Ocean margins as a significant source of organic matter to the deep open ocean

Abstract

Continental shelves and slopes comprise less than 20% of the world ocean area, yet they are proposed to be quantitatively important sources of the organic matter that fuels respiration in the open ocean's interior1,2. At least certain regions of the coastal ocean produce more organic carbon than they respire3, suggesting that some fraction of this non-respired, unburied organic carbon is available for export from the coastal to the open ocean4. Previous studies of carbon fluxes in ocean margins1,5,6 have not considered the potential roles of dissolved organic carbon (DOC) and suspended particulate organic carbon (POCsusp), even though both pools are quantitatively far larger than sinking POC. Here we report natural radiocarbon (14C) abundance measurements that reveal continental slope and rise waters to contain both DOC and POCsusp that are concurrently older and in higher concentrations than DOC and POCsusp from the adjacent North Atlantic and North Pacific central gyres. Mass-balance calculations suggest that DOC and POCsusp inputs from ocean margins to the open ocean interior may be more than an order of magnitude greater than inputs of recently produced organic carbon derived from the surface ocean. Inputs from ocean margins may thus be one of the factors contributing to the old apparent age of organic carbon observed in the deep North Atlantic and Pacific central gyres7,8,9.