A study of water mass transformation in the Mediterranean Sea: analysis of climatological data and a simple three-box model

Abstract

Upper bounds are estimated for the rates of water mass formation in different regions of the Mediterranean Sea by calculating the monthly climatological air-sea fluxes of heat and fresh water as a function of the surface density. It is found that a yearly averaged flux of about 4 Sverdrup (Sv) of surface water whose density is in the intermediate density range 26.2> σ>28.7 is transformed by air-sea fluxes to greater densities, and about 2 Sverdrups are transformed to lesser densities. Part (possibly a small part) of the water transformed into higher density ranges sinks and forms the intermediate and deep water masses. The calculation therefore gives an estimated maximal bound of about 4 Sverdrup for the yearly averaged water mass formation in the Mediterranean. Similar calculations for the Eastern Mediterranean alone give bounds of Levantine Intermediate Water formation (1–1.5 Sv), as well as formation in the Adriatic Sea (1–1.5 Sv). A simple model using three variable-volume boxes to represent a marginal sea under seasonal forcing is used to support the data analysis. The model and the data analysis demonstrate the crucial role of mixing and of the seasonal cycle in shaping the water mass transformation in the Mediterranean Sea.