Articles | Volume 14, issue 23
Biogeosciences, 14, 5607–5632, 2017
Biogeosciences, 14, 5607–5632, 2017

Research article 12 Dec 2017

Research article | 12 Dec 2017

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 Fanget5,6, Nadine Quintana Krupinski7, Odile Peyron8, Anna Stepanova9, Jonathan Warnock10, Niels A. G. M. Van Helmond11, Benjamin H. Passey12, Ole Rønø Clausen5, Ole Bennike13, Elinor Andrén14, Wojciech Granoszewski15, Thomas Andrén14, Helena L. Filipsson7, Marit-Solveig Seidenkrantz5, Caroline P. Slomp11, and Thorsten Bauersachs16 Ulrich Kotthoff et al.
  • 1Institute for Geology, University of Hamburg, 20146, Hamburg, Germany
  • 2Center of Natural History, University of Hamburg, 20146, Hamburg, Germany
  • 3MARUM, Center for Marine Environmental Sciences, University of Bremen, 28359, Bremen, Germany
  • 4Department of Earth, Planetary, and Space Sciences, UCLA, Los Angeles, 90024, USA
  • 5Centre for Past Climate Studies, Department of Geoscience, Aarhus University, 8000 Aarhus C, Denmark
  • 6Centre de formation et de recherche sur les environnements méditerranées, Université de Perpignan, 66860 Perpignan CEDEX, France
  • 7Department of Geology, Lund University, 22362 Lund, Sweden
  • 8Institute of Evolutionary Sciences, UMR 5554, University of Montpellier, 34095 Montpellier CEDEX 05, France
  • 9Department of Computer Science and Engineering, Texas A&M University, College Station, 77843, USA
  • 10Department of Geoscience, Indiana University of Pennsylvania, Indiana, 15705, USA
  • 11Department of Earth Sciences – Geochemistry, Faculty of Geosciences, Utrecht University, P.O. Box 80021, 3508 TA Utrecht, the Netherlands
  • 12Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, 48109, USA
  • 13Geological Survey of Denmark and Greenland, 1350 Copenhagen, Denmark
  • 14School of Natural Sciences, Technology and Environmental Studies, Södertörn University, 14189 Huddinge, Sweden
  • 15Polish Geological Institute-National Research Institute Krakow, 31-560 Kraków, Poland
  • 16Christian-Albrechts-Universität, Institute of Geosciences, Department of Organic Geochemistry, 24118 Kiel, Germany

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 and northern Europe. Such studies contribute to a better understanding of how environmental parameters change in continental shelf seas and enclosed basins. Here we present a multi-proxy-based reconstruction of paleotemperature (both marine and terrestrial), paleosalinity, and paleoecosystem changes from the Little Belt (Site M0059) over the past  ∼  8000 years and evaluate the applicability of inorganic- and organic-based proxies in this particular setting.

All salinity proxies (diatoms, aquatic palynomorphs, ostracods, diol index) show that lacustrine conditions occurred in the Little Belt until  ∼  7400 cal yr BP. A connection to the Kattegat at this time can thus be excluded, but a direct connection to the Baltic Proper may have existed. The transition to the brackish–marine conditions of the Littorina Sea stage (more saline and warmer) occurred within  ∼  200 years when the connection to the Kattegat became established after  ∼  7400 cal yr BP. The different salinity proxies used here generally show similar trends in relative changes in salinity, but often do not allow quantitative estimates of salinity.

The reconstruction of water temperatures is associated with particularly large uncertainties and variations in absolute values by up to 8 °C for bottom waters and up to 16 °C for surface waters. Concerning the reconstruction of temperature using foraminiferal Mg  /  Ca ratios, contamination by authigenic coatings in the deeper intervals may have led to an overestimation of temperatures. Differences in results based on the lipid paleothermometers (long chain diol index and TEXL86) can partly be explained by the application of modern-day proxy calibrations to intervals that experienced significant changes in depositional settings: in the case of our study, the change from freshwater to marine conditions. Our study shows that particular caution has to be taken when applying and interpreting proxies in coastal environments and marginal seas, 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.

Short summary
We present reconstructions of paleotemperature, paleosalinity, and paleoecology from the Little Belt (Site M0059) over the past ~ 8000 years and evaluate the applicability of numerous proxies. Conditions were lacustrine until ~ 7400 cal yr BP. A transition to brackish–marine conditions then occurred within ~ 200 years. Salinity proxies rarely allowed quantitative estimates but revealed congruent results, while quantitative temperature reconstructions differed depending on the proxies used.
Final-revised paper