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Ancient iron formations hold important records of environmental conditions during the Precambrian eons. Reconstructions of past oceanic systems require investigation of modern ferruginous analogs to disentangle water column and diagenetic signals recorded in iron-bearing minerals. We analyzed oxygen, iron, and carbon isotopes in siderite, a ferrous carbonate phase commonly used as an environmental proxy, from a 100-m-long record spanning a 1 Ma depositional history in ferruginous Lake Towuti, Indonesia. Combining bulk sediment and pore water geochemistry, we traced processes controlling siderite isotope signatures. We show that siderite oxygen isotope compositions (δ18O) reflect in-lake hydrological and depositional conditions. Low iron isotope values (δ56Fe) record water column oxygenation events over geological timescales, with minor diagenetic partitioning of Fe isotopes by microbial iron reduction after deposition. The carbon isotope compositions (δ13C) reflect the incorporation of biogenic HCO3–, which is consistent with sediment organic matter remineralization lasting over ca. 200 ka after burial. Positive δ13C excursions indicate an increased production of biogenic methane that escaped the sediment during low lake levels. Diffusion across the sediment–water interface during initial formation of siderites tends to align the isotope signatures of bottom waters to those of pore waters. As microbial reduction of ferric iron and oxidation of organic matter proceed and saturate pore water conditions with respect to siderite, overgrowth on nuclei partially mutes the environmental signal inherited from past bottom waters over ca. 1 Ma. Because high depositional fluxes of ferric iron and organic matter in early oceans would have promoted similar microbial processes in ferruginous deposits prior to lithification, the environmental record contained in siderite grains can successively integrate depositional and early diagenetic signals over short geological timescales.

Abundant evidence from marine, ice-core and terrestrial records demonstrates that Earth’s climate has experienced co-evolution of orbital- and millennial-scale variability through the Pleistocene. The varying magnitude of millennial climate variability (MCV) was linked to orbitally paced glacial cycles over the past 800 kyr. Before this interval, global glaciations were less pronounced but more frequent, yet scarcity of a long-term integration of high-resolution continental and marine records hampers our understanding of the evolution and dynamics of MCV before the mid-Pleistocene transition. Here we present a synthesis of four centennial-resolved elemental time series, which we interpret as proxies for MCV, from North Atlantic, Iberian margin, Balkan Peninsula (Lake Ohrid) and Chinese Loess Plateau. The proxy records reveal that MCV was pervasive and persistent over the mid-latitude Northern Hemisphere during the past 1.5 Myr. Our results suggest that the magnitude of MCV is not only strongly modulated by glacial boundary conditions on Earth after the mid-Pleistocene transition, but also persistently influenced by variations in precession and obliquity through the Pleistocene. The combination of these four proxies into a new MCV stack offers a credible reference for further assessing the dynamical interactions between orbital and millennial climate variability. Orbital forcing consistently influenced the magnitude of millennial-scale climate variability through the Pleistocene, according to an analysis of four high-resolution Northern Hemisphere proxy records covering the past 1.5 Myr.

High-mountain lake records in semiarid foreland settings, such as the central Andes of North-western Argentina, are highly restricted and often deprived of well-preserved microstratigraphic information to analyze palaeoenvironmental changes and their causes, particularly for periods prior to the Last Glacial Maximum. Laguna La Salada Grande (23°S/65°W, 4063 metres above sea-level) is a closed shallow lake located at Cordillera Oriental, North-western Argentina with a unique depositional record, including geomorphic and stratigraphic evidence of palaeoenvironmental changes since the Late Pleistocene. In order to understand the depositional dynamics of this mountain lacustrine system at different timescales, limnogeological multiproxy analyses together with a radiocarbon and 210Pb-based chronology were applied on massive and laminated sediments from La Salada Grande. Laminated deposits were further analyzed using novel sub-centimetric mineralogical, textural and geochemical automated methods (including a combination of micro-X-ray fluorescence and quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN®). Thick laminated microfacies at the beginning of the sequence record a deep and organic matter productive palaeolake prior to ca 34 ka (1 ka = 1000 years before 1950), that changed into a highly fluctuating shallower-palaeolake with frequent detrital influxes after ca 34 ka. Microstratigraphy of the coarser-grained detrital laminae between 31 ka and 25 ka reveals irregular and probably sub-centennial high-energy discharge events, pointing to convective atmospheric activity as the main trigger. After ca 21 ka the lake evolved to deeper water-level conditions resulting in fine-grained deposits with limited delivery of coarse-grained sediments, followed by an abrupt lake level drop and incision. The multi-millennial palaeoenvironmental reconstruction of La Salada Grande, and its correlation with other palaeoclimate records, shows a close link between the lacustrine depositional processes and palaeoclimate changes associated with the South American summer monsoon dynamics. This multifocal research in such an understudied environment provides key knowledge about lacustrine functioning and discharge events−climate interactions of mountain lakes of semi-arid climates., Sedimentology, 69 (6), ISSN:0037-0746, ISSN:1365-3091

Continental and marine sediments are composed of a mixture from different sources and are influenced by a variety of environmental factors and transport processes prior to deposition. For analysis and interpretation, these sources and processes are often challenging to disentangle. We show that end-member modelling of X-ray fluorescence (XRF) core-scanning data helps to overcome these challenges by unmixing different environmental signals from high-resolution sediment geochemical records. We apply this approach to a 100 m long lacustrine succession from Lake Towuti, Indonesia, to separate the regional climate and tectonic history from local ecological and diagenetic processes. The resulting six end-members (EMs) are interpreted to represent changes in ecological (EM1), climatic (EMs 2–4), tectonic (EM 5) and geomorphic (EM6) processes determining changes in sediment composition. Because end-member analysis allows for the tracking of transient and overlapping processes, climatic changes can be followed throughout the 100 m-long succession, suggesting alternating wet and dry periods in Central Sulawesi over long (several 100 000 years) time scales. We show that end-member analysis on elemental data sets offers a detailed and objective means to disentangle depositional processes in sedimentary successions resulting from varying tectonic and environmental factors involved in sediment formation and deposition.

The Weihe Basin, enclosed by the Chinese Loess Plateau to the north and the Qinling Mountains to the south, is an outstanding, world-class continental site for obtaining high-resolution multi-proxy records that reflect environmental changes spanning most of the Cenozoic. Previous geophysical and sedimentary studies indicate that the basin hosts 6000–8000 m thick fluvial–lacustrine sedimentary successions spanning the Eocene to Holocene. This sedimentary record provides an excellent and unique archive to decipher long-term tectonic–climate interactions related to the uplift of the Tibetan Plateau, the onset/evolution of the Asian monsoon, and the development of the biogeography of East Asia. Owing to its location at the interface of the opposing westerly and Asian monsoon circulation systems, the Weihe Basin also holds enormous promise for providing a record of changes in these circulation systems in response to very different boundary conditions since the Eocene. To develop an international scientific drilling programme in the Weihe Basin, the Institute of Earth Environment, Chinese Academy of Sciences, organized a dedicated workshop with 55 participants from eight countries. The workshop was held in Xi'an, China, from 15 to 18 October 2019. Workshop participants conceived the key scientific objectives of the envisaged Weihe Basin Drilling Project (WBDP) and discussed technical and logistical aspects as well as the scope of the scientific collaboration in preparation for a full drilling proposal for submission to the International Continental Scientific Drilling Program (ICDP). Workshop participants mutually agreed to design a two-phase scientific drilling programme that will in a first phase target the upper 3000 m and in a second phase the entire up to 7500 m thick sedimentary infill of the basin. For the purpose of the 7500 m deep borehole, the world's only drill rig for ultra-deep scientific drilling on land, Crust 1, which previously recovered the entire continental Cretaceous sediments in the Songliao Basin, will be deployed in the WBDP.

Chromium stable isotope composition (δ

The introduction of vertical mobility for agro-pastoral activities marks an important change in prehistoric society, which has altered the socioeconomic structuring of Alpine areas. It has also had severe consequences for the high Alpine ecosystems, including the destabilisation of soils, sustained vegetation disturbance, and lake eutrophication. With climate change and increasing anthropogenic pressure to Alpine environments, it is critical to better characterise the interaction between natural and anthropogenic factors that have shaped Alpine environments during the last millennia.We present a Holocene record of domestic and wild animal presence through sediment-DNA analysis from a lake sediment core from the Eastern Swiss Alps and study the effects on soil erosion and vegetation composition. We provide direct evidence for the onset of pastoralism around 5,000 years BP, after which the site became repeatedly abandoned and re-occupied. According to our sediment-DNA reconstructions, several domestic species are present during early occupational periods, while cattle herding has become dominant during the last millennium. The latter period also coincides with a severe change in vegetation composition. Pastoral activities have had marked effects on soil erosion, while catchment deforestation already occurred ~2,000 years prior to the first findings of DNA from domestic animals, suggesting that the onset of Alpine pastoralism did not cause severe vegetation changes in our catchment. Further, sediment-DNA findings indicate that wild animals avoided near-shore territories during periods of human occupation, but returned to the lake shore upon site abandonment.Our study opens a new perspective on long-term human-environment interactions in Alpine environments by providing direct evidence for animal presence and diversity and linking this information to physical and ecological factors such as soil erosion and vegetation change.

Lake Cadagno, a meromictic, redox stratified lake located in Val Piora in Switzerland has extensively been studied serving as a modern analogue of the Archean/Proterozoic ocean. Euxinic conditions were established after a short transition interval immediately following lake formation ~10’000 years ago. Overall elevated but very variable Mn concentration during this transition period have been thought to reflect fluctuating bottom water redox condition with authigenic accumulation of sedimentary Mn from the water column in line with observation from deep basins of the Baltic Sea.To test this hypothesis we measured the Mo isotopic composition of Lake Cadagno sediments with a focus on the transition interval following lake formation between 7.4 and 7.8 m depth. With a δ98/95MoNIST+0.25 composition ranging from -1.72 to +3.77‰ the Mo isotopic variability of the transition interval sediments is significantly larger compared to Cadagno sapropels deposited under euxinic conditions and significant larger compared to the entire Mo isotopic variability observed in marine reservoirs. Aside this large variability in δ98/95MoNIST+0.25 a gradual change from isotopically very light to very heavy Mo isotopic composition upcore is observed. This transient sedimentary Mo isotope pattern cannot be explained by fluctuating bottom water redox conditions at the beginning of the lake and cannot be a primary signature caused by changes in the depositional environment. Likely, the inflow of oxic groundwater from subsurface karst aquifers present in Cadagno into organic-matter-rich lake sediments, a likely active and currently ongoing process, causes the formation of a chemocline at depth in the sediment column. Here the reduction of sulphate and the precipitation of isotopically light Mo from the dissolved oxic groundwater reservoir causes progressively higher δ98/95MoNIST+0.25 upwards in the sediment column.

The East African (hydro-)climate response to perturbations during the deglacial transition (e.g. Older and Younger Dryas) is complex and expressed heterogeneously in different paleoclimatic records. Lake Victoria (LV), Africa’s largest lake, desiccated entirely during the dry last glacial (>16.3 kyr BP) and subsequently refilled as climate conditions got more humid, reaching a highstand during the Early Holocene. However, existing sediment records from LV do not have sufficient resolution to fully resolve short-term hydroclimate changes during the deglacial transition (especially between 14 and 11 kyr BP). There is little direct evidence of late-glacial lake level fluctuations in LV so far because intermediate water depth coring sites suitable to record intermittent lowstands are missing.By analysing sediment cores along a near-shore/shallow water (current water depth 22 m) to offshore/deep water (current water depth 63 m) coring transect covering the past 16,000 years, we aim at a more accurate spatial and temporal reconstruction of LV’s deglacial lake level history in response to regional hydroclimate changes.Core stratigraphy and geochemical evidence, combined with a robust radiocarbon chronology, demonstrate a stepwise infilling of the Lake Victoria basin after its last complete desiccation (< 16.3 kyr BP). Following the dry late glacial Heinrich 1 event, an intermediate water level prevailed between 16.3 and 14.4 kyr BP, with uninterrupted deposition of fine-grained, organic matter-rich pelagic muds at our deep-water site and coarser, sandy-clay deposits at the near shore site. A second dry episode during the Older Dryas (~14 kyr BP) is marked by an abrupt decline in lake level with deposition of coarse mollusc shell bearing sediments at the near shore site indicating a littoral depositional environment. This shift in hydroclimate in the Lake Victoria basin is congruent with a brief period of cooling and drying during the Bölling/Alleröd (Dansgard Oeschger Event 1), which is also recorded in other East African Lakes. Subsequently, Lake Victoria reached maximum water levels with the onset of the African Humid Period in the early Holocene at around 11 kyr BP, which is expressed by elevated input of chemically weathered material (e.g. Rb/K) and deposition of fine-grained muds at both the near shore and offshore sites.

Carbohydrates are a ubiquitous constituent of living organisms and an important contributor to global sedimentary carbon pools. Yet, the factors that control the pool size and degradation of sedimentary carbohydrates are not well understood. Here, we investigated carbohydrate cycling over a complete Holocene sedimentary succession in high-altitude, meromictic Lake Cadagno (Switzerland). This succession includes sedimentary records of a stepwise evolving lake redox history from oxic, hypoxic to euxinic anoxic, as well as intercalated layers of lacustrine and event deposits. Event deposits differ from lacustrine layers in organic carbon content, stable isotope signatures, carbohydrate contents, and carbohydrate macromolecular compositions (pyrolysis gas/mass spectrometry) indicating significant terrestrial inputs. However, past changes in redox conditions, implied by redox-sensitive elements (e.g. Mn, Fe, Mo, and S), are not reflected in carbon isotope and carbohydrate data. Carbohydrate contributions are stable, or even increase, with sediment age and show compound-specific variations. Certain carbohydrate pyrolysis products of likely aquatic origin, such as levoglucosan, increase in percentage with sediment age, whereas others, such as furaldehyde, decrease with age. On the other hand, pyrolysis products that are of likely terrestrial origin, such as 3-acetamido-methylfuran, decrease strongly with age. In contrast to carbohydrate macromolecules, gas chromatography with flame-ionization detection analyses showed no clear changes in total hydrolyzed carbohydrate monomer compositions in relation to sediment age or between aquatic- and terrestrial-dominated layers. Our results indicate that carbohydrate degradation in sediments is mainly controlled at the macromolecular level. Notably, our findings suggest that carbohydrates can be well-preserved over the entire Holocene in lake sediments and that aquatic carbohydrates are in some cases selectively preserved over their terrestrial counterparts in these sediments.

Recently, non-traditional stable isotope systems have become new tools to track weathering and sediment transport processes and to obtain information about the lithological and chemical composition of drainage networks. Because the Ti isotope composition (δ49Ti) increases with the SiO2 concentration of rocks, Ti isotopes have received increasing attention to reconstruct the chemical composition of the continental crust through time (Greber et al., 2017). Chemical weathering and hydrodynamic sorting of sediments during transport may however cause fractionation of Ti isotopes and bias the δ49Ti of the sediment record (Klaver et al., 2021; Xinyue et al., 2022).To investigate potential biases and their extent in the sedimentary record, we measured the δ49Ti signature of lacustrine sediments and respective catchment bedrock and weathering profiles from two study areas that represent geochemical and weathering endmembers; (i) Lake Grimsel in Switzerland displaying a felsic catchment dominated by physical weathering and (ii) Lake Towuti in equatorial Sulawesi, Indonesia, with an ultramafic to mafic catchment and intense chemical weathering.Shallow sediments collected at Lake Grimsel composed of different particle sizes ranging from clay to gravel, as well as samples from a sediment core spanning the past 10 kyr, display a constant δ49/47Tiof +0.32 ± 0.03‰. This value is expected from the granodioritic protolith in the catchment. We also did not find any Ti isotope fractionation associated with chemical weathering based on two soil profiles from the catchment of Lake Towuti in Indonesia. Furthermore, samples from a sediment core from Lake Towuti spanning the past ~1 Myr display δ49Tiin a narrow rangebetween +0.09 to +0.17 ‰ (both ± 0.03‰; 2SD), and this value is between the Ti isotope signature present in soil and bedrock in the catchment that range from +0.07 to +0.26‰ (both ± 0.03‰; 2SD). Due to the heterogeneous δ49Ti of the catchment of Lake Towuti further mass balance modeling is required to assess if the Ti isotopic composition of the lake sediments reflects that of the eroded protolith. REFERENCESGreber, N. D., Dauphas, N., Bekker, A., Ptáček, M. P., Bindeman, I. N., & Hofmann, A. (2017). Titanium isotopic evidence for felsic crust and plate tectonics 3.5 billion years ago. Science, 357(6357), 1271-1274.Klaver, M., MacLennan, S. A., Ibañez-Mejia, M., Tissot, F. L., Vroon, P. Z., & Millet, M.-A. (2021). Reliability of detrital marine sediments as proxy for continental crust composition: The effects of hydrodynamic sorting on Ti and Zr isotope systematics. Geochimica et Cosmochimica Acta.Xinyue, H., Jinlong, M., Gangjian, W., Zhibing, W., Le, Z., Ti, Z., & Zhuoying, Z. (2022). Mass-dependent fractionation of titanium stable isotopes during intensive weathering of basalts. Earth and Planetary Science Letters, Volume 579.

Variation in molybdenum (Mo) concentration and isotope composition is an established tracer for redox changes in marine environments. Here we apply Mo as a proxy of past water column oxygenation in ancient ferruginous and hyposulfidic Lake Towuti. Lake Towuti is >1.2 Myrs old, up to 200m deep, weakly stratified and anoxic below ~100 m water depth, and surrounded by an ultramafic bedrock-dominated catchment in South Sulawesi, Indonesia. Despite the current permanent stratification, deeper water mixing and oxygenation occurred periodically in the past due to Towuti’s sensitivity to climate change. To better reconstruct the redox changes through time, we present Mo concentration and isotope data from laterite profiles overlying ultramafic bedrock, lake surface sediments, and a ~30 kyr sediment piston core from Lake Towuti, Indonesia.Although Mo concentrations in laterite profiles are overall higher compared to the underlying bedrock, the absence of a significant Mo isotopic variability with values close to the unweathered ultramafic protolith, varying from –0.16‰ to –0.04‰ δ98MoNIST3134, suggests low aqueous mobility of Mo during weathering due to the formation of laterite Fe-oxides. In contrast to the laterite samples, Mo isotopic variability in lake surface sediments show a larger variability varying from –1.15‰ to –0.13‰ δ98MoNIST3134 with a significantly lighter Mo isotopic composition in sediments deposited under oxic bottom water conditions. This light Mo isotopic composition is likely caused by early diagenetic redox cycling of Mo and Fe at the sediment-water interface. In the deeper, anoxic parts of the basin, Mo isotopic compositions show values close to the laterite input with elevated sedimentary Mo concentrations which are likely the result of an authigenic Mo enrichment from the water column. Mo isotope variability in sediments taken from a piston core in the deep part of the lake is in the range of Mo isotope compositions from modern surface sediments, varying from –0.14‰ to –0.66‰ δ98MoNIST3134. Interestingly, this variability is well correlated with local and global indicators of climate change from previous studies. Sediments deposited between ~30 kyr and ~10 kyr exhibit Mo isotope signatures similar to present-day oxygenated shallow water sites, thereby suggesting enhanced lake mixing and bottom water oxygenation under drier and colder climate conditions of the last glacial period. Sediments deposited since ~10 kyr under wetter and warmer climate conditions exhibit Mo isotope signatures similar to present-day anoxic deeper water settings. These suggest that Mo isotope compositions of lake sediments are potential quantitative indicators of past climate-driven water column oxygenation.

The modern, over 250-m-deep basin of Lake Constance represents the underfilled northern part of an over 400-m-deep, glacially overdeepened trough, which reaches well into the Alps at its southern end. The overdeepening was formed by repeated glacial advance-retreat cycles of the Rhine Glacier throughout the Middle to Late Pleistocene. A seismic survey of Lake Constance revealed a Quaternary sediment fill of more than 150 m thickness representing at least the last glacial cycle. The stratified sedimentary fill consists at the base of ice-contact deposits on top of the molasse bedrock, overlain by glaciolacustrine to lacustrine sediments. During the successful field test of a newly developed, mid-size coring system ("HIPERCORIG"), the longest core (HIBO19) ever taken in Lake Constance was retrieved with an overall length of 24 m. The sediments recovered consist of a nearly continuous succession of lacustrine silts and sands including more than 12 m of Late Glacial sediment at the base. 14 lithotypes were identified through petrophysical and geochemical analyses. In combination with a 14C- and OSL-based age-depth model, the core was divided into three main chronostratigraphic units. The basal age of ~13.7 ka BP dates the base of the succession back to the Bølling-Allerød interstadial, with overlying strata representing a complete and thick Younger-Dryas to Holocene succession. The sediments offer a high-resolution insight into the evolution of paleo-Lake Constance from a cold, postglacial to a more productive, warm Holocene lake. The Late Glacial succession is dominated by massive, m-thick sand beds reflecting episodic sedimentation pulses. They are most likely linked to a subaquatic channel system originating in the river Seefelder Aach, which is, despite the Holocene drape, still apparent in today's lake bathymetry. The overlying Holocene succession reveals a prominent, several cm-thick, double-turbiditic event layer representing the most distal impact of the Flimser Bergsturz, the largest known rockslide of the Alps that occurred over 100 km upstream the river Rhine at ~9.5 ka BP. Furthermore, lithologic variations in the Holocene succession document the varying sediment loads of the river Rhine and the endogenic production representing a multitude of environmental changes.

The pH is a fundamental determinant for physico-chemical reactions in aquatic environments but notoriously difficult to reconstruct in paleo records. Experimental studies have shown that the δ66Zn isotopic composition of calcite is strongly pH dependent in the 7.0 ≤ pH ≤ 8.0 range, with lower δ66Zn at higher pH, making it a suitable pH proxy in settings with endogenic calcite precipitation (Mavromatis et al. 2019). Here we applied the calcite δ66Zn pH proxy to a sediment core covering the recent anthropogenic eutrophication at Lake Greifen, Switzerland to test its applicability in a natural setting that has undergone a productivity-driven shift in surface water pH. Lake Greifen is a hard water lake with a surface water pH ranging between >8.5 during spring and summer algal blooms and ~7.5 in the remainder of the year. Sediments deposited in the center of the lake are predominantly composed of endogenic calcite (>75 %wt) with the remainder comprising varying amounts of organic matter and biogenic silica and only minor detrital matter. Pure calcite samples for this study were collected from sediments deposited during both the oligotrophic and eutrophic lake phases to capture a wide range in pH. Lake Greifen sedimentary calcite δ66Zn values relative to the JMC3-0749L standard range between 0.71 ± 0.05 ‰ in sediments deposited under oligotrophic conditions to 0.29 ± 0.01 ‰ in sediments deposited under eutrophic conditions. Lower δ66Zn values during the more recent eutrophic lake phase may thus be explained by a productivity-driven change in surface water pH. Interestingly, δ66Zn values around 0.3 ‰ have been reported for calcite precipitating at pH >8 in experimental studies, which is very close to Lake Greifen’s modern surface water pH recorded during spring and summer algal blooms. δ66Zn values around 0.7 ‰, reported in samples originating from the less productive oligotrophic phase of Lake Greifen, are indicative for a pH 66Zn water isotope compositions are required to further confirm our findings but the preliminary results of this study suggest δ66Zncalcite to be a promising pH proxy candidate in paleo records. ReferenceMavromatis, V.; Gonzalez, A.G.; Dietzel, M.; Schott, J. (2019) Zinc isotope fractionation during the inorganic precipitation of calcite – Towards a new pH proxy. Geochimica et Cosmochimica Acta 244, 99 – 112.

Anthropogenic eutrophication and spreading anoxia in freshwater systems is a global concern. Little is known about anoxia in earlier historic times under weaker human impact, or under prehistoric natural conditions with different trophic, land cover and climatic regimes. We use a novel approach that combines high‐resolution hyperspectral imaging with μ‐XRF and HPLC‐pigment data, which allows us to assess chloropigments (productivity) and bacteriopigments (anoxia) at seasonal subvarve‐scale resolution. Our ~9700 cal a BP varved sediment record from NE Poland suggests that productivity increased stepwise from oligotrophic Early Holocene conditions (until ~9200 cal a BP) to mesotrophic conditions in the Mid‐ and Late Holocene. Natural eutrophication was mainly a function of progressing landscape evolution with intense weathering under dense forest and warm‐moist climatic conditions. Generally, anoxia increased with increasing productivity. Seasonal anoxia and some multi‐decadal periods of meromixis were the common mixing patterns throughout the Holocene except for a period of persisting meromixis between ~5200 and 2000 cal a BP. Anthropogenic deforestation around 400 cal a BP resulted in substantially better lake oxygenation despite high productivity. In this small lake, aquatic productivity and lakeshore forest cover (wind shield) were more important factors controlling oxic/anoxic conditions than Holocene temperature variability.

The Quaternary is characterized by a series of glacial-interglacial cycles and a shift in the Earth's climate state known as the mid-Pleistocene Transition (MPT, ca. 1200 ka to 720 ka). The progressive increase in glacial cycle length from approximately 41 ka to on average 100 ka affected marine and terrestrial life, but how it affected freshwater communities is far less known. Here, diatom and paleoenvironmental data between 1050 ka and 815 ka from a sediment succession of ancient Lake Ohrid are used to understand how the freshwater communities responded to environmental changes during key-periods of glacial intensification associated with the MPT. Based on stratigraphically constrained incremental sum of squares cluster (CONISS), a distinct diatom community turnover in Lake Ohrid was identified during the study period. The first community existed between 1050 and 955 ka MIS (Marine Isotope Stages) 30–25 and was mostly influenced by environmental parameters related to nutrient supply, mixing processes and primary productivity in the lake. The second community existed between 955 and 815 ka (MIS 25–21) and was largely driven by ontogenetic processes related to the ongoing deepening of the lake, changes in bottom water redox conditions and changes in mixing processes in the lake. The increased severity and duration of cold, glacial stages during the MPT shows only a weak impact on the diatom community in Lake Ohrid. Shifts in species phenotypes, abundance and composition are found in both communities, likely as adaptation in response to the changing environmental conditions. This study shows that the diatom communities were only weakly affected by the progressive intensification of the glacial intensity during the MPT, emphasizing the role of local environmental changes in regulating freshwater communities.

This study provides a detailed reconstruction of cold-water coral mound build-up within the East Melilla Coral Province (southeastern Alboran Sea), more precisely at the northern part of Brittlestar Ridge I, over the last 300 kyr. The multiproxy investigation of core MD13-3462G reveals that mound build-up took place during both interglacial and glacial periods at average aggradation rates ranging between 1 and 10 cm kyr(-1). These observations imply that corals never thrived but rather developed under stressful environmental conditions. Maximum aggradation rates of 18 cm kyr(-1) are recorded during the last glacial period, hence providing the first evidence of coral mound development during this time period in the western Mediterranean. The planktonic (Globigerina bulloides) and benthic (Lobatula lobatula) delta O-18 records from core MD13-3462G show typical interglacial-glacial variations during the last two interglacial-glacial cycles. This is in contrast with delta O-18 records generally recovered from coral mounds and highlights that the northern part of Brittlestar Ridge I experienced reduced albeit relatively continuous accretion. High abundances of infaunal benthic foraminifera (Bulimina marginata, Bulimina striata, and Uvigerina mediterranea) suggest that weak seafloor oxygenation associated with important terrestrial organic matter input characterized interglacial periods, whilst the dominance of large epibenthic species (Discanomalina coronata and Lobatula lobatula) and Miliolids is probably linked to stronger Levantine Intermediate Water circulation and fresher organic matter input during glacial periods. In addition, the computed tomography (CT) quantification of macrofaunal remains shows that the bryozoan Buskea dichotoma is present throughout the entire 300 kyr of mound build-up history, with the exception of MIS 5, and is possibly a key contributor to mound development during glacial periods. The comparison of our observations to other long-term coral mound records demonstrates that western and central Mediterranean coral mounds do not show concurrent build-up over interglacial-glacial cycles, implying that their development may be driven by regional and local environmental forcing., Climate of the Past, 18 (8), ISSN:1814-9324, ISSN:1814-9332

Although lake sediments are globally important organic carbon sinks and therefore important habitats for deep microbial life, the deep lacustrine biosphere has thus far been little studied compared to its marine counterpart. To investigate the impact of the underexplored deep lacustrine biosphere on the sediment geochemical environment and vice versa, we performed a comprehensive microbiological and geochemical characterization of a sedimentary sequence from Lake Cadagno covering its entire environmental history since formation following glacial retreat. We found that both geochemical gradients and microbial community shifts across the ∼13.5 kyr subsurface sedimentary record reflect redox changes in the lake, going from oxic to anoxic and sulfidic. Most microbial activity occurs within the top 20 cm of sediment, where millimolar sulfate concentrations diffusing in from the bottom water are almost completely consumed. In deeper sediment layers, organic carbon remineralization is much slower but microorganisms nonetheless subsist on fermentation, sulfur cycling, metal reduction, and methanogenesis. The most surprising finding was the presence of a deep, oxidizing groundwater source. This water source generates an inverse redox gradient at the bottom of the sedimentary sequence and could contribute to the remineralization of organic matter sequestered in the energy-limited deep subsurface., Frontiers in Earth Science, 9, ISSN:2296-6463

Historical records of trace elements in lake sediments provide source-to-sink information about potentially toxic pollutants across space and time. We investigated two lakes located at different elevations in the Ecuadorian Andes to understand how trace element fluxes are related to (i) geology, (ii) erosion in the watersheds, and (iii) local point sources and atmospheric loads. In remote Lake Fondococha (4150 m a.s.l.), total Hg fluxes stay constant between ca. 1760 and 1950 and show an approximately 4.4-fold increase between pre-1950 and post-1950 values. The post-1950 increase in fluxes of other trace elements (V, Cr, Co, Ni, Cu, Zn, As, Cd, and Pb) is lower (2.1–3.0-fold) than for Hg. Mostly lithogenic sources and enhanced soil erosion contribute to their post-1950 increase (lithogenic contribution: > 85%, Hg: ~ 58%). Average post-1950 Hg fluxes are approximately 4.3 times higher in peri-urban Lake Llaviucu (3150 m a.s.l.) than in the remote Lake Fondococha. Post-1950 fluxes of the other trace elements showed larger differences between Lakes Fondococha and Llaviucu (5.2 < 25–29.5-fold increase; Ni < Pb–Cd). The comparison of the post-1950 average trace element fluxes that are derived from point and airborne sources revealed 5–687 (Hg–Pb) times higher values in Lake Llaviucu than in Lake Fondococha suggesting that Lake Llaviucu’s proximity to the city of Cuenca strongly influences its deposition record (industrial emissions, traffic, caged fishery). Both lakes responded with temporary drops in trace element accumulations to park regulations in the 1970s and 1990s, but show again increasing trends in recent times, most likely caused by increase in vehicular traffic and openings of copper and gold mines around Cajas National Park. Supplementary Information The online version contains supplementary material available at 10.1007/s11356-020-11437-0.

Iron is the most abundant redox-sensitive element on the Earth’s surface, and the oxidation state, mineral host, and crystallinity of Fe-rich phases in sedimentary systems can record details of water-rock interactions and environmental conditions. However, we lack a complete understanding of how these Fe-rich materials are created, maintained, and oxidized or reduced in sedimentary environments, particularly those with mafic sources. The catchment of Lake Towuti, Indonesia, is known to contain a wide range of abundant crystalline Fe oxide, and the lake has a long sedimentary history. Here we study a ∼100 m long drill core from the lake to understand patterns of sedimentation and how young iron-rich sediments are affected by diagenesis through geologic time. We use visible/near infrared and Mössbauer spectroscopy, X-ray diffraction, bulk chemistry measurements, and statistical cluster analysis to characterize the core sediment. We find that the core sediment can be divided into three statistically different zones dominated by Mg serpentine, Al clay minerals, and Fe2+ carbonate, respectively. The entire core is rich in nanophase Fe, and elemental correlations and Fe mineralogy vary between these zones. The nanophase Fe is highly complex with both ferrous and ferric components, and contributes to, but does not dictate, variations in sediment color. We propose that the distinctive zones are the result of structural basin changes (notably river capture and shifting drainage patterns), and diagenetic overprinting caused by deep burial of reactive Fe. This complex record has implications for disentangling depositional and diagenetic trends in other mafic lacustrine systems.

Detailed knowledge about the history of vegetation, fire and land use is scarce in Northern Greece. We analysed lake sediments from Limni Zazari (Northern Greece) to reconstruct the past local vegetation and fire history with a special focus on land use and its impacts on erosion and lake eutrophication. Our data suggest a rather dense steppic vegetation after ca 20,000 cal bp (18050 cal bc). Forest expansion with Pinus sylvestris and admixed Quercus pubescens started around 14,500 cal bp (12550 cal bc). After the onset of the Holocene, mixed deciduous sub-mediterranean oak forests expanded, accompanied by rapidly decreasing soil erosion rates and increasing aquatic biological productivity. Pollen of cereals and Plantago lanceolata suggests continuous farming activities in the region after 8,200 cal bp (6250 cal bc), in agreement with archaeological evidence. Fairly closed mixed pine-oak forests dominated the landscape until ca 3,500 cal bp (1550 cal bc) that were only temporarily reduced during the Neolithic around 7,100 and 6,500 cal bp (5150 and 4550 cal bc). Land cover changes and aquatic biogeochemistry were closely linked during this period. Forest phases corresponded to lake eutrophication and hypolimnetic anoxia (meromixis), whereas during periods of deforestation (e.g. around 8,200 cal bp/6250 cal bc) soil erosion rates and lake mixing increased, while aquatic productivity decreased. After 3,500 cal bp (1550 cal bc) humans disrupted forests and open land vegetation expanded (e.g. Artemisia, Rumex-type, Cichorioideae, Chenopodiaceae). With the onset of the Iron Age (ca. 3,050 cal bp/1100 cal bc) grassland communities expanded massively and pine-oak forests gradually declined. Anthropogenic pressure on forests increased even more during the past 500 years. Finally, forest recovery during the recent decades led to decreased erosion and increased lake productivity. We conclude that over the millennia, intense pastoral and arable activities shaped both aquatic and terrestrial environments, ultimately creating a humanized vegetation mosaic in which the original natural mixed deciduous oak forests only form relict stands. Future climate warming and decreasing anthropogenic pressure may release a rapid spread of mixed deciduous oak forests around Limni Zazari.

Sediments collected from Lake Towuti, an ultramafic-hosted lake in Indonesia, preserve a visible alternating pattern of red and green sediments due to variations in clay mineral and Fe-oxide composition and abundance consistent with changes in iron oxidation state through time. Spectral, mineralogical, and chemical analyses on soils, river, and sediment samples from across the lake and its catchment were carried out to better understand the starting composition of these sediments and the processes that affected them before and after deposition. Despite high Fe abundances in all samples and abundant Fe oxides in lateritic source regions, mineralogical analyses (X-ray diffraction (XRD) and Mossbauer spectroscopy) of the modern lake sediment show almost no well-crystalline iron oxides. In addition, sequential Fe extractions suggest an increasing proportion of easily extractable, poorly crystalline (X-ray amorphous) material with burial depth. XRD, bulk chemistry, and visible-near infrared (VNIR) spectral reflectance measurements demonstrate that clay mineralogy and bulk chemistry can be inferred from VNIR data. These results provide evidence for variations in Fe mineralogy and crystallinity based on location in this source to sink system. Understanding how the mineralogy and chemistry of sediments within a ferruginous lake basin are affected by transport, chemical alteration, physical alteration, and deposition from source to sink on Earth, and the degree to which these trends and underlying processes can be inferred from chemical and spectral properties, may provide useful direction in assessing paleoenvironmental conditions in other terrestrial lakes as well as ancient lacustrine environments preserved in the stratigraphic record of Mars.

The 1601 Common Era earthquake (Mw ca. 5.9) in "Unterwalden", Central Switzerland triggered multiple subaqueous mass movements and a subaerial rockfall that generated tsunami waves with devastating...

Lake Victoria (LV), Africa’s largest lake is situated in the African Great Rift Valley. Due to its shallowness (max.68 m; mean 40 m) and limited river inflow, LV is very sensitive to variations in climate and lake level fluctuations. As a result, LV has undergone repeated low stand periods, or even complete desiccation during the Late Pleistocene with profound effects on the aquatic ecosystem. One example is the emergence of a unique biodiversity of endemic cichlid species following the lake’s last desiccation event during the last glacial and subsequent refilling commencing ~15,000 years ago.In an interdisciplinary project we aim at reconstructing linkages between paleoenvironmental variability, disturbances and adaptive species radiation by combining approaches from paleogenomics, paleoecology and paleolimnology. For this purpose, four sediment cores along a depth-transect (near-shore to offshore), covering ca. the past 14,000 years, are analyzed.We present first paleolimnological results of long-term changes of using (isotope-)geochemical indicators including: Sedimentary pigments and biogenic silica to infer aquatic productivity supported by micro X-ray Fluorescence (XRF) derived element geochemistry, 13C and 15N, and sedimentary phosphorus fraction analyses providing information on changes in sediment composition.The results suggest that the infilling of the LV basin was a long-term step-wise process. This is shown by elevated and variable indicators for lithogenic input (e.g Ti, Zr and K) and interpreted as mobilization of substrate from the shorelines by a dynamic lake level prior to its stabilization in the Early and Mid-Holocene. This process is mainly reflected in the core taken at the greatest water depth (65 m). Simultaneously, the aquatic productivity (BSi and chloropigments) increased rapidly after the refilling of the lake basin in the Late-Glacial. A gradual drying of the climate and a following shift to a more oxygenated water column is observed in the Mid-to Late Holocene indicated by a decline in chemically weathered material (e.g Rb/K & K/Al ratios) and abundance of Mn.

The modern basin of trinational Lake Constance, between Switzerland, Germany, and Austria, represents the underfilled northern part of a glacially overdeepened trough. It is over 400 m deep and reaches well into the Alps at its southern end. The overdeepening was formed by the numerous glacial advance-retreat cycles of the Rhine Glacier throughout the Middle to Late Quaternary. A seismic survey of Lake Constance revealed a Quaternary sediment fill of over 150 m thickness under the modern lake floor in a maximal water depth of >250 m. This sedimentary sequence represents at least the last glacial cycle with ice-contact deposits at the base on top of the Molasse bedrock overlain by glaciolacustrine to lacustrine sediments. During the successful field test of a newly developed mid-size coring system ("HIPERCORIG"), the longest core ever taken in Lake Constance was recovered with an overall length of 24 m. The drill core, taken in a water depth of 200 m, consists of a nearly continuous succession of lacustrine sediments including over 12 m of pre-Holocene sediment at the base. The entire core was petrophysically and geochemically analyzed, sedimentologically described, and 14 lithotypes were identified. In combination with a 14C- and OSL-based age-depth model, the core was divided into three main chronostratigraphic units. The basal age of ~13.7 ka BP places the base of the section back into the Bølling-Allerød interstadial whereas the overlying strata represent a complete Younger-Dryas and Holocene section.The sediments offer a high-resolution insight into the evolution of Paleolake Constance from a cold postglacial to a more productive warm Holocene lake. The Late Glacial sections are dominated by massive, m-thick sand beds reflecting episodic sedimentation pulses. They are most likely linked with a subaquatic channel system that is still apparent in today's lake bathymetry despite the Holocene drape. This channel system was fed from a Late Glacial river from the north; provenance analysis of the initially unexpected sands together with hydrologic considerations will document whether this inflowing high-discharge river represented a local catchment (i.e. northern lake shore) or an Alpine signal (i.e. from the south) provided by the Rhine glacier. Tentative pore water hydrogeochemical and isotope analyses indicate a still active flow system at depth. The overlying Holocene section reveals a prominent, several cm-thick double-turbiditic event layer representing the most distal impact of the "Flimser Bergsturz", the largest known rock slide of the Alps that occurred over 100 km upstream the Rhine River at ~9.5 ka BP. Furthermore, lithologic variations in the Holocene section document the varying sediment load of the Rhine and of the endogenic production representing a multitude of environmental changes.

Lake Cadagno is a meromictic Alpine lake located in the Piora Valley, Switzerland. In 2019, a 10,000-year (10 m)sediment sequence was collected and found to contain three main lithological units: glacial sediment deposited under oxic conditions; a Mn-rich and organic-matter-rich sediment layer deposited during the transition from an oxic late-glacial lake to the onset of anoxia, and dark, sulfidic sediments deposited during the period of euxinia to the present. This study investigates the relationships between the physical-chemical properties and microorganisms of the sediment sequenceusing genome-resolved and targeted metagenomics. Results show that 16S rRNA gene abundance peaks in upper 1-32 cm of the sediment core (108 copies per gram of sediment) and decreases with depth. The abundance of a marker gene for sulfate reduction, dsrB, is positively correlated to 16S rRNA gene copy numbers, decreasing with depth from approximately 108 copies per gram of sediment in the top 30 cm to 104 gene copies per gram of sediment at 900 cm below the sediment depth. These results suggest that sulfate-reducing microbial communities in surface sediments harvest the bioavailable oxidized sulfur inorganic species. In contrast, the presence of sulfate-reducing genes in sediments with sulfate concentrations below detection may indicate the engagement of microbial populations in sulfur cycling using alternative metabolic strategies (e.g. secondary fermentation). Moreover, a clear differentiation between surface and deep sediment communities is observed. Sequencing of dsrB amplicons show a decrease in dsrB sequence richness with depth and sediment age. A clear transition from a surface section dominated (>80% relative abundance) by Deltaproteobacteria-related dsrB sequences from well-studied groups, to a deeper section below 40 cm dominated by a group of unclassified dsrB sequences most likely related to Firmicutes or Chloroflexi is also observed. The identity of these unclassified dsrB sequences will be determined by genome-resolved metagenomic sequencing (currently in progress). Furthermore, these analyses will give information on the presence of complete sulfate-reduction pathways and/or genes related to sulfur cycling in these microbial groups. By reconstructing the genomes of sulfate reducers and other microbial populations throughout the core, we will investigate whether there are genomic changes associated with the main geochemical trends. This work will enable us to assess the influence of a changing lake with the evolution of sediment-dwelling prokaryotic populations over thousands of years.

Climate affects the mineralogy and grain size of sediments deposited in lakes. These properties are reflected in the sediment magnetic properties and can be characterized using magnetic methods. As part of the Cadagno-Project, which recovered several gravity and piston cores spanning the entire lake history from the deglacial to the present from the deepest part of permanently stratified Lake Cadagno, which is due to its peculiar water column chemistry considered an early Earth ocean analogue, our study aims to define changes in climate conditions during sedimentation. Here, we present a rock magnetic dataset (low-field magnetic susceptibility and its temperature dependence, anhysteretic and isothermal remanent magnetization (ARM, IRM), acquired in various fields, AF demagnetization, and hysteresis loops) that helps characterize the concentration, mineralogy, and grain size of magnetic carriers, and their variability with depth. Susceptibility, ARM, and IRM were measured on core sediments down to a depth of 886 cm below the lake bottom, providing a high-resolution record of the sedimentary environment of Lake Cadagno over the last 11,000 years. In addition to these depth profiles, detailed rock magnetic experiments were conducted at specific depths. The cores consist of pelagic sediments, flood turbidites, and late glacial sediments. In order to determine the characteristics of the background sedimentation, only turbidite-free intervals were included in this study. The depth profiles of susceptibility, ARM and IRM have approximately similar variations with depth. They show distinct peaks at the upper parts of the pelagic sediments (156-158 cm below the lake bottom, ̴1280-1320 cal. Yr Bp) and of the late glacial sediments (826-844 cm below the lake bottom), which can be interpreted as increased concentration of ferromagnetic minerals or as a change in the magnetic mineralogy, in addition to decreasing trend in the background. Several intervals within the pelagic sediments are dominated by low-coercivity minerals (

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.

Molybdenum (Mo) isotopes are known as sensitive recorders for changes in redox conditions because the oxidized form of Mo (Mo VI) is more soluble, whereas its reduced form is more particle reactive. Previous studies suggest that Mo isotopic fractionation during the weathering process is controlled by atmospheric input, Mo host, and bedrock composition. However, Mo isotopic variation and processes influencing fractionation in weathering profiles overlying ultramafic bedrock, the early Earth analog, have yet to be explored. This study explores for the first time (1) Mo behavior and (2) isotopic fractionation in two representative and intensely-weathered lateritic profiles overlying ultramafic bedrock of the East Sulawesi Ophiolite, Indonesia. Mo concentrations measured on samples obtained from laterite successions studied here range between 60 - 537 ppb and are overall higher compared to bedrock values ranging between 9 - 45 ppb. The Mo isotope compositions of laterite samples vary between -0.043‰ to -0.161‰ δ98MoNIST3134. The overall close to mantle Mo isotopic composition of the laterite samples, their small Mo isotope variability, and the covariation between Mo and Ti concentrations suggest low mobility of Mo during chemical weathering and laterite formation. This low Mo mobility is likely a consequence of a) the low Mo concentration of the ultramafic protolith and b) adsorption of Mo to secondary Fe-Oxides during laterite formation under oxic weathering conditions.

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.

Global spread of anoxia in aquatic ecosystems has become a major issue that may potentially worsen due to global warming. The reconstruction of long-term hypolimnetic anoxia records can be challenging due to lack of valid and easily measurable proxies. The sedimentary Mn/Fe ratio measured by X-ray fluorescence (XRF) is often used as a proxy for past lake redox conditions. Yet the interpretation of this ratio can be problematic when Fe and Mn accumulation is not solely redox driven. We used the varved sediments of Lake Moossee (Switzerland) to examine the partitioning of Fe and Mn in seven fractions by sequential extraction under various oxygen conditions over the last 15,000 years. We combined this data with XRF scans and an independent diagnostic proxy for anoxia given by a hyperspectral imaging (HSI)-inferred record of bacteriopheophytin, to validate the use of the XRF-Mn/Fe ratio as redox proxy. In the 15,000-year long record, Fe was bound to humins and amorphous, crystalline, sulfide and residual forms. Mn was mainly present in carbonate and amorphous forms. Higher erosion, prolonged anoxia, diagenesis and humic matter input affected Fe and Mn accumulation. Under holomixis the XRF-Mn/Fe ratio successfully reflected lake redox conditions. Periods with higher detrital Fe input obscured the applicability of the ratio. During phases of permanent anoxia, intensified early diagenetic processes trapped Mn in the sediments in carbonate, crystalline oxide and humic forms. Our study shows that the single use of the XRF-Mn/Fe ratio is often not conclusive for inferring past lake redox conditions. The application of the XRF-Mn/Fe as a proxy for anoxia requires taking into account the individual lake characteristics and changes in lake environmental conditions, which affect the accumulation of Fe and Mn in the sediments., Science of The Total Environment, 755 (Part 2), ISSN:0048-9697, ISSN:1879-1026

The 1601 CE earthquake (Mw ca. 5.9) in “Unterwalden,” Central Switzerland, triggered multiple subaqueous mass movements and a subaerial rockfall that generated tsunami waves with run-up heights of up to 4 m and several hundred meters of inundation along the coastal lowlands of Lake Lucerne. In the shallow Lucerne Bay, historical chronicles reported an oscillation of the water with an initial amplitude of ∼1–2 m and a period of 10 min, which continued for several days after the event with decreasing amplitude. Here, we investigate the lake-tsunami process chain from subaqueous mass movement-generated tsunami to wave propagation and ultimately to sediment resuspension, transport, and deposition in the shallow-water environment. The effects of the historical tsunami on Lucerne Bay are reconstructed using sediment-core analysis and numerical simulation of wave propagation. A 60-cm-thick event deposit was recovered along a sediment-core transect in the shallow waters and radiocarbon dated to 1306–1442 cal CE. The event deposit has a sharp basal contact with carbonate shell fragments followed upwards a normally graded succession of siliciclastic sand to silt with a high proportion of horizontally bedded wooden particles. The numerically simulated tsunami waves are characterized by a water-surface displacement of up to 1.5 m and generate bed shear-stresses that are likely capable of remobilizing large amounts of sediments in the Lucerne Bay area. Our study successfully links the sedimentology of event deposits with physical principles of sediment mobilization derived from numerical wave-forward modeling, providing a tool to improve the identification and interpretation of potential tsunami deposits., Geochemistry, Geophysics, Geosystems, 22 (12), ISSN:1525-2027

The Opalinus Clay is an argillaceous to silty mudstone formation, notable in Switzerland as the selected host rock for deep geological disposal of radioactive waste. Its upper bounding unit (Passwang Formation and eastern equivalents) is composed of successions of mudstone, sandy bioclastic marl and limestone separated by ooidal ironstone beds. The lithostratigraphic transition is diachronous across northern Switzerland and shows high vertical and lateral lithological variability. To constrain this variability into predictive models, and to identify horizons with properties that could potentially influence radionuclide mobility, the sedimentological and diagenetic processes involved in the genesis of this transition have to be investigated. The present study aims at testing the applicability of X-ray fluorescence chemostratigraphy to characterise the mixed carbonate-siliciclastic units and understand the complex genesis of the lithostratigraphic transition from the Opalinus Clay towards its upper bounding unit. Sediment drill cores from four locations across northern Switzerland (Mont Terri, Riniken, Weiach and Benken) are analysed using high-resolution X-ray fluorescence core scanning. Data are compared to petrographic and additional geochemical data sets (inductively coupled plasma mass spectrometry, scanning electron microscopy with energy dispersive X-ray analysis, micro-X-ray fluorescence mapping) obtained from powdered samples, thin section analyses and drill core slabs. The results demonstrate that the combination of these rapid and non-destructive measurements along with multivariate data analysis allows the fast and objective classification of lithofacies along complex sedimentary successions. Moreover, it provides quantitative means for differentiating between prominent depositional and post-depositional processes. The lithostratigraphic transition has been traced by the use of specific elemental proxies as a discontinuity, and its genesis linked to sediment bypassing., The Depositional Record, 7 (1), ISSN:2055-4877

Global spread of hypoxia and less frequent mixing in lakes is a major growing environmental concern. Climate change and human impact are expected to increasingly deteriorate aquatic ecosystems. The study of processes and drivers of such changes in the past provides a great asset for prevention and remediation in the future. We used a multiproxy approach combining high-resolution bulk pigment data measured by hyperspectral imaging (HSI) with lower-resolution specific chlorophyll types and carotenoids measured by HPLC to examine Holocene trophic state changes and anoxia evolution in the meromictic Lake Jaczno, NE Poland. A redundancy analysis (RDA) including pollen-inferred vegetation cover, temperature and human impacts provides insight into specific conditions and drivers of changing trophic and redox states in the lake. Anoxic and sulfidic conditions were established in Lake Jaczno after initial basin infilling 9500 years ago. Until 6700 cal BP, lake trophy was relatively low, water turbidity was high and green sulfur bacteria (GSB) were abundant within the phototrophic community, suggesting a deep oxic–anoxic boundary and weak stratification. The period between 6700–500 cal BP is characterized by constantly increasing lake production and a gradual shift from GSB to purple sulfur bacteria (PSB), suggesting a shallower oxic–anoxic boundary and pronounced stratification. Yet, the presence of spheroidene and speroidenone in the sediments indicates intermittent anoxia. After 500 cal BP, increasing human impact, deforestation and intensive agriculture promoted lake eutrophication, with a shift to PSB dominance and establishment of permanent anoxia and meromixis. Our study unambiguously documents the legacy of human impact on processes determining eutrophication and anoxia.