On the steric and mass-induced contributions to the annual sea level variations in the Mediterranean Sea

摘要

The sea level variation (SLV total) is the sum of two major contributions: steric and mass-induced. The steric SLV steric is that resulting from the thermal and salinity changes in a given water column. It only involves volume change, hence has no gravitational effect. The mass-induced SLV mass, on the other hand, arises from adding or subtracting water mass to or from the water column and has direct gravitational signature. We examine the closure of the seasonal SLV budget and estimate the relative importance of the two contributions in the Mediterranean Sea as a function of time. We use ocean altimetry data (from TOPEX/Poseidon, Jason 1, ERS, and ENVISAT missions) to estimate SLV total, temperature, and salinity data (from the Estimating the Circulation and Climate of the Ocean ocean model) to estimate SLV steric, and time variable gravity data (from Gravity Recovery and Climate Experiment (GRACE) Project, April 2002 to July 2004) to estimate SLV mass. We find that the annual cycle of SLV total in the Mediterranean is mainly driven by SLV steric but moderately offset by SLV mass. The agreement between the seasonal SLV mass estimations from SLV total – SLV steric and from GRACE is quite remarkable; the annual cycle reaches the maximum value in mid-February, almost half a cycle later than SLV total or SLV steric, which peak by mid-October and mid-September, respectively. Thus, when sea level is rising (falling), the Mediterranean Sea is actually losing (gaining) mass. Furthermore, as SLV mass is balanced by vertical (precipitation minus evaporation, P–E) and horizontal (exchange of water with the Atlantic, Black Sea, and river runoff) mass fluxes, we compared it with the P–E determined from meteorological data to estimate the annual cycle of the horizontal flux.