Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 6 2 2009 10.5194/bg-6-267-2009 http://www.biogeosciences.net/6/267/2009/ http://www.biogeosciences.net/6/267/2009/bg-6-267-2009.html http://www.biogeosciences.net/6/267/2009/bg-6-267-2009.pdf 267 274 2009-02-25 Enhanced ocean carbon storage from anaerobic alkalinity generation in coastal sediments H. Thomas helmuth.thomas@dal.ca L.-S. Schiettecatte K. Suykens Y. J. M. Koné E. H. Shadwick A. E. F. Prowe Y. Bozec H. J. W. de Baar A. V. Borges Dalhousie University, Dep. of Oceanography, Halifax, Canada Royal Netherlands Institute for Sea Research, Den Burg, Texel, The Netherlands University of Liège, Chemical Oceanography Unit, Liège, Belgium Leibniz-Institut für Meereswissenschaften, IFM-GEOMAR, Kiel, Germany Station Biologique de Roscoff, UMR 7144 CNRS et UPMC Univ. Paris 6, Equipe Chimie Marine, Roscoff, France The coastal ocean is a crucial link between land, the open ocean and the atmosphere. The shallowness of the water column permits close interactions between the sedimentary, aquatic and atmospheric compartments, which otherwise are decoupled at long time scales (≅ 1000 yr) in the open oceans. Despite the prominent role of the coastal oceans in absorbing atmospheric CO₂ and transferring it into the deep oceans via the continental shelf pump, the underlying mechanisms remain only partly understood. Evaluating observations from the North Sea, a NW European shelf sea, we provide evidence that anaerobic degradation of organic matter, fuelled from land and ocean, generates total alkalinity (A_T) and increases the CO₂ buffer capacity of seawater. At both the basin wide and annual scales anaerobic A_T generation in the North Sea's tidal mud flat area irreversibly facilitates 7–10%, or taking into consideration benthic denitrification in the North Sea, 20–25% of the North Sea's overall CO₂ uptake. 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