Seasonal heat and freshwater budgets of the upper ocean in the North‐east Atlantic

Abstract

AbstractHeat‐ and freshwater‐content changes were calculated from two repeated sections at 48°N, 18°W and 48°N, 26°W, surveyed during the Vivaldi cruise of the research ship RRS Charles Darwin in May 1991. Best estimates of the air‐sea heat‐fluxes agreed within error with the observed heat‐content changes, suggesting that diabatic forcing dominated the heat budget. This was confirmed by a numerical model which showed that Ekman and geostrophic advection and eddy diffusion together contributed less than 20 W m−2 to the heat budget.However, the model also showed that, near the oceanic polar front under westerly winds, Ekman advection of cold, fresh water southwards over the front can cause ‐40 W m−2 and 4 mm d−1 heat‐ and freshwater‐content changes in the upper 53 m, compared to air‐sea fluxes of typically 67 W m−2 and less than 1 mm d−1. the Ekman advection contributed little to the model's density‐budget as the advective cooling and freshening had opposing effects. However, an air‐sea interaction model showed that the advective surface‐cooling may be reduced because it triggers an extra air‐sea heat flux and the remaining advective freshening then makes an important contribution to the density budget.