Variable export fluxes and efficiencies for calcite, opal, and organic carbon in the Atlantic Ocean: A ballast effect in action?

Latitudinal variability in export fluxes and efficiencies (ThE) of calcite, opal, and particulate organic carbon (POC) were examined during a basin-scale Atlantic Ocean cruise. A clear relationship between integrated euphotic zone POC and calcite export combined with similarities in average ThE for calcite (0.26), opal (0.31), and POC (0.29) implies a potential association between biomineral and POC export. However, such similarity conceals substantial uncorrelated variability when ThE values are compared on regional scales, with ThE of POC often being much higher than that of calcite or opal. High-euphotic zone ThE for POC (0.3-0.4) relative to that found in deep sea sediment traps (<0.05) suggests that considerable remineralization. occurs below the euphotic zone. We suggest (1) that regional variability in the mechanisms by which biominerals and POC become associated are more important in determining the efficient export of organic carbon than that of ballast materials; and (2) that, because of the preferential remineralization of POC relative to calcite/opal dissolution during subeuphotic processes, the potential for effective ballasting increases with depth in the water column.