30 Years of Repeat Hydrography in the Mediterranean

The Mediterranean Sea is a semi-enclosed Sea characterized by high salinities, temperatures and densities. The net evaporation exceeds the precipitation that, coupled to net heat-loss, drives an anti-estuarine, shallow overturning circulation through the Strait of Gibraltar that communicates directly with the Atlantic Ocean. The Mediterranean Sea also has an active deep water overturning circulation with one cell in each main basin. It is surrounded by populated areas and is thus sensitive to anthropogenic forcing. In a biogeochemical sense the Mediterranean Sea is characterized by very low nutrient and high oxygen concentrations. The high temperature and alkalinity coupled with the well ventilated waters make the Mediterranean Sea an area with very high average anthropogenic CO₂ (C_ant) concentration, so that the basin acts as a globally significant C_ant sink despite its low volume. Several dramatic changes in the oceanographic and biogeochemical conditions have been observed during the past several decades, emphasising the need to better monitor and understand the changing conditions and their drivers.

Although no Mediterranean section was conducted within the WOCE program, several full depth hydrogeochemical cruises has been performed in the Mediterranean Sea during the past several decades, although mostly not covering the whole Mediterranean. During 2011 three oceanographic cruises were conducted in a coordinated fashion in order to produce base-line data of important physical and biogeochemical parameters that can be compared to historic data and be used as reference for future observational campaigns. Since then a zonal section through the Med has been adopted by the international GO-SHIP program to be regularly sampled on a sub-decadal basis. This contribution shows results on major changes in Mediterranean oceanographic conditions during the past 3 decades.