Steric sea level variations during 1957-1994: Importance of salinity

Spatially averaged (50°S–65°N) temperature and salinity changes in the 0–3000 m layer during the 1957–1994 period resulted in a sea level rise at a mean rate of about 0.55 mm per year. About 10% of this rate is due to a decrease of the volume mean salinity. The magnitude of total steric sea level (TSSL) changes and the ratio of thermosteric and halosteric anomalies to TSSL anomaly are nonuniform geographically. Salinity effects are critically important to the TSSL changes in some regions of the ocean. For example, the thermosteric anomaly is nearly compensated by the halosteric anomaly in the subpolar North Atlantic. This fact will cause erroneous heat content estimates based on altimetric observations from space if a climatological salinity is assumed. Based on the present historical archive of salinity data, a decrease in global mean salinity has occurred. This increase of fresh water would cause sea level rise at a rate of 1.3 ± 0.5 mm/yr if the added water comes from sources other than floating sea ice.