The paper provides a basin-scale assessment of the spatiotemporal distribution ofalkalinity in the Mediterranean Sea. The assessment is made by integratingthe available observations into a 3-D transport–biogeochemical model.The results indicate the presence of complex spatial patterns: a markedwest-to-east surface gradient of alkalinity is coupled to secondary negativegradients: (1) from marginal seas (Adriatic and Aegean Sea) to the easternMediterranean Sea and (2) from north to south in the western region. Thewest–east gradient is related to the mixing of Atlantic water enteringfrom the Strait of Gibraltar with the high-alkaline water of the easternsub-basins, which is correlated to the positive surface flux of evaporationminus precipitation. The north-to-south gradients are related to theterrestrial input and to the input of the Black Sea water through the Dardanelles.In the surface layers, alkalinity has a relevant seasonal cycle (up to 40 μmol kg−1) that is driven by physical processes (seasonal cycleof evaporation and vertical mixing) and, to a minor extent, bybiological processes. A comparison of alkalinity vs. salinity indicates thatdifferent regions present different relationships: in regions of freshwaterinfluence, the two quantities are negatively correlated due to riverinealkalinity input, whereas they are positively correlated in open sea areasof the Mediterranean Sea.
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