A construction of pseudo salinity profiles for the global ocean: Method and evaluation

This study demonstrates a reconstruction of salinity profiles for the global ocean for the period 1993 - 2008. All available temperature-salinity (T-S) profiles from the Global Temperature-Salinity Profile Program and Argo data are divided into two subsets; one half is used for producing the vertical coupled T-S empirical orthogonal function (EOF) modes, and the other half is used for the verification. We employed a weighted least-squares method that minimizes the misfits between the predetermined EOF structures and independent observed temperature and altimetry data. Verification shows that the South Indian and North Atlantic oceans maintain good correlations to 900 m depth between the observed and reconstructed salinity with altimetry data. Meanwhile, the Pacific and Antarctic oceans below 500 m shows significant negative correlations which are associated with the relationship between steric height and salinity variability in these basins. In order to guarantee general agreement with observations for all ocean depths, we calculate a regional correlation index considering the impact of altimetry data and employ it for our final products. Except for the surface ocean, the pseudo salinity profiles show general improvements compared to the existing climatology and the reanalysis outputs from the Geophysical Fluid Dynamics Laboratory's ensemble coupled data assimilation system. Near the surface layer, reanalysis outputs show a relatively high performance due to the coupling between the atmosphere and ocean. An assimilation system produces reliable surface flux variability not accounted for the construction of the global pseudo salinity profiles. These results encourage the application of the global pseudo salinity profiles into an assimilation system for the 20th century when the observed salinity data are sparse.