Major advances in the oceanography of the southern Aegean Sea–Cretan Straits system (eastern Mediterranean)

Abstract

The CEC/MAST-MTP PELAGOS Project, which was conducted in 1994 and 1995, found a new dynamic hydrological regime in the Cretan Sea–Cretan Straits region that is interacting with and affecting the whole basin of the Eastern Mediterranean. In the Cretan Sea, the upper thermocline general circulation shows no significant seasonal signal, but the circulation patterns observed were significantly different from those observed in 1986–87, suggesting that there is substantial interannual variability. There was a persistent outflow of Cretan Deep Water (CDW) with an annual mean flow of 0.6 Sv, which was making a substantial contribution to the formation of a new warmer, saltier and denser Deep Water of the Eastern Mediterranean, that was displacing upwards the Eastern Mediterranean Deep Water (EMDW) of Adriatic origin. Thus, the Cretan Sea is the unique source of a new type of the EMDW. There is an inflow of Transition Mediterranean Water (TMW) of low salinity, temperature and oxygen, but rich in nutrients into the South Aegean Sea (Cretan Sea) at intermediate depths (200–600 m) from the open sea areas of the Eastern Mediterranean, which is drastically changing the chemical conditions of the region. Biomass concentrations, primary production rates, the chemical constituents of the suspended particulate matter and the total mass fluxes of settling particles confirm that the South Aegean is one of the most oligotrophic regions of the world. Dissolved element concentrations are comparable to those reported for other straits of the Mediterranean. Particulate Fe and Mn occur in unusually high concentrations, probably originating from hydrothermal sources in the South Aegean Sea. It is expected that the nutrient enrichment of the intermediate layers in the Cretan Sea will influence the extremely oligotrophic character of the South Aegean and is having a direct effect on the biology of the region.