EXPERIMENTAL-DETERMINATION OF THE ORGANIC-CARBON FLUX FROM OPEN-OCEANSURFACE WATERS

The flux of biologically produced organic carbon from the euphotic zon e of the ocean to the deep waters below-the 'biological organic carbon pump'-is one of the main controls on the carbon dioxide partial press ure in the atmosphere(1). Accurate determination of this flux is there fore critically important for understanding the global carbon cycle an d its response to climate change. Our goal is to assess how accurately the biological organic carbon pump can be determined at a single loca tion and to constrain estimates of the global value. As there are no s tandards against which such environmental fluxes can be measured, we a ssess accuracy by comparing results from three independent experimenta l approaches for measuring the net annual export of organic carbon fro m the euphotic zone in the subtropical North Pacific Ocean near Hawaii . Mass balances of dissolved oxygen, inorganic carbon and organic carb on yield estimates of the organic carbon export flux of 2.7 +/- 1.7, 1 .6 +/- 0.9 and 2.0 +/- 0.9 mol C m(-2)yr(-1), respectively, These thre e estimates are not significantly different, and establish the present analytically attainable accuracy at this location to be about +/-50%. If 2.0 mol C m(-2)yr(-1) is typical of the organic carbon export flux in the subtropical ocean, then this vast region, often considered to be a biological desert, may be responsible for up to half of the globa l-ocean biological organic carbon pump.