An analysis of western Mediterranean current meter and historical hydrographic data suggests a direct relation in the seasonal inflows of Levantine Intermediate Water (LIW) through the Strait of Sicily and Atlantic Water (AW) through the Strait of Gibraltar. The analysis indicates that the seasonal extremes of the two inflows are phased 90¿ apart. Thus LIW and AW alternate in accumulating in the western Mediterranean, the minimum LIW volume occurring during February--June and the maximum during July--December, with the extreme AW volumes reversed during these periods. It is suggested that during the period of maximum LIW volume, the ratio of the denser LIW to the lighter AW in the water column increases and, due to the resulting denser water column, the sea level of the western Mediterranean is lowered. The depressed sea level in turn causes an increase in the AW inflow through the Strait of Gibraltar. The seasonal AW inflow changes generated by these events are inferred to be primarily responsible for the year-round variability of the western Mediterranean surface layer circulation. ¿ American Geophysical Union 1990