Articles | Volume 13, issue 3
Biogeosciences, 13, 841–863, 2016
Biogeosciences, 13, 841–863, 2016

Research article 12 Feb 2016

Research article | 12 Feb 2016

The impact of sedimentary alkalinity release on the water column CO2 system in the North Sea

H. Brenner1, U. Braeckman2, M. Le Guitton1, and F. J. R. Meysman1,3 H. Brenner et al.
  • 1Department of Ecosystem Studies, Royal Netherlands Institute for Sea Research (NIOZ), Korringaweg 7, 4401 NT Yerseke, the Netherlands
  • 2Marine Biology Research Group, Ghent University, Krijgslaan 281 S8, 9000 Ghent, Belgium
  • 3Department of Analytical, Environmental and Geochemistry, Free University of Brussels (VUB), Pleinlaan 2, 1050 Brussels, Belgium

Abstract. It has been previously proposed that alkalinity release from sediments can play an important role in the carbonate dynamics on continental shelves, lowering the pCO2 of seawater and hence increasing the CO2 uptake from the atmosphere. To test this hypothesis, sedimentary alkalinity generation was quantified within cohesive and permeable sediments across the North Sea during two cruises in September 2011 (basin-wide) and June 2012 (Dutch coastal zone). Benthic fluxes of oxygen (O2), alkalinity (AT) and dissolved inorganic carbon (DIC) were determined using shipboard closed sediment incubations. Our results show that sediments can form an important source of alkalinity for the overlying water, particularly in the shallow southern North Sea, where high AT and DIC fluxes were recorded in near-shore sediments of the Belgian, Dutch and German coastal zone. In contrast, fluxes of AT and DIC are substantially lower in the deeper, seasonally stratified, northern part of the North Sea. Based on the data collected, we performed a model analysis to constrain the main pathways of alkalinity generation in the sediment, and to quantify how sedimentary alkalinity drives atmospheric CO2 uptake in the southern North Sea. Overall, our results show that sedimentary alkalinity generation should be regarded as a key component in the CO2 dynamics of shallow coastal systems.

Short summary
Alkalinity released from sediments of the southern North Sea can play an important role in the carbon cycle of the North Sea by lowering the pCO2 of the seawater and thus increasing the CO2 flux between the atmosphere and the water. However, not every single mole alkalinity generated in sediments leads to an additional CO2 uptake, as certain reactions in the water column can negate the respective alkalinity release.
Final-revised paper