoanthropocene”, humans have become one of the major factors affecting Earth surface processes, with intensified soil erosion being one of the most notable human-induced process. Especially semi-arid regions are vulnerable to human-induced soil erosion and landscape changes, which is particularly true for the Mongolian Altai, where extensive pastoralism and the rise of nomadic empires strongly influenced landscape changes. So far, only little is known about the impact of humans in the Mongolian Altai and whether landscape changes are naturally or human-driven. Therefore, our study investigates a 5 ka sediment core from Lake Khar Nuur, which is located at ~2500 m a.s.l. in the Mongolian Altai. More specifically, we carried out a biogeochemical multi-proxy approach to disentangle between natural and anthropogenic signals in the Khar Nuur sediments, which includes extensive ¹⁴C-dating, XRF analyses, CNS analyses and their stable isotopes, and fecal sterols.

For the 5 ka sediments from Khar Nuur, XRF, C_org and bulk δ¹³C results show alternating phases of in-situ produced aquatic sediments/organic material versus increased terrestrial input from the catchment. Since no hardwater effect is observed for Khar Nuur sediments, phases of dominated in-situ aquatic production (i.e. high Ca/Ti ratios, higher C_org and positive bulk δ¹³C values) gave ¹⁴C-ages close to the timing of sediment deposition/biomass formation. In contrast, during phases of increased terrestrial input (i.e. low Ca/Ti ratios, low C_org and negative bulk δ¹³C values), ¹⁴C-ages become successively older and show larger age offsets compared to their timing of deposition in the lake. Thus, clear evidence is given that old organic carbon became mobilized from the catchment soils by increased soil erosion during three terrestrial phases from ~4.3 to 3.7 cal. ka BP, ~3.2 to 2.8 cal. ka BP and ~2.0 to 0.7 cal. ka BP. Abundances of fecal sterols start to increase at ~2 cal. ka BP, and human and herbivore feces strongly increase until ~1 cal. ka BP. This increase in fecal sterols falls directly into the last erosive phase between ~2.0 to 0.7 cal. ka BP and indicate that soil erosion during that time was mainly human-induced by increased pastoralism. Moreover, beginning human presence at ~2 cal. ka BP corresponds to the Xiongnu (the Huns), whereas the strongly increased anthropogenic activity in the region at ~1 cal. ka BP falls into a period where Turks, Uighurs and Mongols are present in western Mongolia and the Altai. Thus, soil erosion and landscape changes in the Mongolian Altai are strongly driven by the rise of pastoralism and nomadic empires during the late Holocene.

How to cite: Bliedtner, M., Strobel, P., Struck, J., Enyedi, B., Bromm, T., Glaser, B., Salazar, G., Szidat, S., Lloren, R., Dubois, N., and Zech, R.: Human-induced soil erosion and landscape changes in the Mongolian Altai – a biogeochemical multi-proxy approach from Lake Khar Nuur, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9608, https://doi.org/10.5194/egusphere-egu2020-9608, 2020.

High-resolution records of lake-level changes are crucial to elucidate the impact of local and global climatic changes in lacustrine basins. The Late Quaternary evolution of the Dead Sea has been characterized by substantial variability apparently linked with global climatic changes, beign subject of many research efforts since decades. Previous studies have defined two main lake phases, the Lake Lisan and the Dead Sea, the earlier was a highstand period that lasted between ~70 and ~15 ka, the  latter was the lowstand period that persisted until the present. Here we focus on the switch between Lake Lisan and Dead Sea studying fossil lake shorelines, a sequence that comprises dozens of levels exposed along the rims of the Dead Sea, containing abundant fossil stromatolites that we dated by mean of radiocarbon and U-decay series. We determined 90 radiocarbon and 35 U-Th ages from stromatolites from almost every shoreline level. We compared U-Th and radiocarbon ages to estimating a radiocarbon reservoir between 0.2 and 0.8 ka, used to correct the remaining radiocarbon ages before calibration. The resulting ages range between ~45  and ~20 ka. Dating was complemented with analysis of stable oxygen and carbon isotopes. Furthermore, we applied a distributed hydrological balance model to constrain past precipitation and temperature conditions. Our results suggest that the duration of the last Lake Lisan highstand was shorter than previously estimated. Taking this at face value, the switch between Lake Lisan and Dead Sea occurred at ~28 ka, ~10 ka earlier than previously suggested. Oxygen and carbon isotopes show a consistent pattern, displaying a switch between wet and dry conditions at ~28 ka. Preliminary results from the hydrological model indicate a much stronger sensitivity of the lake level to precipitation amounts than to air temperature. From our results we can’t observe a clear link between global temperature variations and lake-level changes in the Lisan/Dead Sea lakes. Similar non-linear response to northern hemisphere climatic changes have been also documented in Holocene Dead Sea paleoclimatic records, suggesting that global climatic variations may led to variable lake-level responses. The results of this study adds further complexity to the understanding of factors controlling climate variability in the Dead Sea.

How to cite: Jara-Muñoz, J., Agnon, A., Fohlmeister, J., Mey, J., Frank, N., Plessen, B., Schroeder-Ritzrau, A., Garcin, Y., Darvasi, Y., Melnick, D., and Strecker, M.: Lake level changes in the Dead Sea during the late Pleistocene recorded by fossil lake shorelines, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5669, https://doi.org/10.5194/egusphere-egu2020-5669, 2020.

Sedimentary records from the Dead Sea constitute unique paleoclimatic archives that enable investigating the response of environments to climatic changes. Large lake-level fluctuations (>100 m) occurred during the past glacial-interglacial cycles due to reorganizations of the hydroclimatic regime and drastically modified the morphology of the drainage area. We aim here to reconstruct past sedimentary dynamics at times of varying lake level to gain insights into paleoclimate and landscape evolution.

For this study, we have compared present-day surface sediments (fluvial and soil sediments) retrieved on both the eastern Jordanian and western shores of the present Dead Sea with downcore sediment archives including the ICDP Dead Sea Deep Drilling Program Site 5017-1. Streams originating from various parts of the watershed can be distinguished by their grain-size distribution, with northern and south-western streams having generally finer grain-size modes when compared with streams from the eastern side. We find that all modes identified in the fluvial sediments were present in the ICDP downcore samples from the last deglaciation, when lake levels were up to 250m higher than today. This suggests that the whole watershed contributed to the sediment input at that time. In contrast, Holocene sediments from the deep core and shore deposits are enriched in fluvial particles showing similar grain-size modes as the northern and south-western streams. This suggests that these regions were prime sediment sources during lower lake-level stands. An additional mode, tentatively related to aeolian particles, was also identified in the Holocene samples, pointing to the remobilization of deposited dust in the watershed or to a more arid regional climate.

Our results provide a first synoptic view on sedimentary dynamics in the Dead Sea watershed and help to relate sediment provenance to the drainage morphology and paleo-hydrological regimes. They constitute a solid basis for further assessment of sedimentary provenance using geochemical indicators.

How to cite: Blanchet, C., Jurikova, H., Fusco, J., Tjallingii, R., Schwab, M., Andermann, C., and Brauer, A.: New insights on sediment provenance in the Dead Sea since the last glacial maximum using grain-size distribution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20276, https://doi.org/10.5194/egusphere-egu2020-20276, 2020.

Recording and analyzing how climate change impacts flood recurrence, basin erosion, and sedimentation can improve our understanding of these systems. The aragonite-detritus laminae couplets comprising the lacustrine formations that were deposited in the Dead Sea Basin are considered as faithful monitors of the freshwater supply to the lakes. We count a total of ~5600 laminae couplets deposited in the last 45 kyr (MIS3-MIS1) at the Dead Sea depocenter, which encompass the upper 141.6 m of the ICDP Core 5017-1. The present study shows that aragonite and detritus laminae are thinner and occur at high frequency during MIS 3-2, while they are much thicker and less frequent during MIS 1. By analyzing multiple climate-connected factors, we propose that significant lake-level drops, enhanced dust input, and low vegetative cover in the drainage basin during the last deglaciation (22-11.6 ka) have considerably increased erodible materials in the Dead Sea watershed. We find a decoupling existed between the significant lake-level drop/lake size reduction and lamina thickness change during the last deglaciation. We argue that during the last glacial and the Holocene, the variation of lamina thickness at the multiple-millennium scale was not controlled directly by the lake-level/size change. We interpret this decoupling implying the transport capacity of flash-floods is low and might be saturated by the oversupply of erodible materials, and indicating a transport-limited regime during the time period. We suggest that the observed thickness and frequency distribution of aragonite-detritus laminae points to the high frequency of small-magnitude floods during the last glacial period, in contrast to low frequency, but large-magnitude floods during the Holocene.

How to cite: Waldmann, N., Lu, Y., Bookman, R., and Marco, S.: A 45 kyr laminae record from the Dead Sea: Implications for basin erosion and floods recurrence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6544, https://doi.org/10.5194/egusphere-egu2020-6544, 2020.

The drainage basin of the Dead Sea is the largest hydrological system in the Levant and spans across the boundary between the sub-humid to semi-arid Mediterranean and the arid to hyper-arid Saharo-Arabian climate zones. As a terminal lake, precipitation changes due to climatic variations result in extensive fluctuations of lake level and sediment deposition.

A unique sediment record from the deepest part of the Dead Sea Basin was obtained as part of the ICDP Dead Sea Deep Drilling Project. Here we analyze the partially annually laminated sediments of Core 5017-1-A between 88.5-99.2 m core depth, which comprise the period between ~16.5 and ~11 ka and document a lake level drop of ca 160 m. In the sediments of Core 5017-1-A, this marks the transition from MIS2 aad (alternating aragonite and detritus) sediments to MIS1 halite deposits and ld (laminated detrital marl) sediments, coinciding with increased drying in the Dead Sea watershed.

Microfacies analyses show the occurrence of several lithological facies that accumulated during MIS2: aad, gd (massive gypsum deposit within marl), native sulfur concretions (associated with greenish colored aad), mtd (mass-transport deposits, typically graded) and homogenites consisting of clay and silt. Further, flood layers have been identified, potentially indicating rainstorms associated with specific eastern Mediterranean synoptic systems. To complement the microfacies analyses, XRF scanning provides continuous Ti/Ca and S/Ca records to reconstruct relative detrital input and gypsum occurrence, respectively. Additionally, to study potential early signs of hydroclimatic change, the deep lake sediments are correlated to the Lisan Formation of the marginal Masada outcrop using distinct gypsum marker layers, indicative of pronounced lake level drops. However, due to a significant lake level decline, the Masada outcrop sediments terminate at around 14.5 ka and the subsequent lake level lowering is solely recorded in the deep lake sediments.

This study was funded by the German Science Foundation (DFG Grant BR 2208/13-1/-2). Further, it is a contribution to the Helmholtz Association (HFG) climate initiative REKLIM Topic 8 “Abrupt climate change derived from proxy data”.

How to cite: Schwab, M. J., Müller, D., Neugebauer, I., Tjallingii, R., Ben Dor, Y., Enzel, Y., and Brauer, A.: Changes in hydroclimate during last deglaciation lake-level fall in the Dead Sea sediment record, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7372, https://doi.org/10.5194/egusphere-egu2020-7372, 2020.

Tropical karst Lakes Metzabok (550 masl, surface area = ~77 ha, z_max = 25 m) and Nahá (832 masl, surface area = ~57 ha, z_max = 36 m) are located in the Lacandon Forest, in the state of Chiapas, southern Mexico. The region is characterized by high aquatic and terrestrial biodiversity. We generated high-resolution paleoclimate and paleoenvironmental records that span the last ~500 years, using invertebrate remains (ostracodes and gastropods) and geochemical variables (elemental and mineralogical contents) in sediment cores from the two water bodies. We collected a short sediment core from each lake (Metzabok = 46 cm, Nahá = 60 cm) and analyses were carried out at 1-cm intervals. Uppermost sediments in the cores were dated using ²¹⁰Pb and ¹³⁷Cs, and deeper deposits were dated by ¹⁴C. Ostracodes and snails were identified to species level and their abundances were quantified. Concentrations of Ti and Fe were determined by portable XRF. The geochemical record reveals information about past climate variability, human-mediated erosion and transport of terrigenous elements. Changes in ostracode and gastropod assemblages mainly reflect past lake level fluctuations and changes in water conductivity. The dominant ostracode species was Cytheridella ilosvayi and the most common gastropod is Aroapyrgus sp., indicative of water depths ≤40 m and low water conductivity, respectively. Analysis of the ecological distances between samples suggests that Lake Metzabok is unstable, with frequent ecological changes equal to or greater than 50% of the community. These changes may have resulted from dramatic environmental differences associated with hydrological dynamics during dry and rainy seasons. The Nahá record presents two environmental conditions, i.e. periods of high stability and periods of change, when the system was in transition from a dry period to a wetter one, or vice versa. Despite differences between the two lakes with respect to elevation, size, depth, and seasonal dynamics, both records contain evidence of droughts ca. 300 and 200 yr BP, during the Little Ice Age. Whereas both records show a long-term tendency towards higher moisture conditions, the high-resolution of our study enabled us to detect fluctuations between dry and wet periods over the last 500 years that previous studies failed to recognize.

How to cite: Rubio Sandoval, K. Z., Correa-Metrio, A., Franco-Gaviria, J. F., Schwalb, A., Hoelzmann, P., Brenner, M., Blaauw, M., Kenney, W., Curtis, J., and Pérez, L.: A 500-year record of paleoclimate and paleoenvironment from the Lacandon Forest, southern Mexico , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10897, https://doi.org/10.5194/egusphere-egu2020-10897, 2020.

Comparison of varve preservation and characteristics between remote and urban lakes in Finland

Sarianna Salminen¹, Mikko Uotinen¹, and Saija Saarni²

¹Department of Geography and Geology, University of Turku, Finland

²Ecosystems and Environment Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki, Finland

The occurrence of varved sediments in Finnish lakes is known to be dependent on certain features, such as morphometry of the lake and its catchment. However, varve preservation triggered by recent hypoxia has been observed in Finnish lakes of which sediments are not naturally laminated. In these lakes human-induced eutrophication and hypoxia might have been the major factor triggering varve preservation.

Here we compare varve preservation, varve characteristics, and varve qualities between one remote and naturally laminated (Lake Lehmilampi in Eastern Finland) and two lakes close to urban areas (Lake Vesijärvi in Southern Finland and Lake Kallavesi in Eastern Finland) with recent start of varve preservation.

Surplus of organic matter leading to hypoxia seems to have triggered the start of varve preservation in Lake Vesijärvi and possibly in Lake Kallavesi in the 20th century. In these two lakes several varve microfacieses were identified representing human-induced changes in the catchment. In the remote Lake Lehmilampi sedimentation rate is lower compared to the two urban lakes and the number of identified microfacieses is lower. The results suggest that in these three lakes varve characteristics, varve quality, and the cause of varve preservation as well as the continuity of varve preservation differ between lakes as a result of regional and local factors. In Lake Lehmilampi varve preservation seems to be dependent on lake and catchment morphometry as well as climate, whereas in Lake Vesijärvi and Lake Kallavesi varve preservation mainly seems to be dependent on anthropogenic factors. For instance, in Lake Vesijärvi rehabilitation actions seem to have affected varve preservation turning the sediment non-laminated. Furthermore, varve characteristics and quality seem to be sensitive to climate in Lake Lehmilampi, whereas in Lake Vesijärvi and Lake Kallavesi they correspond to anthropogenic changes.

How to cite: Salminen, S., Uotinen, M., and Saarni, S.: Comparison of varve preservation and characteristics between remote and urban lakes in Finland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8943, https://doi.org/10.5194/egusphere-egu2020-8943, 2020.

Inland waters are sites of active carbon (C) processing and transport along the land to ocean aquatic continuum (LOAC) that need to be accounted for closing the global C budget^1,2. However, monitoring data are lacking and do not extend back as far as few decades, limiting our comprehension of the LOAC C cycle for the last centuries. Lake sediments provide a key archive for assessing C transport and transformation that occurs in lake catchments. Here, the analysis of large numbers of samples was performed on 420 lakes sediment records of the world to assess C burial rates and sources during the last 300 years. C and N (organic and mineral forms) on discrete samples were analyzed using a Variomax elemental analyzer to assess total C sequestration by lakes, C sources, and long-term changes in the contribution of allochtonous vs autochtonous sources to C transfers in lake-watersheds. Continuous sediment records were generated using core scanners (i.e. micro-XRF) and computed tomography to provide near-annual trends on terrigenous elements, here used as proxies of allochtonous sources (e.g. Al, Ti, K, Fe), and Mn:Fe ratio to infer past oxygen conditions³. Our results suggest that establishing a morphology-relevant lake typology that better characterises the types and distribution of oxygen conditions and terrigenous supplies across our sites is therefore the first step in providing a more robust evidence base for explaining the spatial-temporal variation in lake C burial rates.

How to cite: Jenny, J.-P., Niemman, C., Francus, P., Noren, A., and Carvalhais, N.: A meta-analysis of paleolimnological records reveals the sensitivity of lacustrine carbon burial rates to carbon sources and preservation conditions during the Anthropocene , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11679, https://doi.org/10.5194/egusphere-egu2020-11679, 2020.

The Gulf of Corinth is one of the World’s fastest extending continental rift basins. During the Late Pleistocene, it alternated between marine and lacustrine conditions due to climate-driven sea-level fluctuations connecting or isolating/semi-isolating it from the open ocean. Core from IODP Expedition 381 (Corinth Active Rift Development) provide a continuous record of depositional processes operating within this deep-water rift and the interaction of tectonic and climate drivers controlling deep-water deposition over the Middle to Late Pleistocene. Subaqueous sediment density flows affect the Gulf of Corinth and are classified either by physical flow properties and grain support mechanisms or by depositional processes. Existing classifications mainly describe deposits from decimetre to 10’s of meter scale with an emphasis on sandy beds. Thinner (millimetre to centimetre scale) and finer (muddy to sandy) subaqueous sedimentary density flows beds are understudied. Low energy flows and tail of flow processes need a better understanding and are the target of this work. The aim of this study is to characterise the variability of fine-grained subaqueous sedimentary gravity flow deposits and the controls on their development based on core data from Site M0079 (IODP Expedition 381).  This site is located in the deepest part of the Gulf of Corinth (857 m water depth), in the most distal part of the sediment routing system. Analyses were performed within a 100 m interval covering Marine Isotope Stages 6 and 7 (from ~130 to ~250 ka). Detailed, sub-centimetre visual logging recorded over 2 000 beds classified according to (1) the presence/absence of a coarse base, (2) the grain-size (silty or sandy) of the base (if any), (3) the presence/absence of laminations within the muddy intervals, (4) sedimentary structures. The bed types reflect the diversity of the sedimentary processes and the subaqueous sediment density flows are thus organised within the depositional model. Bed frequency analysis provides insight into the variability between marine and lacustrine conditions. Relative chemical composition obtained from high resolution (2 mm) X-ray fluorescence scanning is used: (1) to examine the interactions between tail of the flow and background sedimentation in the basin and (2) to assess the provenance of the sediments.

How to cite: Fabregas, N., Gawthorpe, R., Ford, M., Muravchik, M., Pechlivanidou, S., and Röhl, U.: Variability of fine-grained basin floor turbidites and evaluation of controls on their development: Late Pleistocene, Gulf of Corinth, Greece, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8560, https://doi.org/10.5194/egusphere-egu2020-8560, 2020.

The Lagoa de Santo André is a coastal lake located ca. 80 km south of Lisbon at the Atlantic coast of Portugal. The region is highly vulnerable to earthquake-triggered tsunami events due to its exposure to the very active tectonic boundary between the Eurasian and the African plates. Despite several natural and artificial breaches of beach barrier in the past, the lagoon still represents an appropriate geo-bio-archive for reconstructing the Holocene palaeoenvironmental evolution. For this purpose, a 10-m-long sediment core was taken from the centre of the lake by using a floating platform. Sedimentological, geochemical and micropalaeontological analyses were performed in order to unravel the former geological and climatic conditions, and to identify short-term events like tsunamis or storm surges that might have crossed or breached the shielding barrier, leaving their footprint in the sedimentary record of the lagoon.

The sediment core covers the palaeoenvironmental evolution of Lagoa de Santo André for at least the last eight millennia. The sandy deposits of the lowermost part of the core most likely represent the littoral phase of a palaeo-beach that had developed when the postglacial marine transgression had reached the area. Above alternating layers indicate varying environmental conditions that are characterised by peat growth, stagnant-water areas and intercalating sand layers that deposited during disconnections from and reconnections with the open sea. Since 3000 BC at the latest, the longshore transport had formed a beach barrier that separated the coastal lake from the open sea. As yet no deposits of an extreme wave event have been detected. However, the ongoing microfaunal analysis will clarify, if sudden changes of the salinity have occurred due to significant saltwater intrusions, which would hint at potential extreme wave events.

How to cite: Frank, S., Laermanns, H., Pint, A., Wagner, B., Bellanova, P., Feist, L., Mathes-Schmidt, M., Reicherter, K., and Brückner, H.: Lagoa de Santo André - The Holocene evolution of a coastal lake at the Atlantic coast of Portugal, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16826, https://doi.org/10.5194/egusphere-egu2020-16826, 2020.