Variations in Salinity over the Global Ocean from Multiple Gridded Argo Products

During the Argo period, the salinity over the global ocean increases in the upper ocean since 2005 with large spatial variability. Using Argo-based gridded products and ocean state estimates from the project on Estimating the Circulation and Climate of the Ocean (ECCO), an assessment of annual and interannual variability, and decadal changes in salinity in the upper 2000 m of the ocean was conducted to investigate the robust features and disagreements within two depth intervals (0-700 m and 700-2000 m), as well as at the sea surface. Though some global and regional features are relatively reproducible, obvious discrepancies are found particularly for the deeper layer. These discrepancies are not apparent on the long-term trend patterns, but are evident on month-to-month variations. For instance, the potentially undersampled current systems in the North Atlantic and Southern Ocean are one of the main reasons for the observed discrepancies. The gridded products from Scripps, JAMSTEC and Met Office show large deviations from the ensemble mean, particularly in regions like the Atlantic Ocean and the tropical Pacific. Large disagreements are found in the first and final years, which can lead to different estimates on global mean trends. This study can serve as a useful reference on how to utilize and improve the existing gridded salinity products, as well as the deep Argo program.