Functioning of the Mediterranean Sea: past and present changes related to freshwater input and climate changes

Mediterranean functioning is linked to continental climate and more particularly to freshwater budget across its surface. In the sediment of the eastern basin, the sapropel layers are signatures of variations in hydrology and climate that have occurred over the last half million years. They may be used to investigate the probable evolutions following global climatic change, and particularly the sensitivity of marine dynamics to freshwater input variations. At the present time, in the water column of the eastern and western basins, there are changes in hydrology originating in evolutions in heat and water budgets across the sea surface. With respect to the water budget of the Mediterranean, some evolutions have occurred as a result of the anthropogenic use of freshwater, and consequently, environmental driving forces must also be considered alongside climatic factors. Marine variations may be used as constraints for the quantification of probable evolutions in external driving forces at the scale of a whole basin. As an example, the previously developed 20-box model provides an explanation for the increasing trends of temperature and salinity observed in the western deep water over the 1960–1996 period by accounting for changes in freshwater and heat budgets, reaching 0.1 m yr−1 and 1.5 W m−2, respectively, in 1995 over the Mediterranean.