PREDOMINANCE OF VERTICAL LOSS OF CARBON FROM SURFACE WATERS OF THE EQUATORIAL PACIFIC-OCEAN

The equatorial Pacific Ocean makes a significant contribution to globa l carbon fluxes through both degassing of CO2 to the atmosphere and ne w primary production(1-4); the eastern and central region is the sourc e of most of the 1-2 Pg (10(15) g) of CO2 supplied annually to the atm osphere by the equatorial oceans(5), and new primary production in the region may account for up to 18-56% of this global oceanic value(6). The fate of carbon fixed by new primary production-whether removed to the deep ocean as sinking particles or retained in surface waters requ ires critical assessment because of the very different timescales of C removal that each process entails. Here we evaluate the transformatio ns of carbon and nitrogen compounds in the surface waters of the South Equatorial Current of the Pacific Ocean. We calculate that carbon rem oved from the surface layer by degassing and sinking organic particles accounted for 41% and 53%, respectively, of the total C depletion dur ing boreal autumn, 1992. The net accumulation of organic matter in the surface layer, a precondition for its eventual transport away from th e Equator by horizontal advection, accounted for <6% of the drawdown, in substantial disagreement with the values up to 75% estimated from r ecent studies(7-9).