Ocean Change: Salinity

Fluxes of evaporation (E) and precipitation (P) at the ocean surface dominate the global hydrological cycle. Transport of water through the atmosphere from one region to another are balanced in the ocean by currents moving waters of contrasting salinities. The ocean salinity field therefore is an integral part of the global water cycle and is set by atmospheric water transports (E-P). A key question is whether the changing ocean salinity field suggests clear evidence of long-term changes to the water cycle, in particular an expected intensification in response to the recent warming of Earth's surface.

CSIRO has recently published new estimates of changes to global ocean salinities for the period 1950-2008, which are based on the Argo data set combined with quality controlled historical ship-based observations. This study (Durack & Wijffels, 2010) along with others, found that increased salinities (salinification) are found in ocean regions dominated by evaporation, and decreased salinities (freshening) in ocean regions dominated by precipitation, suggesting an enhancement to the pattern of the climatological mean over the period of analysis. Subsurface change patterns also suggest that long-term water cycle changes have occurred, however, these changes are the result of water cycle change along with long-term warming, which has changed ocean water masses in the upper 1000m of the global ocean. Changes are presented as salinity change per 50-years (notionally 1950-2000) to aid comparison to previous observed and modelled estimates.

The surface salinity changes suggest that an enhancement to the global water cycle, as expressed in surface evaporation and precipitation (E-P) has occurred. The ability of climate models to reproduce these observed changes and their attribution is under investigation (e.g. Durack et al., 2012).

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