Abteilung Oberflächengewässer

Environmental sciences depend heavily on observational data. Successful studies of ecological processes in lakes require in-situ data that cover the relevant temporal scales from milliseconds to entire seasons. Temporal and spatial coverage requirements represent a non-trivial challenge in lake sciences, which have traditionally used sampling campaigns conducted from research vessels or anchored moorings. These come with various logistical tasks and impose constraints on data coverage. An open water platform can overcome many of these limitations by providing continuous access and a wide range of analytical capabilities in direct contact with the lake environment. A consortium of five partner institutions constructed a 10 × 10 m, open-water, multipurpose platform on Lake Geneva (Switzerland/France) for a broad range of limnological research. The LéXPLORE platform, anchored since February 2019 at a position reaching 110 m depth off the lake's north-shore, provides workspace for a large number of instruments and up to 16 staff working in parallel on individual or integrated multidisciplinary projects. The safe, dry and protected floating laboratory offers direct access to the lake environment for high-sensitivity, high-throughput analyses including those which might advance sensor technology. The platform provides flexible workspace for both high-resolution measurements and investigations of larger-scale external forcing. It thus supports multidisciplinary empirical research in limnology, atmospheric sciences, and remote sensing. This article describes the platform and how it will advance aquatic sciences. The large number of projects that have already requested access to the platform demonstrate the efficacy and necessity of the LéXPLORE concept.

We here estimate past temperature and hydroclimate variations in eastern Anatolia for marine isotope stages 4 to 1 (MIS4 to MIS1) respectively using branched glycerol dialkyl glycerol tetraethers (brGDGTs) and the hydrogen isotopic composition of n-C₂₉ leaf-wax n-alkanes (δ²H_wax) stored in the sedimentary record of Lake Van (Turkey). Our millennial-scale lipid biomarker records reflect warm and wet conditions during interstadials/interglacials and colder and dryer periods with increased evapotranspiration and aridity during stadials/glacials. The degree of methylation of the 5-methyl brGDGTs (MBT´_5me) indicates increasing mean annual air temperatures (MAT) during stadial/interstadial transitions, that characterize Dansgaard-Oeschger events, and during the last glacial termination.
Based on the effects of changes in precipitation amount on apparent enrichment factors between the δ²H of the C₂₉n-alkanes and δ²H of precipitation, a total increase in annual precipitation of about 200 mm during transitions from stadials to interstadials, and of 300-350 mm during glacial-interglacial transitions can be determined, in line with previous paleoclimate reconstructions for the Eastern Mediterranean.
High sterol concentrations in sediments deposited during warm and humid interstadials reflect increases in lake level, vegetation density and algal blooms, whereas lower values of the branched versus isoprenoid tetraethers ratio (BIT) likely reflects the increased niche of Thaumarchaeota resulting from enhanced windiness and mixing of the water column during colder periods. This quantitative hydroclimate reconstruction from Lake Van (Turkey), as it is optimally situated to respond to North Atlantic climate change via changes in the large-scale wind fields shed light into millennial-scale global climate variability.