Riethdorf, Jan-Rainer (2008) Cold-water coral Lophelia pertusa as a high-resolution archive of paleoenvironmental conditions in the central Mediterranean. (Diploma thesis), Christian-Albrechts-Universität, Kiel, 126 pp.

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Abstract

Cold-water corals are one of the most promising paleoenvironmental archives in paleoclimate research that contain high-resolution records of long-term climate change. This study focuses on fossil and recent specimens of the cold-water coral Lophelia pertusa from the Mediterranean Sea as well as on water samples from different locations in the central Mediterranean, the Norwegian Sea and the NE-Skagerrak. The intention is to apply established geochemical proxies of seawater temperatures and to compare present-day with paleoenvironmental conditions during the late glacial period and the Younger Dryas cold interval. Electron-probe imaging is used to map elemental distributions of Mg, Ca, Sr and S across the thecal wall of the coralline aragonite and to generate high-resolution profiles of molar element ratios. Water samples were collected together with the coral specimens and are analyzed using ICP-MS- and ICP-OES-techniques to determine concentrations of major and trace elements. Fossil coral samples were U/Th-dated after having been checked for alteration. Additionally, measurements of stable carbon (δ13C) and stable oxygen (δ18O) isotopes conducted on the same specimens by Matthias López Correa at GZNIPAL, Erlangen, are evaluated. High-resolution records of Mg/Ca-, Sr/Ca- and S/Ca-ratios are investigated using spectral analysis. Paleotemperatures are reconstructed using Sr/Ca-ratios and the ”lines technique”-method (Smith et al., 2000). Furthermore, the geochemistry of the recent coral skeletons are compared and calibrated to the analysed water samples in order to reconstruct paleowater-values with the focus lying on Mg/Ca-, Sr/Ca-, S/Ca- and B/Ca-ratios. Results regarding element incorporation in coral skeletons can be interpreted by means of biologically controlled calcification processes and by influence of environmental parameters. S/Ca-ratios are suggested to be influenced by temperature, primary productivity and/or ventilation of intermediate water masses. Reconstructed temperatures are different for both methods applied, indicating lower temperatures than at present at 17.6 ka and at 12.4 ka, and that regional Sr/Ca-calibrations are needed for L. pertusa. Salinity accounts for most of the observed seawater concentrations of major and trace elements, except for antimony and barium, which might be influenced by primary productivity. Finally, results indicate that cold-water corals colonize the Mediterranean Sea during cold climates and that low latitude ecosystems act as glacial refugia in the deep sea.

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