1GEOMAR Helmholtz Centre for Ocean Research Kiel, Department of Chemical Oceanography, Düsternbrooker Weg 20, 24105 Kiel, Germany
2ZMAW, Institut für Meereskunde, University of Hamburg, Bundesstraße 53, 20146 Hamburg, Germany
3CNR – ISMAR, Institute for Marine Science, Arsenale – Tesa 104 Castello 2737/F, 30122 Venezia, Italy
4OGS – Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Borgo Grotta Gigante 42/c, 34018 Sgonico (Trieste), Italy
5IEO, Instituto Español de Oceanografía, Centro de A Coruña, Apdo. 130, 15001 A Coruña, Spain
Abstract. The Mediterranean Sea is a semi-enclosed sea characterized by high salinities, temperatures and densities. The net evaporation exceeds the precipitation, driving an anti-estuarine circulation through the Strait of Gibraltar, contributing to very low nutrient concentrations. The Mediterranean Sea has an active overturning circulation, one shallow cell that communicates directly with the Atlantic Ocean, and two deep overturning cells, one in each of the two main basins. It is surrounded by populated areas and is thus sensitive to anthropogenic forcing. Several dramatic changes in the oceanographic and biogeochemical conditions have been observed during the past several decades, emphasizing the need to better monitor and understand the changing conditions and their drivers. During 2011 three oceanographic cruises were conducted in a coordinated fashion in order to produce baseline data of important physical and biogeochemical parameters that can be compared to historic data and be used as reference for future observational campaigns. In this article we provide information on the Mediterranean Sea oceanographic situation, and present a short review that will serve as background information for the special issue in Ocean Science on "Physical, chemical and biological oceanography of the Mediterranean Sea". An important contribution of this article is the set of figures showing the large-scale distributions of physical and chemical properties along the full length of the Mediterranean Sea.