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

Abstract

[1] 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.Citation: García, D., B. F. Chao, J. Del Río, I. Vigo, and J. García-Lafuente (2006), On the steric and mass-induced contributions to the annual sea level variations in the Mediterranean Sea,

Steric Sea-level Variations Inferred from Combined Topex/Poseidon Altimetry and GRACE Gravimetry

“…A similar behaviour has also been observed in previous studies of the global ocean (Chen et al, 1998, Minster et al, 1999, Cazenave et al, 2000, as well as in local studies like that of the Mediterranean Sea (Garcia et al, 2006). This difference in phase means that the water budget of the ocean is at a minimum when the steric sea level, and thus the heat content in the ocean, is at a maximum.…”

Steric and mass-induced Mediterranean sea level trends from 14 years of altimetry data

“…The use of global circulation models and assimilation techniques along with new satellite missions such as Gravity Recovery And Climate Experiment (GRACE) provide new tools to achieve independent estimations of each contribution. Recently, García et al (2006) and Fenoglio-Marc et al (2006) have accomplished such separation in the Mediterranean Sea for the annual cycle and have shown a remarkable agreement between the seasonal ξ M estimated as ξ T − ξ S from (1) and the direct estimation from GRACE data. The knowledge of the spatial and temporal relative importance of these contributions in sea level trends will lead to valuable understanding of the ocean dynamics and global climate change.…”

“…Peaks of ξ T and ξ M are ∼ 2-month out of phase leading to the rather unexpected result already mentioned by García et al (2006) that, during a part of the rising phase of the sea level seasonal cycle, the Mediterranean is losing mass and vice-versa. We lack of a definite explanation for this behaviour although it can be linked to the annual production of deep water, particularly WMDW in the western Mediterranean basin.…”

“…Using Eq. (4), an annual amplitude of 37 ± 6 mm/month is obtained for F. García et al (2006) and FenoglioMarc et al (2006) have also evaluated δ(ξ M ) during the period 2002-2004 calculated from GRACE data and compared it with the monthly (P-E) field averaged over the Mediterranean in the same period to estimate annual amplitudes of 18 mm/month and 60 mm/month, respectively. These values can be compared with historical results as reported by García-Lafuente et al (2002) from in situ measurements between 10/95 and 05/98, who observe an annual amplitude of 78 ± 44 mm/ month.…”

Recent observations of seasonal variability of the Mediterranean outflow in the Strait of Gibraltar

“…The net flow has a seasonal cycle whose maximum is observed in summer [Bryden et al, 1994;Candela, 2001;García Lafuente et al, 2002a], whose likely origin resides in the fact that the seasonal cycles of inflow and outflow do not cancel each other on monthly time-scales. This seasonal input of mass-excess into the Mediterranean Sea is neither canceled out by the evaporative cycle on monthly basis [García Lafuente et al, 2002a, giving rise to a seasonal cycle of mass content in the Mediterranean, which adds on to the steric one due to the solar heating, and that has been recently identified by García et al [2006] using gravity observations (Gravity Recovery And Climate Experiment -GRACE-Mission).…”