Characteristics of the seasonal cycle of surface layer salinity in the global ocean.

The seasonal variability of surface layer salinity (SLS), evaporation (E), precipitation (P ) and E -P over the global ocean is examined using in situ salinity data and the National Center for Environmental Prediction's Climate System Forecast Reanalysis. Sea- 5 sonal amplitudes and phases are calculated using harmonic analysis and presented in all areas of the open ocean between 60° S and 60° N. Areas with large amplitude SLS seasonal variations include: the intertropical convergence zone in the Atlantic, Pacific and Indian Oceans; western marginal seas of the Pacific; and the Arabian Sea. The median value in areas that have statistically significant seasonal cycles of SLS 10 is 0.19. Between about 60° S and 60° N, 37% of the ocean surface has a significant seasonal cycle of SLS and 75% a seasonal cycle of E -P . Phases of SLS have a bimodal distribution, with most areas of the ocean peaking in SLS in either March/April or September/October. The same calculation is done with surface freshwater flux using a mixed-layer depth 15 climatology. With the exception of an area near the western boundaries of the North Atlantic and North Pacific, seasonal variability is dominated by precipitation. Surface freshwater fluxes also have a bimodal distribution, with peaks in January and July, 1-2 months before the peaks of SLS. The amplitudes and phases of SLS and surface fluxes compare well in a qualitative 20 sense, suggesting that much of the variability in SLS is due to E -P forcing. However, the amplitudes of SLS are somewhat larger than would be expected and the peak of SLS comes typically about one month earlier than expected. The differences of the amplitudes of the two quantities is largest in such areas as the Amazon River plume, the Arabian Sea, the ITCZ and the eastern equatorial Pacific and Atlantic, indicating 25 that other processes such as ocean mixing and lateral transport must be important, especially in the tropics. [ABSTRACT FROM AUTHOR]