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  Interannual sedimentary effluxes of alkalinity in the southern North Sea: Model results compared with summer observations

Pätsch, J., Kühn, W., & Six, K. D. (2018). Interannual sedimentary effluxes of alkalinity in the southern North Sea: Model results compared with summer observations. Biogeosciences, 15(Spec. Iss.: Progress in quantifying ocean biogeochemistry – in honour of Ernst Maier-Reimer), 3293-3309. doi:10.5194/bg-15-3293-2018.

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Pätsch, Johannes1, Author           
Kühn , W.2, Author
Six, Katharina D.1, 3, Author           
Affiliations:
1B 3 - Marine and Coastal Systems, Research Area B: Climate Manifestations and Impacts, The CliSAP Cluster of Excellence, External Organizations, ou_1863483              
2Theoretical Oceanography, Institute of Oceanography, University of Hamburg, Hamburg, Germany, ou_persistent22              
3Ocean Biogeochemistry, The Ocean in the Earth System, MPI for Meteorology, Max Planck Society, ou_913556              

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 Abstract: For the sediments of the central and southern North Sea different sources of alkalinity generation are quantified by a regional modelling system for the period 2000-2014. For this purpose a formerly global ocean sediment model coupled with a pelagic ecosystem model is adapted to shelf sea dynamics, where much larger turnover rates than in the open and deep ocean occur. To track alkalinity changes due to different nitrogen-related processes, the open ocean sediment model was extended by the state variables particulate organic nitrogen (PON) and ammonium. Directly measured alkalinity fluxes and those derived from Ra isotope flux observation from the sediment into the pelagic are reproduced by the model system, but calcite building and calcite dissolution are underestimated. Both fluxes cancel out in terms of alkalinity generation and consumption. Other simulated processes altering alkalinity in the sediment, like net sulfate reduction, denitrification, nitrification, and aerobic degradation, are quantified and compare well with corresponding fluxes derived from observations. Most of these fluxes exhibit a strong positive gradient from the open North Sea to the coast, where large rivers drain nutrients and organic matter. Atmospheric nitrogen deposition also shows a positive gradient from the open sea towards land and supports alkalinity generation in the sediments. An additional source of spatial variability is introduced by the use of a 3-D heterogenous porosity field. Due to realistic porosity variations (0.3-0.5) the alkalinity fluxes vary by about 4 . The strongest impact on interannual variations of alkalinity fluxes is exhibited by the temporal varying nitrogen inputs from large rivers directly governing the nitrate concentrations in the coastal bottom water, thus providing nitrate necessary for benthic denitrification. Over the time investigated the alkalinity effluxes decrease due to the decrease in the nitrogen supply by the rivers. © Author(s) 2018.

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Language(s): eng - English
 Dates: 20182018-06-042018-06-04
 Publication Status: Issued
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 Rev. Type: Peer
 Identifiers: DOI: 10.5194/bg-15-3293-2018
BibTex Citekey: Pätsch20183293
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Title: Biogeosciences
Source Genre: Journal
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Publ. Info: Copernicus GmbH
Pages: - Volume / Issue: 15 (Spec. Iss.: Progress in quantifying ocean biogeochemistry – in honour of Ernst Maier-Reimer) Sequence Number: - Start / End Page: 3293 - 3309 Identifier: ISSN: 17264170