From lacustrine carbonates to paleohydrology - how robust are our proxies?

• Applicant: Professorin Dr. Ola Kwiecien
• Subject Area: Palaeontology
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 268985795

Lacustrine carbonates, authigenic (here defined as: non-detrital, precipitated from solution either abiotically or through a biologically-mediated process) and biogenic (skeletal), represent highly significant archives of past continental climate change. Proxies used include light stable isotopes (d18O, d13C) and major and trace elements (Ca, Mg, Sr). These allow for an assessment of past hydrological changes. Pending diagenetic alteration, the use of these proxy data, however, is hindered by multiple controls of preserved signals, often related to specific regional or even local settings. Disentangling the role of global, regional and local factors influencing lacustrine carbonate chemistry and extracting the exact mechanism of observed changes presents a challenge to paleoclimate community. Here, I propose a process-oriented research project exploring the strengths and limitations of stable light isotope and element chemistry of biogenic (ostracod valves) and authigenic carbonates as hydrological proxies in lake system. As such this research does not focus on climate reconstructions per se but intends to build more reliable and quantitative fundaments for advanced proxy interpretations. For this purpose I have carefully chosen the archive; well-dated sediments from terminal, alkaline Lake Van (eastern Anatolia, Turkey) which cover the full last glacial/interglacial cycle (140 ka) and document high amplitude salinity changes (local signal) superimposed on millennial-scale variability reflecting D/O oscillations (hemispheric signal). The main goal of the project - a comprehensive approach to the lacustrine carbonate system - will be achieved by comparing and contrasting the chemistry of biogenic (ostracods) and authigenic carbonate fractions retrieved from the same stratigraphic horizon. Analytical work includes d18O and d13C ratios and major and trace elemental (Ca, Mg, Sr) analysis, scanning electron microscope (SEM) imaging, X-ray diffractiometry (XRD) and laboratory precipitation experiments. While the combined taxonomic and chemical approach will test the versatility of ostracod as paleoenvironmental indicators, a series of laboratory precipitation experiments will verify chemistry and mineralogy of authigenic carbonate samples collected from the Lake Van profile. Ultimately, this project has a high potential to provide a better understanding of carbonate chemistry and quantitative reconstruction of carbonate-inferred parameters (salinity, temperature, precipitation-to-evaporation ratio) in paleolacustrine settings.

• DFG Programme: Research Grants