Predominance of vertical loss of carbon from surface waters of the equatorial Pacific Ocean

Abstract

The equatorial Pacific Ocean makes a significant contribution to global carbon fluxes through both degassing of CO₂ to the atmosphere and new primary production^1–4; the eastern and central region is the source of most of the 1–2 Pg (10¹⁵ g) of CO² supplied annually to the atmosphere by the equatorial oceans⁵, and new primary production in the region may account for up to 18–56% of this global oceanic value⁶. The fate of carbon fixed by new primary production—whether removed to the deep ocean as sinking particles or retained in surface waters requires critical assessment because of the very different timescales of C removal that each process entails. Here we evaluate the transformations of carbon and nitrogen compounds in the surface waters of the South Equatorial Current of the Pacific Ocean. We calculate that carbon removed from the surface layer by degassing and sinking organic particles accounted for 41% and 53%, respectively, of the total C depletion during boreal autumn, 1992. The net accumulation of organic matter in the surface layer, a precondition for its eventual transport away from the Equator by horizontal advec-tion, accounted for <6% of the drawdown, in substantial disagreement with the values up to 75% estimated from recent studies^7–9.