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Journal of Micropalaeontology An open-access journal of The Micropalaeontological Society
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Volume 37, issue 2
J. Micropalaeontol., 37, 403-429, 2018
https://doi.org/10.5194/jm-37-403-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
J. Micropalaeontol., 37, 403-429, 2018
https://doi.org/10.5194/jm-37-403-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Sep 2018

Research article | 07 Sep 2018

Assessing proxy signatures of temperature, salinity, and hypoxia in the Baltic Sea through foraminifera-based geochemistry and faunal assemblages

Jeroen Groeneveld1,2, Helena L. Filipsson2, William E. N. Austin3,4, Kate Darling3,5, David McCarthy3, Nadine B. Quintana Krupinski2, Clare Bird5,6, and Magali Schweizer5,7 Jeroen Groeneveld et al.
  • 1Center for Marine Environmental Sciences (MARUM), University of Bremen, Klagenfurter Strasse 2–4, 28359 Bremen, Germany
  • 2Department of Geology, Lund University, Sölvegatan 12, 223 62 Lund, Sweden
  • 3School of Geography and Sustainable Development, University of St. Andrews, North Street, St. Andrews, KY16 9AL, UK
  • 4Scottish Association for Marine Science, Scottish Marine Institute, Oban, PA37 1AQ, UK
  • 5School of Geosciences, University of Edinburgh, James Hutton Road, Edinburgh, EH9 3FE, UK
  • 6Biological and Environmental Sciences, University of Stirling, Stirling, FK9 4LA, UK
  • 7LPG-BIAF UMR CNRS 6112, University of Angers, 2 bd Lavoisier, 49045 Angers CEDEX 01, France

Abstract. Current climate and environmental changes strongly affect shallow marine and coastal areas like the Baltic Sea. This has created a need for a context to understand the severity and potential outcomes of such changes. The context can be derived from paleoenvironmental records during periods when comparable events happened in the past. In this study, we explore how varying bottom water conditions across a large hydrographic gradient in the Baltic Sea affect benthic foraminiferal faunal assemblages and the geochemical composition of their calcite tests. We have conducted both morphological and molecular analyses of the faunas and we evaluate how the chemical signatures of the bottom waters are recorded in the tests of several species of benthic foraminifera. We focus on two locations, one in the Kattegat (western Baltic Sea) and one in Hanö Bay (southern Baltic Sea). We show that seawater Mn∕Ca, Mg∕Ca, and Ba∕Ca (Mn∕Casw, Mg∕Casw, and Ba∕Casw) variations are mainly controlled by dissolved oxygen concentration and salinity. Their respective imprints on the foraminiferal calcite demonstrate the potential of Mn∕Ca as a proxy for hypoxic conditions, and Ba∕Ca as a proxy for salinity in enclosed basins such as the Baltic Sea. The traditional use of Mg∕Ca as a proxy to reconstruct past seawater temperatures is not recommended in the region, as it may be overprinted by the large variations in salinity (specifically on Bulimina marginata), Mg∕Casw, and possibly also the carbonate system. Salinity is the main factor controlling the faunal assemblages: a much more diverse fauna occurs in the higher-salinity ( ∼ 32) Kattegat than in the low-salinity ( ∼ 15) Hanö Bay. Molecular identification shows that only Elphidium clavatum occurs at both locations, but other genetic types of both genera Elphidium and Ammonia are restricted to either low- or high-salinity locations. The combination of foraminiferal geochemistry and environmental parameters demonstrates that in a highly variable setting like the Baltic Sea, it is possible to separate different environmental impacts on the foraminiferal assemblages and therefore use Mn∕Ca, Mg∕Ca, and Ba∕Ca to reconstruct how specific conditions may have varied in the past.

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Current climate and environmental changes strongly affect shallow marine and coastal areas like the Baltic Sea. The combination of foraminiferal geochemistry and environmental parameters demonstrates that in a highly variable setting like the Baltic Sea, it is possible to separate different environmental impacts on the foraminiferal assemblages and therefore use chemical factors to reconstruct how seawater temperature, salinity, and oxygen varied in the past and may vary in the future.
Current climate and environmental changes strongly affect shallow marine and coastal areas like...
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