Coastal metabolism and the oceanic organic carbon balance

TLDR

Net organic metabolism in the coastal ocean, the difference between primary production and respiration, may be a significant term in the oceanic carbon budget, and its historical change determines the coastal ocean's importance relative to anthropogenic perturbations of the global carbon cycle. By considering long‑term river loading, organic burial, chemical reactivity of land‑derived organic matter, and community metabolism, the authors estimate coastal oxidation at ~7×10¹² mol C yr⁻¹, with bays and estuaries especially important due to altered land inputs. The ocean is a net source of CO₂, oxidizing ~16×10¹² mol C yr⁻¹, with the coastal zone contributing about 30 % of this oxidation.

Abstract

Net organic metabolism (that is, the difference between primary production and respiration of organic matter) in the coastal ocean may be a significant term in the oceanic carbon budget. Historical change in the rate of this net metabolism determines the importance of the coastal ocean relative to anthropogenic perturbations of the global carbon cycle. Consideration of long‐term rates of river loading of organic carbon, organic burial, chemical reactivity of land‐derived organic matter, and rates of community metabolism in the coastal zone leads us to estimate that the coastal zone oxidizes about 7 × 10 12 moles C/yr. The open ocean is apparently also a site of net organic oxidation (∼16 × 10 12 moles C/yr). Thus organic metabolism in the ocean appears to be a source of CO 2 release to the atmosphere rather than being a sink for atmospheric carbon dioxide. The small area of the coastal ocean accounts for about 30% of the net oceanic oxidation. Oxidation in the coastal zone (especially in bays and estuaries) takes on particular importance, because the input rate is likely to have been altered substantially by human activities on land.