Particulate fluxes of carbonate and organic carbon in the ocean. Is the marine biological activity working as a sink of the atmospheric carbon?

The particulate fluxes of carbonate carbon and organic carbon observed in various oceans have been summarized in this paper and discussed with special reference to the fate of the atmospheric carbon dioxide. The organic carbon fluxes, which act as a sink of atmospheric carbon dioxide, are generally larger than the carbonate carbon fluxes working as a source, but are comparable in the deep subtropical oceans. The areal and vertical variations of the carbonate carbon fluxes are much smaller than those of the organic carbon fluxes, indicating that organisms producing carbonate particles exist rather evenly in the world ocean and that a substantial part of carbonate produced is transported to the ocean bottom. The particulate fluxes are much larger in the coastal and hemipelagic seas. Although the productivity of shallow seas holds a key role in the fate of anthropogenic carbon, the marine biota may not be a large sink when longer time scales are considered. The carbonate carbon fluxes in the productive northern Pacific are larger in the northeast Pacific than in the northwest Pacific, reflecting a difference in the ecosystems. This suggests that the eutrophication of marine environments may not necessarily act as a sink for the atmospheric carbon dioxide.