Long Term Data Series on Mediterranean Sea Temperature, Nutrients and Hydrology Changes

The Mediterranean is a deep semi enclosed sea, under a continental climate. Its surface water balance is negative (evaporation losses being greater than precipitation) and water dynamics are controlled by winter dense water formation and by two shallows sills at Gibraltar and Sicily Straits. Consequently, the Algero- Provencal Basin (Western Mediterranean) is filled from 500m depth to the bottom, at more than 2800m, by homogeneous deep water. Its physical characteristics (temperature, salinity) are linked to the heat and water exchanges with the atmosphere and the Atlantic Ocean. Heat exchange with the Atlantic being small, the temperature depends mainly from the heat exchanges through its surface, i.e., from the local climate coupled with the northern hemisphere atmospheric circulation. Salinity depends on exchanges with the Atlantic and on evaporation, precipitation and river runoff. Similarly, the geochemical state of the Mediterranean Sea depends on exchanges with the Atlantic and on atmospheric and terrestrial supplies which are linked to natural and mostly anthropic inputs, issuing from more than 200 millions’ inhabitants who live on the watershed. Unlike the open ocean, for which the deep water response time to perturbations is of the order of 1000 years, the residence time of the western deep water is about 15 years, as a result of intensive horizontal and vertical circulation. Consequently, the Mediterranean response to climatic or environmental changing trends is perceptible in a few years.