Ventilation of deep waters in the Adriatic and Ionian Seas following changes in thermohaline circulation of the Eastern Mediterranean

摘要

ABSTRACT: Hydrographic measurements obtained in March–April 2002 indicate a new ventilation of the deep layers in the Adriatic and Ionian Seas, following abrupt changes in the thermohaline circulation of the eastern Mediterranean observed since the beginning of the last decade. The water masses that reside in the Southern Adriatic basin were renewed by open ocean winter convection of water with potential density excess (σ_θ) 29.18 kg m^–3 at depths 600 to 800 m and by a vein of still denser (29.26 kg m^–3) and oxygen-rich (230 to 232 mmol m^–3) water flowing into the southern Adriatic depression (~1200 m), presumably from the north. When compared to 1999, a moderate increase in salinity (~0.05) and a much stronger dissolved oxygen increase (29 mmol m^–3) were found in the bottom layer of the southern Adriatic Sea. The cold, fresh and highly oxygenated water of Adriatic origin, overflowing the Otranto Strait sill (~935 m) with a potential density of 29.24 kg m^–3, was dense enough to sink into the deep Ionian basin. Multiparameter analysis based on the fundamentals of the mixing processes was applied using temperature, salinity, oxygen and nutrient data to investigate the spatial distribution of water masses and to quantify the fractional contributions of distinctive source water types along specific sections running from the Adriatic to the Ionian Sea. The results clearly indicate that the dense water of Adriatic origin, which was recently in contact with the atmosphere, have again replenished the volume of the deep Ionian basin by more than 50%.