| Summary: | Previous work has shown that during early summer, the partial pressure of CO 2 (pCO 2 ) in surface waters north of about 45°N in the Atlantic exhibits widespread undersaturation. In many areas. this follows after a "spring bloom" of phytoplankton, at which time, nutrient concentrations and pCO 2 decrease sharply from their winter surface values. As part of OMEX I, the late summer distribution of surface water pCO 2 was surveyed in the northeastern 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 in accord with that observed in this area in early to mid-summer of 1981. The greatest CO 2 undersaturation (-95 µatm) during our surveys was observed near the west coast of Iceland, with Delta pCO 2 increasing to about -60 µatm away from the 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 margin, but the Celtic Shelf waters were still undersaturated relative to the atmospheric CO 2 concentration. Because of the variation of wind speed, the synoptic distribution of air-sea CO 2 flux, derived from the transfer velocity and Delta pCO 2 , does not resemble the distribution of Delta pCO 2 itself. The sharp increase in wind speed at about 53°N, 20°W during the R/V Poseidon survey produces an order of magnitude rise in the estimated air-sea flux of CO 2 , to a level of about 10-14 mol m -2 a -1 . The overall synoptic picture appears to be one of moving centers of higher air-sea fluxes that occur where storms pass over regions of surface water pCO 2 undersaturation.
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