Abstract
Estimates of evaporation (E) over the North Atlantic Ocean by Bunker have been combined with estimates of precipitation (P) by Dorman and Bourke to produce new annual and seasonal maps of E–P and surface density flux. Although uncertainties about precipitation algorithms and exchange coefficients still presist, it is felt that the high spatial resolution of these data set permits an estimate of E–P that is a significant improvement over previous work. The maps of E–P show considerably more detail than earlier maps, including a previously uncharted minimum with a northeast to southwest trend across the subtropical gyre. The two regions of maximal E–P display a close connection with continental air flows off Africal and North America, suggesting that the relative narrowness of the North Atlantic contributes to its status as a net evaporation basin. The zonally integrated E–P values are combined with river runoff estimates to obtain the meridional flux of freshwater, which can be compared with fluxes calculated from oceanographic sections.
Maps of the surface density flux are also presented for the annual and seasonal averages. Areas of net density gain by the ocean correspond to formation regions of subpolar mode water at high latitudes, 18°C water south of the Gulf Stream, and salinity maximum water at low latitudes in midgyre. The contributions of heat and salt to the density flux are separately computed. This reveals that the thermal density flux dominates at high and low latitudes whereas the haline density flux is most important in the subtropics, particularly on the eastern side of the basin. These data should facilitate the development of models of the thermohaline circulation, and aid the identification of regional differences in the dominant air–sea interaction processes.
