Partial pressure and air-sea flux of CO2 in the Northeast Atlantic during September 1995

Previous work has shown that during early summer, the partial pressure of C O2 (pCO(2)) in surface waters north of about 45 degreesN in the Atlantic ex hibits widespread undersaturation. In many areas. this follows after a "spr ing bloom" of phytoplankton, at which time, nutrient concentrations and pCO (2) decrease sharply from their winter surface values. As part of OMEX I, t he late summer distribution of surface water pCO(2) was surveyed in the nor theastern Atlantic on cruises of R/V Poseidon and R/V Belgica in 1995. The pattern of the surface distribution of the sea-air pCO(2) difference (Delta pCO(2)) measured on these ship surveys was generally iri accord with that observed in this area in early to mid-summer of 1981. The greatest CO2 unde rsaturation (-95 mu atm) during our surveys was observed near the west coas t of Iceland, with Delta pCO(2) increasing to about -60 mu atm away from th e coast. In shelf waters south of Ireland, the pCO(2) was relatively higher than in surface waters of the open ocean adjacent to the Celtic Shelf marg in, but the Celtic Shelf waters were still undersaturated relative to the a tmospheric CO2 concentration. Because of the variation of wind speed, the s ynoptic distribution of air-sea CO2 flux, derived from the transfer velocit y and Delta pCO(2), does not resemble the distribution of Delta pCO(2) itse lf. The sharp increase in wind speed at about 53 degreesN, 20 degreesW duri ng the R/V Poseidon survey produces an order of magnitude rise in the estim ated air-sea flux of CO2, to a level of about 10-14 mol m(-2) a(-1). The ov erall synoptic picture appears to be one of moving centers of higher air-se a fluxes that occur where storms pass over regions of surface water pCO(2) undersaturation. (C) 2001 Elsevier Science Ltd. All rights reserved.