Rapid coupling of sinking particle fluxes between surface and deep ocean waters

Abstract

SETTLING particles are thought to be responsible for much of the transport of mass and energy from the upper ocean to the sea floor. Photosynthetic production by phytoplankton is a major source of these particles, either as phytoplankton biomass sinks directly¹or as it is transformed into rapidly sinking forms such as aggregates^2,3 and zooplankton faeces⁴. Because a variety of processes may act on sinking matter, however, it is not known to what extent fluxes of organic matter to the deep sea are coupled to processes at the ocean surface. Some studies have provided evidence for direct coupling^2,5–7, but transformation processes and advection exist which have the potential to modify the transmission of surface signals to the deep sea^8–11. If these mechanisms overwhelm surface production signals, seasonal and annual variations in deep-sea geochemistry and biology would be controlled largely by lateral processes associated with ocean circulation rather than by surface processes. Here we report direct measurements of seasonal variations in upper-ocean primary production concurrent with particle fluxes measured at several depths ranging from the upper to the deep ocean in the Atlantic. We find that the productivity signal can be transferred rapidly to the deep sea by settling particles, yielding close temporal coupling between the surface and deep oceans.