Response of the Mediterranean Sea thermohaline circulation to observed changes in the winter wind stress field in the period 1980–1993

Abstract

This paper seeks to model changes in deep water production in the eastern Mediterranean induced by changes in winter wind stress. An analysis of individual monthly wind stress fields over the Mediterranean for 1980–1993 from the SOC flux data set shows that an intensification of the winter mean (mainly January) wind stress over the Aegean Sea and Levantine basin occurred in the latter half of this period. A weakening of the Mistral occurred at the same time. Two monthly wind stress climatologies were created using the 1980–1987 and 1988–1993 periods, and these were used to force an ocean general circulation model of the Mediterranean, with climatological surface T, S relaxation. The Levantine intermediate water (LIW) dispersal path in the Ionian is altered in the 1988–1993 experiment with no pathway to the Adriatic and, consequently, greatly reduced exchange at Otranto and a collapse in Adriatic deep water formation. In contrast, there is an increased exchange of LIW at the Cretan arc straits and enhanced Aegean deep water production in the 1988–1993 experiment. Much more Aegean water exits into the Levantine and Ionian basins as is shown by an east‐west cross section south of Crete, along a similar path to the Meteor cruise in 1995. Changes in air‐sea fluxes are diagnosed from the model showing a small increase in wintertime cooling over the Aegean and reduced cooling over the Adriatic after 1987. While the changes in air‐sea fluxes are probably underrepresented by this simulation, the large changes induced by the wind forcing suggest this could be a mechanism in the altered thermohaline state of the eastern Mediterranean since 1987.