Alkalinity and salinity are linearly correlated in the waters of the most western part of the Mediterranean Sea. Nevertheles, the specific alkalinity of the saltier Mediterranean waters is higher than that of the less saline water of Atlantic origin. This may be explained by alkalinity input from rivers and the Black Sea. In the hypothesis of a steady state, the relationship between alkalinity and salinity permits calculation of the net flux of alkalinity between the Mediterranean Sea and the Atlantic Ocean, provided the water budget of the Mediterranean is known. The sources (rivers and the Black Sea) and sinks (seafloor) or alkalinity in the Mediterranean balance the net alkalinity transport into the Atlantic, if the water deficit of the Mediterranean is 2.2¿1012 m3 yr-1 or 88 cm yr-1 per unit area. The budget of carbon in the Mediterranean Sea is more difficult to assess as the sources and sinks are numerous and not well-documented. There is particularly a lack of data on the seasonal variations in the inorganic and organic carbon concentrations in the region of the strait of Gibraltar and on the partial pressure of CO2 in surface water of the Mediterranean Sea. It appears nevertheless that there is an important flux of inorganic carbon from the Mediterranean to the Atlantic due to the supply of carbon by the rivers and the Black Sea and to the transformation of 40% of the organic carbon entering the Mediterranean in inorganic carbon. Moreover, the Mediterranean is likely a sink for the atmospheric carbon.