SHOALING OF THE EASTERN MEDITERRANEAN PYCNOCLINE DUE TO REDUCTION OF EXCESS EVAPORATION: IMPLICATIONS FOR SAPROPEL FORMATION

A simple two-layered model is applied to assess the relation between variations in the depth of the permanent pycnocline and changes in the excess of evaporation over freshwater input, in the eastern Mediterranean. This study is performed to estimate the magnitude of the excess evaporation at times of sapropel formation in the eastern Mediterranean. Pycnocline shoaling, from a depth below the euphotic layer to a depth within that layer at times of sapropel formation, has been inferred from the planktonic foraminiferal record by Rohling and Gieskes (1989). The model suggests that a decrease in the eastern Mediterranean excess evaporation, defined as evaporation minus total freshwater input, by about 8.5 x 10(11) m(3) yr(-1) would suffice to invoke shoaling of the pycnocline to a depth within the euphotic layer. A consideration of the effects exerted by concomitant changes in the thermal balance suggests that the necessary decrease of excess evaporation may even be smaller than the above estimate.