Reconciling opposing views on carbon cycling in the coastal ocean: Continental shelves as sinks and near-shore ecosystems as sources of atmospheric CO2

Abstract

Despite their moderately sized surface area, continental marginal seas play a significant role in the biogeochemical cycles of carbon, as they receive huge amounts of upwelled and riverine inputs of carbon and nutrients, sustaining a disproportionate large biological activity compared to their relative surface area. A synthesis of worldwide measurements of the partial pressure of CO2 (pCO2) indicates that most open shelves in the temperate and high-latitude regions are under-saturated with respect to atmospheric CO2 during all seasons, although the low-latitude shelves seem to be over-saturated. Most inner estuaries and near-shore coastal areas on the other hand are over-saturated with respect to atmospheric CO2. The scaling of air–sea CO2 fluxes based on pCO2 measurements and carbon massbalance calculations indicate that the continental shelves absorb atmospheric CO2 ranging between 0.33 and 0.36 Pg C yr � 1 that corresponds to an additional sink of 27% to � 30% of the CO2 uptake by the open oceans based on the most recent pCO2 climatology [Takahashi, T., Sutherland, S.C., Wanninkhof, R.,