Reconstructing Holocene temperature and salinity variations in the western Baltic Sea region: A multi-proxy comparison from the Little Belt (IODP Expedition 347, Site M0059)
Ulrich Kotthoff1,2, Jeroen Groeneveld3, Jeanine L. Ash4, Anne-Sophie Fanget5, Nadine Quintana Krupinski6, Odile Peyron7, Anna Stepanova8, Jonathan Warnock9, Niels A. G. M. Van Helmond10, Benjamin H. Passey11, Ole Rønø Clausen5, Ole Bennike12, Elinor Andrén13, Wojciech Granoszewski14, Thomas Andrén13, Helena L. Filipsson6, Marit-Solveig Seidenkrantz5, Caroline P. Slomp10, and Thorsten Bauersachs151Institute for Geology, University of Hamburg, D-20146, Hamburg, Germany 2Center of Natural History, University of Hamburg, Hamburg, D-20146, Germany 3MARUM, Center for Marine Environmental Sciences, University of Bremen, D-28359, Bremen, Germany 4Department of Earth, Planetary, and Space Sciences, UCLA, 90024, USA 5Centre for Past Climate Studies, Department of Geoscience, Aarhus University, 8000 Aarhus C, Denmark 6Department of Geology, Lund University, 22362 Lund, Sweden 7Institut des Sciences de l'Évolution, UMR 5554, Université de Montpellier, 34095 Montpellier cedex 05, France 8Department of Computer Science and Engineering, Texas A&M University, 77843, USA 9Department of Geoscience, Indiana University of Pennsylvania, 15705, USA 10Department of Earth Sciences – Geochemistry, Faculty of Geosciences, Utrecht University. PO Box 80021, 3508 TA Utrecht, Netherlands 11Department of Earth and Environmental Sciences, University of Michigan, 48109, USA 12Geological Survey of Denmark and Greenland, 1350 Copenhagen, Denmark 13School of Natural Sciences, Technology and Environmental Studies, Södertörn University, SE-14189 Huddinge, Sweden 14Polish Geological Institute-National Research Institute Krakow, 31-560 Krakow, Poland 15Christian-Albrechts-University, Institute of Geosciences, Department of Organic Geochemistry, 24118 Kiel, Germany
Received: 21 Mar 2017 – Accepted for review: 26 Mar 2017 – Discussion started: 29 Mar 2017
Abstract. Sediment records recovered from the Baltic Sea during Integrated Ocean Drilling Program Expedition 347 provide a unique opportunity to study paleoenvironmental and -climate change in central/northern Europe. Such studies contribute to a better understanding of how environmental parameters change in continental shelf seas and enclosed basins. We present a multi-proxy-based reconstruction of paleotemperature (both marine and terrestrial), -salinity, and -ecosystem changes from the Little Belt (Site M0059) over the past ~ 8000 years, and evaluate the applicability of inorganic and organic proxies in this particular setting. Salinity proxies (diatoms, aquatic palynomorphs, ostracods, long chain diol index – LDI) show that lacustrine conditions occurred in the Little Belt until ~ 7400 cal. yr BP. A connection to the Kattegat at this time can be excluded, but a direct connection to the Baltic Proper may have existed. The transition to the brackish-marine conditions (more saline and warmer) of the Littorina Sea stage occurred within ~ 200 yr when the connection to the Kattegat became established (~ 7400 cal. yr BP). The different salinity proxies used here show similar trends in relative changes in salinity, but do often not allow quantitative estimates of salinity. The reconstruction of water temperatures is associated with particular large uncertainties and variations in absolute values by up to 8 °C for bottom waters and even up to 16 °C for summer surface waters. Concerning the foraminiferal Mg/Ca reconstruction, contamination in the deeper intervals may have led to an over-estimation of temperatures. Differences in results based on the lipid proxies (LDI and TEXL86) can partly be explained by the application of modern-day proxy calibrations in areas which experienced significant changes in depositional settings, in case of our study e.g. change from freshwater to marine conditions. Our study shows that particular caution has to be taken when applying and interpreting proxies in coastal environments, where water mass conditions can experience more rapid and larger changes than in open-ocean settings. Approaches using a multitude of independent proxies may thus allow a more robust paleoenvironmental assessment.
Kotthoff, U., Groeneveld, J., Ash, J. L., Fanget, A.-S., Quintana Krupinski, N., Peyron, O., Stepanova, A., Warnock, J., Van Helmond, N. A. G. M., Passey, B. H., Clausen, O. R., Bennike, O., Andrén, E., Granoszewski, W., Andrén, T., Filipsson, H. L., Seidenkrantz, M.-S., Slomp, C. P., and Bauersachs, T.: Reconstructing Holocene temperature and salinity variations in the western Baltic Sea region: A multi-proxy comparison from the Little Belt (IODP Expedition 347, Site M0059), Biogeosciences Discuss., doi:10.5194/bg-2017-101, in review, 2017.