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 CO2 (pCO2) 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 pCO2 decrease sharply from their winter surface values. As part of OMEX I, the late summer distribution of surface water pCO2 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 pCO2 difference (ΔpCO2) measured on these ship surveys was generally in accord with that observed in this area in early to mid-summer of 1981. The greatest CO2 undersaturation (-95 μatm) during our surveys was observed near the west coast of Iceland, with ΔpCO2 increasing to about -60 μatm away from the coast. In shelf waters south of Ireland, the pCO2 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 CO2 concentration. Because of the variation of wind speed, the synoptic distribution of air-sea CO2 flux, derived from the transfer velocity and ΔpCO2, does not resemble the distribution of ΔpCO2 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 CO2, to a level of about 10-14mol m-2a-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 pCO2 undersaturation