Enhanced ocean carbon storage from anaerobic alkalinity generation in coastal sediments

Abstract

The coastal ocean constitutes the crucial link between land, the open ocean and the atmosphere. Furthermore, its shallow water column permits close interactions between the sedimentary and atmospheric compartments, which otherwise are decoupled at short time scales (<1000 yr) in the open oceans. Despite the prominent role of the coastal oceans in absorbing atmospheric CO sub(2) 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 alkalinity (A sub(T)) and increases the CO sub(2) buffer capacity of seawater. At both the basin wide and annual scales anaerobic A sub(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 CO sub(2) uptake. At the global scale, anaerobic A sub(T) generation could be accountable for as much as 60% of the uptake of CO sub(2) in shelf and marginal seas, making this process, the anaerobic pump, a key player in the biological carbon pump. Under future high CO sub(2) conditions oceanic CO sub(2) storage via the anaerobic pump may even gain further relevance because of stimulated ocean productivity.