SSP3.1

This study aims to reconstruct the paleoenvironmental and climatic conditions affecting the Levantine corridor during the early Pliocene. For the purpose of this study, a ~20 m continuous core sequence was retrieved out of the ~200 m long, tilted Erk el Ahmar sequence previously dated by cosmogenic isotopes to ~3.5 Ma. The record include intercalating units consisting of sands, silts, and clays that were sampled in high resolution in order to analyze a variety of sedimentological and geochemical proxies of past climate and environmental changes. We present new preliminary, high-resolution sedimentological (laser diffraction granulometry), petrophysical (magnetic susceptibility) and compositional (X-ray fluorescence) data along with accompanying statistical analysis performed with an advanced suite of data-science tools. These results reveal new cycles of environmental change in the area, which appears to be orbitally controlled, and include dramatic changes also indicated by discrete strata of fossil fragments. Moreover, cycles of deposition can also provide hints on the major hydrological controlling mechanisms. This project provides new light into favorable conditions for the subsistence of perennial lake environments in the Levantine Corridor, which in turn may have facilitated faunal migration between Africa and Eurasia.

How to cite: Greenlee, J., Dean, S., and Waldmann, N.: Paleoenvironmental reconstruction of the central Levantine Corridor during the Pliocene: insights from lacustrine settings, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15832, https://doi.org/10.5194/egusphere-egu21-15832, 2021.

Sediments deposited in Lake Chala constitute a high-resolution archive of past climate and environmental change in equatorial East Africa spanning two glacial-interglacial cycles. To correctly interpret the proxy records it contains, it is crucial to understand the evolution of lacustrine sedimentation in this volcanic crater basin since its formation on the lower south-eastern slope of Mt. Kilimanjaro. A dense grid of 37 km high-resolution seismic-reflection profiles allowed the reconstruction of the depositional history of Lake Chala. The seismic-stratigraphic sequence comprises sixteen distinct and finely-stratified units (U1-U16, youngest to oldest), grouped into five major depositional stages. Depositional stage I (U16, ~243-198 ka) marks the initiation of sedimentation in the originally ring-shaped depositional area surrounding two central tuff cones emerging from the basin floor and is characterized by a high rate of sediment accumulation and frequent occurrence of mass-wasting events (MWEs) under conditions of a relatively low lake-surface level compared to today. Depositional stage II (U15-U12, ~198-114 ka) represents the onset of basin-wide sedimentation above the central tuff cones, implying a higher position of the lake surface, less sediment focusing, and a shift to more strictly hemipelagic sedimentation. Multiple large-scale slope failures occurred around the basin periphery accompanying the progressive rise in lake level. Depositional stage III (U11-U8, ~114-97 ka) represents the development of a relatively flat lake floor under a significantly lower lake level, with evidence for strong sediment focusing implying accelerated sediment accumulation in central bottom areas. Depositional stage IV (U7-U4, ~97-20 ka) is again characterized by largely undisturbed hemipelagic sedimentation under mostly high lake-level conditions. However, frequent occurrence of mass-wasting events (MWEs) after ~48 ka resulted in the development of a longer, more gentle bottom slope towards the basin center. Depositional Stage V (U3-U1, ~20 ka BP to Present) represents the most recent period of basin evolution, during which the frequent occurrence of basin-focused sedimentation under a fluctuating lake surface level contributed to the establishment of the present-day very broad and flat basin floor of Lake Chala. Extrapolation of sedimentation rates established for the uppermost part of the sediment sequence, supplemented with basin-morphometric inferences derived from the successive depositional stages, yields an estimated age of ~243 ka for the oldest sediments in Lake Chala.

How to cite: Maitituerdi, A., Van Daele, M., Verschuren, D., De Batist, M., and Waldmann, N.: Depositional history of Lake Chala (Mt. Kilimanjaro, equatorial East Africa) from high-resolution seismic stratigraphy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14361, https://doi.org/10.5194/egusphere-egu21-14361, 2021.

In paleoclimate and paleoenvironmental studies, turbidites are usually considered as interruptions of the sedimentary sequence and therefore ignored. However, turbidites are composed of sediments from the (shallow) slopes along the lake’s periphery where fossil assemblages are often different to those in the deep basin. Turbidites may thus be valuable as carriers of this near-shore proxy information to a profundal core site. However, as turbidites are composed of reworked (older) sediments, their fossil content can only be exploited if their “mean time offset” can be readily estimated or ascertained to be minimal.

Several recent studies have shown that turbidites can indeed form as a result of surficial slope sediment remobilization, a process – independent of slope failure – in which only a thin veneer (20 cm) of surficial sediment is being remobilized, for example by earthquake shaking, and subsequently transported by a turbidity current. However, demonstrating that this process is active in a basin and determining the remobilization depth, is challenging, especially in the absence of slope cores. Here we study the turbidite record of the 215 m (~260 kyr) long composite core of Lake Chala in the framework of the ICDP project DeepCHALLA. We analyzed its sediment color at a 0.5-cm interval using a spectrophotometer and determined the average color for each of the 391 thickest turbidites (> 3 datapoints) in the L*a*b* color space. For the entire dataset, we performed a linear regression of the turbidite color against the average color of different intervals (2-55 cm) of laminated sediment below. For each combination of paired values, the highest R² values are found for the upper 7-15 cm of matrix sediment below the turbidites, which can thereby be interpreted as the average remobilization depth. These results are mainly based on the a* value, which shows (i) relatively poor correlations between adjacent intervals of laminated sediment (thereby not smearing the signal), and (ii) the most constant values in sediments from across the basin as determined by short-core transects. Depth-dependent variations of sediment color as determined from these transects further allows to estimate the water depth from which the turbidites were sourced.

Our results show that the sediments of most Lake Chala turbidites are 100-200 yrs older than the laminated sediments upon which they are deposited. We conclude that the turbidites can be used as ‘sampling windows’ to study temporal trends in macrofossils such as ostracods, chironomids and fish teeth, which are much more common along the basin periphery than in the deep basin.

How to cite: Van Daele, M., Swai, V., Van der Meeren, T., Wolff, C., Meyer, I., Waldmann, N., Lane, C., De Batist, M., and Verschuren, D.: Lake Chala turbidites produced by surficial slope sediment remobilization: A mechanism to bring near-shore macrofossils to the deep basin with only limited time offset, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12393, https://doi.org/10.5194/egusphere-egu21-12393, 2021.

Deep-water systems in active rift margins are complex, highly dynamic, and often characterised by short, steep source-to-sink configurations promoting high and sustained sediment supply to substantially underfilled, deep-water depocentres. The timing and character of coarse siliciclastic sediment delivery to deep-water environments in active rift basins is governed by complicated interactions of tectonics, climate, eustasy, and shelf process regime. However, existing sediment-supply models are largely geared towards longer term changes (~10⁶ yrs) in tectonics, or eustatic variability, with relatively limited consideration for higher order (10⁴-10⁵ yrs) changes in catchment sediment flux due to the difficulty in deconvolving controls at these timescales. In the case of deep-lacustrine, syn-rift systems, the excess accommodation resulting from substantial subsidence, limited storage in short or absent shelves, and suppressed water-level variability in lacustrine settings, means climate-controlled catchment sediment flux may become a dominant allogenic control on mesoscale stratigraphic architecture. However, well-constrained conceptual models and examples of the stratigraphic record of sediment supply variability to deep-water syn-rift lakes are rare due to the paucity of exhumed deep-water syn-rift systems.

The West Xylokastro Fault Block, on the southern margin of the Gulf of Corinth, Greece presents an exhumed Early-Mid Pleistocene deep-lacustrine syn-rift fan system of the Rethi-Dendro Formation. The stratigraphic correlation possible in the West Xylokastro Fault Block permits the tying of stratigraphic architecture recorded in the up-dip Ilias fan-delta, supplying sediment to the deep-water realm, and their stratigraphy and palaeoenvironmental record down-dip. Through combining fieldwork, digital-outcrop investigation with palynological and palaeomagnetic sampling of a behind-outcrop research borehole, a chronostratigraphically-constrained palaeoenvironmental record reveals important changes in sediment supply variability to the deep-water consistent with obliquity-paced oscillations of forest coverage and glacial-interglacial climate variability. Integration of the borehole data, with outcrop observations, highlights that thick, laterally pervasive mudstone intervals can be tied to transgressions of the fan delta, interpreted to be related to sediment supply shutdowns. Sediment supply shutdowns occur during the warming phase of the most severe interglacials of the Early Pleistocene, where the palynological record shows the substantial expansion of warm-temperate, forested vegetation biomes. The role of vegetation in governing sediment supply, through hindering sediment erosion and transport from a catchment, has commonly been linked to reduced sediment yields throughout interglacials. However, the observations in the West Xylokastro stratigraphy highlight that such a model may not appropriate for very severe interglacials where highstand conditions may become highly seasonal, with semi-arid or dry summers, but with very large storms in winters and/or too warm to sustain lowland forests. In these conditions more open, scrubland vegetation permits the erosion and transport of coarse-grained material to the deep-lacustrine fan during the interglacial highstand.

The study informs new conceptual models for climate- and vegetation-controlled sediment supply to deep-water in active margins, which highlight the substantial potential complexity of palaeoenvironmental controls on sediment flux. Binary interglacial vs glacial sediment supply models are likely insufficient for characterising the complexity presented by deep-water syn-rift stratigraphy and highlights a greater need for deep-water stratigraphers to identify suitable proxies (such as palynology) for constraining palaeoenvironmental change.

How to cite: Cullen, T., Collier, R., Gawthorpe, R., Hodgson, D., Maffione, M., Kouli, K., and Kranis, H.: Short, sharp shelves: unravelling palaeoenvironmental controls on sediment supply across active rift-margins to deep-water lakes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2997, https://doi.org/10.5194/egusphere-egu21-2997, 2021.

Soil Organic Carbon (SOC) represents with up to 80% the largest part of the terrestrial’s carbon pool. However, it is still highly debated if soil-carbon is a net atmospheric carbon source or sink. This is mainly due to a paucity of information on the SOC’s fate during soil erosion, which controls the interplay between SOC oxidation during soil storage, transportation, and final storage in a sedimentary sink. The southern hemisphere landmasses have the potential to play a dominant role in the SOC - atmosphere carbon cycle, since wetter (dryer) climates can cause the expansion (contraction) of terrestrial biomass in vast continental areas, such as for example in temperate to semi-arid SE Australia.

We herein investigate the interplay between catchment erosion (quantified by means of uranium isotopes), vegetation density (pollen), the wetland’s response (diatoms), and catchment-wide carbon and nitrogen cycling (carbon and nitrogen isotopes) on glacial/interglacial time scales in SE Australia. The analyses are applied to the sediments of Lake Couridjah, which is part of the Thirlmere Lake system located approximately 100 km SE of Sydney. A previous study has shown that Lake Couridjah and its catchment vegetation are highly sensitive to local and regional climate change. Radiocarbon and luminescence dating revealed that recovered lake sediments cover the time interval between ~140 ka and 100 ka, and between ~17.6 cal yr BP and present day. Lake Couridjah is thus one of the very few sedimentary archives providing a continuous archive for the previous interglacial complex in SE Australia, and thus offers an outstanding opportunity to study SOC cycling in a small catchment across different interglacial boundary conditions. The sedimentary analyses are supported by uranium, carbon, and nitrogen isotope analyses of a soil pit from the vicinity of the lake.

Statistical analyses revealed robust phase-relationships between catchment erosion, vegetation density, and carbon and nitrogen cycling during both glacial-interglacial complexes. The data implies that the density of the catchment’s sclerophyll woodland and mid- to understory vegetation - and not the amount of rainfall - has major control on catchment erosion, and, thus, on SOC storage in the catchment. Overall wetter and warmer peak interglacial conditions promote the expansion of dense sclerophyll vegetation, reducing catchment erosion while simultaneously increasing SOC storage as well as lake productivity and lake carbon-storage. The later post-Eemian phase of the preceding interglacial reveals overall cooler climates and a more open sclerophyll vegetation, resulting in faster catchment-wide erosion and reduced SOC and lake-C storage, conditions that are amplified in glacial periods (post-LGM, penultimate glacial period).

How to cite: Francke, A., Forbes, M., Cadd, H., Short, J. E., Dosseto, A., Tyler, J., Tibbi, J., Marx, S., Dodson, W., and Tim C., C.: Catchment vegetation and erosion controls soil carbon cycling in SE Australia during two Glacial-Interglacial complexes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4100, https://doi.org/10.5194/egusphere-egu21-4100, 2021.

Located at the triple junction of the Pacific, Eurasian and Sunda plates, the island of Sulawesi in Indonesia is one of the most tectonically active places on Earth. This is highlighted by the recurrence of devastating earthquakes such as the 2018 Mw 7.5 earthquake that destroyed the city of Palu and caused several thousand deaths in central Sulawesi. The majority of large magnitude earthquakes on Sulawesi are related to stress release along major strike-slip faults such as the Palu-Koro fault and its southern extensions the Matano and Lawanopo faults. To date, information on the frequency and magnitude of major events on these faults is limited to instrumental records, whereas information from historical sources and natural archives is completely lacking. Considering the increase in population density and its extension into distant areas, it is important to better quantify the seismic hazard. Therefore, a systemic catalogue of past earthquakes is essential for the understanding of tectonic dynamics of the area.

            Lake Towuti, situated in Eastern Sulawesi, is a key site to study the paleoseismology on the island. The lake lies close to the Matano strike-slip fault and is hence an ideal archive for past earthquakes that have occurred in the surrounding area. Moreover, its morphology allows a temporally continuous sedimentary succession. The large and deep central basins of the lake preserve the deposits linked to seismic activity. We combine high-resolution Chirp seismic data with sedimentary analyses of sediment piston cores to assess the recurrence of major earthquakes (Mw > 6) in the area, which are expressed by earthquake-triggered Mass Wasting Deposits (MWD). Five major seismic-stratigraphic units are identified in the upper 200 milliseconds TWT and show different depositional mechanisms. MWD’s and associated seismoturbidites can be easily distinguished in seismic data and are well preserved in the cored sedimentary successions in the topmost Unit 1.1. Chronologically Unit 1.1 covers the last 15 kyrs and enables the establishment of an event chronostratigraphy for Lake Towuti’s recent past. The most recent MWD likely corresponds to an AD 1924 Mw 6.5 earthquake, which was recorded to the south of Lake Towuti. In addition, 11 seismoturbidites have been observed in the Late Glacial to Holocene (~15 kyrs) sediment succession. These results tentatively suggest an average recurrence of major events every 1300 to 1400 years.

How to cite: Tournier, N., Vogel, H., Fabbri, S. C., Anselmetti, F. S., Russell, J. M., Bijaksana, S., and Cahyarini, S. Y.: Seismic event stratigraphy of tectonic Lake Towuti, Sulawesi, Indonesia: a 15 kyrs record of seismo-turbidites, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1048, https://doi.org/10.5194/egusphere-egu21-1048, 2021.

The lake Moo in the northern Apennines, a 0.15 km² basin located at an altitude of 1130 m a.s.l., consists of a small marshy area lying within a portion of a flat semi-circular depression surrounded by steep slopes. The site presents a series of geological and geomorphological characteristics which make it an ideal context to observe the results of flood events on the late Holocene sedimentary record of the basin. Our project aims to establish a relationship between recent deposits, instrumental data and modern-age cartography, in order to obtain site-specific parameters to interpret the sedimentary signal produced by floods on our site. The information can be extended back in time to the millennial scale by analysing sediment cores, in order to observe the frequency and magnitude of flood events throughout the Holocene and assess potential relationships with palaeoclimate reconstructions. This contribution discusses the results from five coring campaigns undertaken between 2018 and 2019 for a total thickness of 10.5 m, which allowed the recording of a c. 500 m long transect stretching from the west slope to the open water on the eastern part of the basin. This extended section enhanced our understanding of the deposit on a larger scale, allowing us to relate the new sequences to the ones identified in previous cores, and develop insights into flood-induced sediment gravity flows and their macroscopic physical characteristics (i.e. grain size, sedimentary structures, Munsell colour and types of contact surfaces). The study has led to the observation of possible correlations between various flood events and Holocene periods.

How to cite: Morandi, L., Segadelli, S., and Cocuccioni, M.: Preliminary sedimentological investigation of a Holocene lake deposit in the northern Apennines (Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7185, https://doi.org/10.5194/egusphere-egu21-7185, 2021.

Sediment records have been widely used to reconstruct Holocene environmental and climate conditions around the world. As new Holocene records from Central America and the Caribbean have become available, new hypotheses have emerged to explain the complex hydroclimate variability in the region. Here we present results from a radiocarbon-dated sediment core recovered from Lake Izabal, eastern Guatemala, that covers the last ~9,500 years. We combined sedimentological, XRF elemental abundances, and principal component (PC) analyses to reconstruct changes in erosion/precipitation, lake productivity, and lake water chemistry during the Holocene. Our results indicate that during the early Holocene, Lake Izabal was a shallow lake with minimal catchment erosion/precipitation as indicated by the abundance of organic-rich mud, coupled with the lowest PC scores and titanium (Ti) abundance of the entire record. An overall increase in the PC scores and a progressive increase in Ti suggest that precipitation/erosion increased from 8,300 to 4,800 cal yr BP and remained high until 1,200 cal yr BP. There was then a significant reduction in erosion and precipitation at ca. 1,200 cal yr BP, as evidenced by a sharp decrease in magnetic susceptibility, terrigenic derived elements, and PC scores. We suggest that the transition towards wetter conditions from the early to the middle Holocene, followed by a stable wet climate until ca. 1,200 cal yr BP, was strongly influenced by a progressive increase in autumn insolation throughout the Holocene, which could have caused an increase in Caribbean sea surface temperatures, increasing moisture availability leading to greater precipitation amounts in the Caribbean coast of Central America.

How to cite: Duarte, E., Obrist-Farner, J., Correa-Metrio, A., and Steinman, B. A.: Holocene climate variability and associated paleoenvironmental changes in the eastern lowlands of Guatemala revealed by a lake sediment from Lake Izabal, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6017, https://doi.org/10.5194/egusphere-egu21-6017, 2021.

High mountain lakes are pristine ecosystems that archive in their sediments high-resolution records of watershed and lake evolution. Understanding how they have responded to Holocene climate fluctuations and anthropic impacts provides essential information to put into a historical context the magnitude and unique features of the current global change.

The REPLIM project funded by the Interreg program (POCTEFA 2014-2020) has implemented a network of lakes in Spain, France and Andorra to study current and past climate, environmental and anthropic changes in lakes. In August 2017, eight short sediment cores were recovered in Montmalús Lake (2433 m a.s.l., Andorra). We present a paleolimnological reconstruction based on sedimentary facies, chemical (main and trace element) analyses and δ¹³C and δ¹⁵N of bulk organic matter. We developed a robust age model based on ²¹⁰Pb, ¹³⁷Cs and ¹⁴C dating for the last 2000 years. Moreover, modern lake dynamics have been characterized with continuous water temperature measurements at various depths, periodical water sampling and sediment traps.

The results show large depositional fluctuations in the lake dynamics, especially during the Little Ice Age, with changes in organic matter accumulation, bioproductivity and sources and increased sediment delivery. Sedimentological and geochemical indicators point to the onset of high human impact in the landscape around the 11^th century. Also, medieval mining and metallurgic activity from 11^th to 14^th centuries increased Pb deposition.

The 20^th century is characterized by a recovery in organic accumulation and bioproductivity rates. Heavy metal deposition also increased during the late 20^th century and started to decrease in the 2010’s decade, without reaching the background values

This study provides the first data on recent changes in lakes from the Principality of Andorra. The results highlight the uniqueness of current global change impacts in alpine lakes and underline the interplay of Great Acceleration and Global Warming processes in these fragile and sensitive depositional systems.

How to cite: Galofré, M.-S., Barreiro, F., Santamaría, I., Copons, R., Komack, B., and Valero, B. L.: How do recent depositional processes changes in high altitude Pyrenean lakes compare with Late Holocene variability? The case of Montmalús Lake (Principality of Andorra, Eastern Pyrenees), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13577, https://doi.org/10.5194/egusphere-egu21-13577, 2021.

High altitude mountain lakes archive high-resolution records of environmental variability (climatic and anthropic). The REPLIM project funded by the INTERREG program (POCTEFA 2014-2020) has implemented a network to understand current and past changes in Pyrenean lakes. In this work, we compare six high altitude lake records along a W- E transect in the South Central Pyrenees: Acherito (1877 m.a.s.l.), La Sierra (2022 m.a.s.l.), Sabocos (1900 m.a.s.l.), Marboré (2600 m.a.s.l), Urdiceto (2364 m.a.s.l.) and Cregueña (2633 m.a.s.l.).

In each lake we have analyzed short sediment cores across transects applying sedimentological (facies, grain size, sediment composition, thin sections), geochemical (XRF scanner, elemental and trace metals) physical (Magnetic Susceptibility), isotopic (δ¹³C and δ ¹⁵N of bulk organic matter) and biological (diatoms) techniques. The age models have been constructed with ¹³⁷Cs, ²¹⁰Pb and ¹⁴C dates.

The sedimentary dynamics and heavy metals depositional history for the last 2000 years provides a temporal context for recent changes. Sedimentary facies variability correlates with climate phases and reflect varied human pressures. In general, during the colder and more humid periods, usually associated with glacier advances (LIA and Late Antiquity LIA), higher surface runoff was generated and, therefore, sediment delivery to the lake increased, in some cases with deposition of coarser facies. Intense watershed disturbances due to human impact were noticeable in lower altitude lakes since early medieval times. All lakes show larger sediment rate variability during the last centuries, but the timing of the onset varies. Lakes located at higher altitudes (Marboré and Cregüeña) show larger changes in sedimentation rates and dynamics around the end of the LIA (ca. 1850 CE), while in lower altitude lakes (Sierra, Sabocos, Acherito) occurred later (ca. 1950 CE).  In most lakes, a significant increase in organic matter accumulation started at the end of the 19th century and the trend accelerated since mid 20th century. Diatom and isotopes analyses suggest an increase in lake primary productivity during the last decades. The results indicate that the combined impacts of climate change and increased human pressure in the Pyrenees at the end of the LIA had a greater impact on high-altitude lakes, but recent changes in the 20th century have affected the lakes at all altitudes

All lakes show a similar heavy metal deposition pattern, with enrichment during Roman and Medieval times and a progressive increase since the end of the 18^th century (industrialization) and reaching its peak in the middle and late 20^th century. Some metals, such as Pb, show a subsequent decline at the end of the 20^th century related to the reduction of industrial emissions and the ban on leaded gasoline.

This integrated approach demonstrates the sensitivity of high altitude lake systems to record past changes and highlights the need for multi-archive studies to support regional reconstructions of past environmental and climate changes.

How to cite: Vicente de Vera García, A., Barreiro Lostres, F., Moreno Caballud, A., Mata Campo, M. P., Corella Aznar, J. P., Pla Rabes, S., and Valero Garcés, B. L.: Sedimentary dynamics and heavy metal deposition in central Pyrenean high altitude lakes during the last 2000 years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15522, https://doi.org/10.5194/egusphere-egu21-15522, 2021.

Tsunamigenic delta collapses in lacustrine environments are still poorly understood phenomena in terms of their recurrence rate, driving mechanism and hazard potential. A partial collapse of the Isola Delta in Lake Sils (Engadine, Switzerland) with an estimated depositional volume of at least 6.5 million m³ is radiocarbon-dated to 548-797 cal CE and may represent a typical tsunamigenic delta collapse in the Alpine environment. Recent studies propose that this basin-wide tsunami with a run-up height of 2–3 m and an inundation distance of 200 m at the lakeshore highlights the importance to better understand these processes and the associated hazards. The collapse was likely triggered by a strong regional earthquake responsible for several simultaneously triggered mass movements in nearby Lake Silvaplana and Lake Como. Increasingly available datasets from Lake Sils (short cores, high-resolution seismic reflection data, numerical tsunami simulations) are now complemented by multibeam swath bathymetry, providing a high-resolution (1 m grid) model of the lake floor that offers new insights into the failed slope masses, and post-failure basin morphology.

Lake Sils is located in the Upper Engadine in southeastern Switzerland at ~1800 m above sea level and has four major sub-basins (Maloja, Central, Sils & Lagrev Basins). A major tectonic element is the Engadine Fault Line (EFL), an oblique sinistral strike-slip fault that runs along the entire Upper Engadine valley. Its influence on the subaqueous morphology of the Maloja Basin in Lake Sils is expressed in the form of several localized troughs and ridges. It is suspected that the fault also cross-cuts the Isola Delta, possibly causing renewed delta failures in case of reactivation. In fact, recent studies have indicated that there is strong evidence for Quaternary left-lateral transcurrent faulting of the EFL, e.g. offsetting a river gully in the Forno Valley close to Lake Sils.

New bathymetric data from Lake Sils and their morphologic interpretations indicate subaquaeous slope failures, the extent of the Isola Delta collapse, and several trough-ridge features within the southwestern Maloja Basin. The latter are possibly indicative of ongoing faulting in the region since such features strongly suggest rhomboidal pull-apart basins within the Maloja Basin along the EFL. In general, such localized troughs within a lacustrine system are expected to level-out over time due to higher sedimentation rates in preferentially deeper regions of the lake. This study thus highlights the use of high-resolution bathymetric data in identifying the combined effects of deep-seated tectonic zones with shallow lake-floor processes, providing new insights into lacustrine hazard studies.

How to cite: Fabbri, S. C., Nigg, V., Bellwald, B., Kremer, K., and Anselmetti, F. S.: Neotectonic activity in Lake Sils (Engadine, Switzerland) as trigger of tsunamigenic delta collapses?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15839, https://doi.org/10.5194/egusphere-egu21-15839, 2021.

Shallow and closed lakes are affected by meteorological and climate variations and are especially sensitive to the change in their hydrological balance. In central Italy, there is the fourth-largest lake of the country, the Trasimeno Lake, whose water level has undergone various fluctuations over the centuries with alternation of flood and drought periods because of its shallow depth and the absence of natural outflows [1].

Sediment archives are used as information records to study chemical, physical, and biological environmental variations and changes in the hydrological budget driven by climatic fluctuations, but this is particularly complicated in shallow lakes due to the multiple perturbative phenomena. A robust study depends on the ability to obtain valid high-resolution geochemical data from lake sediments.

We conducted high-resolution geochemical analysis on three sediment cores about 1 meter long each, collected in Lake Trasimeno. We sectioned at 1  or 2 cm interval, which provided a detailed characterization of the significant changes in lacustrine processes that occurred in the basin during the Anthropocene (~last 150 years) [2], combining quantitative chemical (ICP-OES) and semi-quantitative (XRD and SEM) investigations. Geochemical variables are used as paleolimnological proxies to reconstruct past lake events that occurred within the water column. In particular, we report the study of the endogenic precipitates characteristic of the Trasimeno sediments, whose precipitation processes have been influenced by water fluctuations and anthropogenic impacts.

Given the strong presence of water fluctuations, the investigation period was divided into three distinct phases related to the lake's hydrometric state and characterized by sedimentary compounds of different nature. The endogenic carbonate compounds of calcite (commonly present in the Trasimeno sediments) contain a different Mg percentage during the different hydrometric phases. The lake sediments are particularly rich in Mg-calcite due to both water level changes and biological effects. Moreover, co-precipitation of non-crystalline Ca-P compounds (e.g., apatite type) has been detected during a hydrometric phase characterized by high microorganisms activity. Precipitation processes were triggered in Trasimeno by the growth of nutrient discharge into the lake (since the 1970s) and are currently studied for their importance in controlling eutrophication phenomena.

In conclusion, our findings show that rapid lake responses to water fluctuations and climate variations were transcribed within the sedimentary stratigraphic archives, which underlines their value and high quality in paleoenvironmental and paleohydrological reconstruction.

References:

[1] Frondini, Dragoni, Morgantini, Donnini, Cardellini, Caliro, Melillo, and Chiodini (2019). An En-dorheic Lake in a Changing Climate: Geochemical Investigations at Lake Trasimeno (Italy).Water, 11(7):1319.

 [2] Gaino, E., Scoccia, F., Piersanti, S., Rebora, M., Bellucci, L. G., and Ludovisi, A. (2012). Spiculerecords of Ephydatia fluviatilis as a proxy for hydrological and environmental changes inthe shallow Lake Trasimeno (Umbria, Italy). Hydrobiologia, 679(1):139–153.

How to cite: Gravina, P., Moroni, B., Vivani, R., Ludovisi, A., Selvaggi, R., and Cappelletti, D.: Stratigraphy and sedimentary process in a closed-basin lake in Central Italy during the Anthropocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7468, https://doi.org/10.5194/egusphere-egu21-7468, 2021.

Located between the temperate and arid climates of Europe and North Africa, Iberia is one of the most climatic vulnerable regions of Europe with more severe and longstanding extreme climate events being expected in this region. The Iberian climate, mainly in winter, is modulated by the North Atlantic Oscillation (NAO). Persistent positive (negative) NAO phases, can lead to significant changes in the North Atlantic westerly wind-belts, resulting in strengthened (weakened) winter precipitation in Western Iberia.

The Iberian Central System mountain range constitutes one of the biggest physical barriers to the moist air masses coming from the Atlantic Ocean. Usually, under low anthropic influence, the high mountain lake ecosystems have sensitive responses to climate and environmental changes, which makes lake sediments a pristine record for paleo reconstructions.

The increasing number of studies on Iberian high lakes depicted a wide spectrum of spatiotemporal variability in climate and environmental conditions for the last few millennia. However, the paucity of archives from the western region hampers the understanding of the effect of major climate forcings on different climate periods.

In this sense, to assess the past hydroclimatic patterns over western Iberia, we study upper 120 cm sediments of a 5 m core retrieved from a high mountain lake in central Portugal (Lake Peixão, Serra da Estrela). The age and depth model provides a robust chronology of the last 3600 years based on four ¹⁴C AMS dating on pollen concentrates and ¹³⁷Cs and ²¹⁰Pb profiles.

Here we present the preliminary results on sedimentary lipid biomarker (leaf wax n-alkane) and compound-specific hydrogen isotope (δD_wax) analysis performed at centennial time scale resolution. n-Alkane characterization, based on diverse indices (e.g., ACL, CPI, Paq, relative percentages, etc.), shows a clear higher plant signal, with a strong odd-over-even carbon predominance of long-chain n-alkanes, and predominance of the C₃₁ homologue. Principal component analysis (PCA) applied to the odd n-alkanes (C₁₇ – C₃₅) concentrations reduced the data dimensionality into two principal components (PC). The PC1 mostly represents total n-alkane concentrations. PC2 has a positive correlation with Paq, C₂₇, and δD signals, while a high negative correlation with ACL. Another important feature of the PC2 signal is its parallelism with NAO index reconstructions.

Our new data show a sensitive response from the lake catchment vegetation to hydroclimatic variability and allow the reconstruction of climatic phases occurring in this region based on plant waxes from Lake Peixão.

Acknowledgments

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: N. Santos, R., Rodrigues, T., Schefuß, E., Naughton, F., Oliveira, D., Ramos, A., and Hernández, A.: Hydroclimate reconstruction of Western Iberia over the last 3600 years - insights from lipid biomarker and specific isotope signal, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8820, https://doi.org/10.5194/egusphere-egu21-8820, 2021.

Lake sediments bear valuable information allowing multidisciplinary research to address paleoclimatic and paleoenvironmental reconstructions at regional to global scales. Sedimentological, geochemical, paleontological and biological tools are commonly used to tackle these questions, which are generally driven by a set of intricated parameters. Among them, the importance of biogeochemical cycling is largely acknowledged in the lake (paleo-) water columns and has been at the heart of most paleolimnological studies. The way these signals are transferred to lake sediments has largely been studied. However, microbial communities - the principal actors in the biogeochemical cycling framework - keep being active in the sediment, and continue to influence the preservation and retention of organic and inorganic matter while buried. Gathered within the “early diagenesis” black box, these processes, once qualified, can help better interpret the proxies they may influence, and even constitute new ones. Within this work, we provide examples showing that the integration of studies of the subsurface biosphere within geo- and paleo-limnology investigations can help unlock or secure the potential of multiproxy analysis for reconstructing the paleoenvironments, paleoclimates and paleo-ecology of lake basins. The use of now well-developed OMICS methods, through the analysis of environmental and/or ancient DNA and lipids in particular has been coupled to mineralogical, isotopic and magnetic information in the Dead Sea (Levant) to demonstrate the differential preservation of mineralogic and sedimentologic signals along the last two glacial-interglacial cycles (Thomas et al., 2015, 2016; Ebert et al., 2018). Similar signals have been unlocked in Lake Towuti (Indonesia) and in Laguna Potrok Aike (Argentina) (Vuillemin et al., 2015, 2017). In Lake Ohrid (North Macedonia/Albania), environmental DNA has provided limited inputs on that perspective (Thomas et al., 2020), but has shown that ancient/fossil DNA could provide valuable information regarding the lake primary productivity and the status of its watershed land-cover. Integrating OMICS methods to tackle the identity and activity of the ancient and modern subsurface biosphere of lakes therefore holds an immense potential not only for microbiology investigations, but also for paleoclimatic and paleoenvironmental reconstructions.

Ebert et al. (2018) Overwriting of sedimentary magnetism by bacterially mediated mineral alteration. Geology 46, 2–5.

Thomas et al. (2016) Microbial sedimentary imprint on the deep Dead Sea sediment. The Depositional Record 1–21.

Thomas et al. (2020) Weak influence of paleoenvironmental conditions on the subsurface biosphere of lake ohrid over the last 515 ka. Microorganisms 8, 1–20.

Thomas et al. (2015) Impact of paleoclimate on the distribution of microbial communities in the subsurface sediment of the Dead Sea. Geobiology 13, 546–561.

Vuillemin et al. (2015) Recording of climate and diagenesis through fossil pigments and sedimentary DNA at Laguna Potrok Aike, Argentina. Biogeosciences Discussions 12, 18345–18388.

Vuillemin et al. (2017) Preservation and Significance of Extracellular DNA in Ferruginous Sediments from Lake Towuti , Indonesia. Frontiers in Microbiology 8, 1–15.

How to cite: Thomas, C., Vogel, H., and Ariztegui, D.: Unlocking the power of lake multiproxy analyses by understanding subsurface biosphere processes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8379, https://doi.org/10.5194/egusphere-egu21-8379, 2021.