Nutrient distribution in the eastern Mediterranean before and after the transient event

The Eastern Mediterranean Transient (EMT) event in the 1990's produced a new deep water mass, the Cretan Sea Outflow Water (CSOW), that was warmer, saltier, more oxygenated and with lower nutrient concentrations than the Adriatic Deep Water (ADW). The CSOW uplifted the older ADW and changed the distribution of the physical and chemical parameters in the Eastern Mediterranean creating a mid-depth layer with minimum temperature and salinity across the basin. It also created a minimum oxygen (MinOx) and maximum nutrients (MaxNut) layer in the Levantine basin and Cretan sea. The CSOW, first noticed in the vicinity of Crete near its source, propagated initially towards the western Ionian and later towards the Levantine basin, uplifting the MinOx/MaxNut layer from 1250 m to 950 m and 750 m in the Levantine and Ionian basin, respectively, between 1995 and 2001. This layer was narrower and more eroded in the Ionian and more emphasized the Levantine. The main influence of the EMT event was on the intermediate and deep water levels. As the uplifting and erosion of the ADW continued with the CSOW evolution in the basin, water richer in nutrients was brought closer to the photic zone and within reach of microbial communities, in particular in the Levantine basin. To date, chlorophyll-a (chl-a) concentration did not increase and remained similar to the pre-EMT in most of the Eastern Mediterranean, except for the Northwest Ionian. It may be that the utilization passes rapidly through the phytoplankton not changing the chl-a concentration but affecting at higher trophic levels. However, if nutrient supply continues to increase, either by the continuing changes during the relaxation of the EMT event or by other processes, such as increased atmospheric deposition or transport from the coast, an environmental threshold may be reached and induce changes in the phytoplankton communities.