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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 19 | Copyright
Biogeosciences, 15, 5909-5928, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 08 Oct 2018

Research article | 08 Oct 2018

Coastal primary productivity changes over the last millennium: a case study from the Skagerrak (North Sea)

Anna Binczewska1, Bjørg Risebrobakken2, Irina Polovodova Asteman2,a, Matthias Moros3, Amandine Tisserand2, Eystein Jansen2,4, and Andrzej Witkowski1 Anna Binczewska et al.
  • 1Faculty of Geosciences, University of Szczecin, Szczecin, Poland
  • 2Uni Research Climate, Bjerknes Centre for Climate Research, Bergen, Norway
  • 3Leibniz Institute for Baltic Sea Research (IOW), Warnemünde, Germany
  • 4Department of Earth Science, University of Bergen, Norway
  • acurrently at: Marin Mätteknik (MMT) Sweden AB, Gothenburg, Sweden

Abstract. A comprehensive multi-proxy study on two sediment cores from the western and central Skagerrak was performed in order to detect the variability and causes of marine primary productivity changes in the investigated region over the last 1100 years. The cores were dated by Hg pollution records and AMS 14C dating and analysed for palaeoproductivity proxies such as total organic carbon, δ13C, total planktonic foraminifera, benthic foraminifera (total assemblages as well as abundance of Brizalina skagerrakensis and other palaeoproductivity taxa) and palaeothermometers such as Mg∕Ca and δ18O. Our results reveal two periods with changes in productivity in the Skagerrak region: (i) a moderate productivity at  ∼ CE900–1700 and (ii) a high productivity at  ∼ CE1700–present. During  ∼ CE900–1700, moderate productivity was likely driven by the nutrients transported with the warm Atlantic water inflow associated with a tendency for a persistent positive NAO phase during the warm climate of the Medieval Climate Anomaly, which continues into the LIA until  ∼ CE1450. The following lower and more variable temperature period at  ∼ CE1450–1700 was likely caused by a reduced contribution of warm Atlantic water, but stronger deep-water renewal, due to a generally more negative NAO phase and a shift to the more variable and generally cooler climate conditions of the Little Ice Age. The productivity and fluxes of organic matter to the seafloor did not correspond to the temperature and salinity changes recorded in the benthic Melonis barleeanus shells. For the period from  ∼ CE1700 to the present day, our data point to an increased nutrient content in the Skagerrak waters. This increased nutrient content was likely caused by enhanced inflow of warm Atlantic water, increased Baltic outflow, intensified river runoff, and enhanced human impact through agricultural expansion and industrial development. Intensified human impact likely increased nutrient transport to the Skagerrak and caused changes in the oceanic carbon isotope budget, known as the Suess effect, which is clearly visible in our records as a negative shift in δ13C values from  ∼ CE1800. In addition, a high appearance of S. fusiformis during the last 70 years at both studied locations suggests increased decaying organic matter at the sea floor after episodes of enhanced primary production.

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Primary productivity is an important factor in the functioning and structuring of the coastal ecosystem. Thus, two sediment cores from the Skagerrak (North Sea) were investigated in order to obtain a comprehensive picture of primary productivity changes during the last millennium and identify associated forcing factors (e.g. anthropogenic, climate). The cores were dated and analysed for palaeoproductivity proxies and palaeothermometers.
Primary productivity is an important factor in the functioning and structuring of the coastal...