Enhanced ocean carbon storage from anaerobic alkalinity generation in coastal sediments

摘要

The coastal ocean is a crucial link between land, the open ocean andthe atmosphere. The shallowness of the water column permits closeinteractions between the sedimentary, aquatic and atmospheric compartments,which otherwise are decoupled at long time scales (≅ 1000 yr) in theopen oceans. Despite the prominent role of the coastal oceans in absorbingatmospheric CO₂ and transferring it into the deep oceans viathe continental shelf pump, the underlying mechanisms remain only partlyunderstood. Evaluating observations from the North Sea, a NW European shelfsea, 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 thebasin wide and annual scales anaerobic A_T generation in theNorth Sea's tidal mud flat area irreversibly facilitates 7–10%, or takinginto consideration benthic denitrification in the North Sea, 20–25% ofthe North Sea's overall CO₂ uptake. At the global scale,anaerobic A_T generation could be accountable for as much as60% of the uptake of CO₂ in shelf and marginal seas, makingthis process, the anaerobic pump, a key player in the biological carbonpump. Under future high CO₂ conditions oceanicCO₂ storage via the anaerobic pump may even gain furtherrelevance because of stimulated ocean productivity.