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 particu larly to freshwater budget across its surface. In the sediment of the easte rn basin, the sapropel layers are signatures of variations in hydrology and climate that have occurred over the last half million years. They may be u sed to investigate the probable evolutions following global climatic change , and particularly the sensitivity of marine dynamics to freshwater input v ariations. At the present time, in the water column of the eastern and west ern basins, there are changes in hydrology originating in evolutions in hea t and water budgets across the sea surface. With respect to the water budge t of the Mediterranean, some evolutions have occurred as a result of the an thropogenic use of freshwater, and consequently, environmental driving forc es must also be considered alongside climatic factors. Marine variations ma y be used as constraints for the quantification of probable evolutions in e xternal driving forces at the scale of a whole basin. As an example, the pr eviously 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 budge ts, reaching 0.1 m yr(-1) and 1.5 W m(-2), respectively, in 1995 over the M editerranean. (C) 1999 Elsevier Science B.V. All rights reserved.