AN ASSESSMENT OF THE ROLE OF THE NORTH-ATLANTIC AS A CO2 SINK

A numerical interpolation scheme based upon the lateral diffusive and advective transport of ocean surface waters has been developed to inte rpolate measurements made in irregular time and space over the oceans. This has been applied to about 2700 surface ocean pCO(2) measurements observed during the period 1972-1992 in the North Atlantic to give th e distribution of sea-air pCO(2) difference (Delta pCO(2)) over the At lantic. Although the atmospheric CO2 concentration has increased by ab out 28 ppm over this period, the pCO(2) values in the surface waters o f subarctic regions have increased little because they are dictated pr imarily by the properties of underlying deep waters through vertical m ixing. Accordingly, Delta pCO(2) values measured north of 50 degrees N have been corrected to the year 1990 using the secular increase of at mospheric CO2. Because the surface water pCO(2) value in temperate wat ers tracks the secular increase in atmospheric CO2 with a time lag of about two years, no correction was applied to the warm water Delta pCO (2) data. It has been assumed that seasonal variations are the same fo r each year. The net CO2 flux across the sea surface has been computed over a 4 degrees latitude x 5 degrees longitude grid using the mean m onthly Delta pCO(2) values and the gas transfer coefficients estimated using the mean monthly wind speed. It has been found that the areas o f the high latitude North Atlantic and the adjacent seas north of 42 d egrees N are net CO2 sinks of 0.2 to 0.5 Gt C a(-1). The total sink fl ux of CO2 over the temperate North Atlantic areas between 18 degrees N and 420 N is balanced approximately by the source flux over the tropi cal Atlantic between 18 degrees N and 18 degrees S.