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https://doi.org/10.5194/bg-2020-24
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-24
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 29 Jan 2020

Submitted as: research article | 29 Jan 2020

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This preprint is currently under review for the journal BG.

The impact of intertidal areas on the carbonate system of the southern North Sea

Fabian Schwichtenberg1, Johannes Pätsch1,5, Michael Ernst Böttcher2,3,4, Helmuth Thomas5, Vera Winde2, and Kay-Christian Emeis5 Fabian Schwichtenberg et al.
  • 1Theoretical Oceanography, University Hamburg, D-20146 Hamburg, Bundesstr. 53, Germany
  • 2Geochemistry & Isotope Biogeochemistry Group, Department of Marine Geology, Leibniz Institute of Baltic Sea Research (IOW), Seestr. 15, D-18119 Warnemünde, Germany
  • 3Marine Geochemistry, University of Greifswald, Friedrich-Ludwig-Jahn Str. 17a, D-17489 Greifswald, Germany
  • 4Department of Maritime Systems, Interdisciplinary Faculty, University of Rostock, Albert.Einstein-Straße 21, D-18059 Rostock, Germany
  • 5Institute of Coastal Research, Helmholtz Zentrum Geesthacht (HZG), Max-Planck.Str. 1, D-21502 Geesthacht, Germany

Abstract. The coastal ocean is strongly affected by ocean acidification because it is shallow and has a low volume. Earlier observations of dissolved inorganic carbon (DIC) and total alkalinity (TA) in the southern part of the North Sea and the German Bight, a Northwest-European shelf sea, have revealed lower acidification effects than expected. It has been assumed that anaerobic degradation and subsequent TA release in the adjacent tidal areas (Wadden Sea) in summer time is responsible for this phenomenon. In this study the exchange rates of TA and DIC between the Wadden Sea and the North Sea and the consequences for the carbonate system in the German Bight are estimated using a 3-D ecosystem model. Observed TA and DIC sources in the Wadden Sea were considered as boundary conditions. This procedure is based on the dynamic behaviour of the Wadden Sea as an area of effective production and decomposition of organic material. In addition, modelled tidal water mass exchange was used to transport material between the open North Sea and the Wadden Sea. In the model, 39 Gmol TA yr−1 were exported from the Wadden Sea into the North Sea, which is lower than a previous estimate, but within a comparable range. Furthermore, the interannual variabilities of TA and DIC concentrations, which were mainly driven by hydrodynamic conditions, were examined for the years 2001–2009. Variability in the carbonate system of the German Bight is related to weather in that the occurrence of weak meteorological blocking situations leads to enhanced accumulation of TA there. The results suggest that the Wadden Sea is an important driver of the carbonate system variability in the southern North Sea. According to the model results, on average 63 % of all TA mass changes in the German Bight were caused by net transport, 25 % by Wadden Sea export, 9 % were caused by the internal production of TA and 3 % caused by effective TA river loads (i.e. river load including freshwater dilution). The ratio of exported TA and DIC reflects the dominant underlying biogeochemical processes in the different Wadden Sea areas. Aerobic degradation of organic matter plays a key role in the North Frisian Wadden Sea during all seasons of the year. In the East Frisian Wadden Sea anaerobic degradation of organic matter dominated.

Fabian Schwichtenberg et al.

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Fabian Schwichtenberg et al.

Fabian Schwichtenberg et al.

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Short summary
Ocean acidification has a range of potentially harmful consequences for marine organisms. It's related to Total Alkalinity (TA) mainly produced in oxygen-poor situations like sediments in tidal flats. TA reduces the sensitivity of a water body to acidification. The decomposition of organic material and subsequent TA release in the tidal areas of the North Sea (Wadden Sea) is responsible for reduced acidification in the southern North Sea. This is shown with the results of an ecosystem model.
Ocean acidification has a range of potentially harmful consequences for marine organisms. It's...
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