Ocean Science www.ocean-sci.net 1812-0784 1812-0792 6 3 2010 10.5194/os-6-775-2010 http://www.ocean-sci.net/6/775/2010/ http://www.ocean-sci.net/6/775/2010/os-6-775-2010.html http://www.ocean-sci.net/6/775/2010/os-6-775-2010.pdf 775 787 2010-08-24 Seasonal cycles of surface layer salinity in the Pacific Ocean F. M. Bingham binghamf@uncw.edu G. R. Foltz M. J. McPhaden Center for Marine Science, Univ. of North Carolina Wilmington, 601 S. College Rd., Wilmington, NC 28403-5928, USA Joint Institute for the Study of Atmosphere and Ocean, Univ. of Washington, 3737 Brooklyn Ave NE, P.O. Box 355672, Seattle, WA 98105-5672, USA NOAA/Pacific Marine Environmental Laboratory, 7600 Sand Point Way NE, Seattle, WA 98115, USA The seasonal variability of surface layer salinity (SLS) is examined in the Pacific Ocean between 40° S and 60° N using a variety of data sources. Significant seasonal cycles were found in 5 regions: 1) The western North Pacific, 2) The northeastern North Pacific and Alaska gyre, 3) the intertropical convergence zone (ITCZ), 4) an area of the central North Pacific north of the Hawaiian Islands, 5) the central South Pacific along 10–20° S. Amplitudes range from 0.1 to > 0.5. The largest amplitudes are in the tropical band and the western North Pacific. Maximum salinity is obtained in late (northern) winter in the western North Pacific, late winter and early spring in the northeastern North Pacific, early summer in the ITCZ area, late summer and early fall in the central North Pacific area and (austral) winter in the central South Pacific. Large areas of the Pacific have no significant seasonal variation in SLS. Seasonal variability of evaporation rate, precipitation rate and the difference between them (E-P) were calculated from the OAFlux and Global Precipitation Climatology Project datasets. Typical amplitudes of E-P are 0.1–1 × 10−4 kg m−2 s−1. The seasonal variability of E-P is largely dominated by variability in evaporation in the western North Pacific and precipitation elsewhere. The largest amplitudes are in areas along the edge of the western North Pacific and in the far eastern tropical Pacific around 10° N. Phases in these areas indicate maximum E-P in mid- to late winter in these areas of large amplitude. The closest correspondence between E-P and SLS is in the ITCZ. E-P was combined with seasonal variation of the mixed-layer depth to calculate the freshwater flux forcing term of the SLS balance equation. The term was found to be similar in magnitude and distribution to E-P. Some other terms of the SLS balance were calculated. Horizontal advection was found to have seasonal cycles in a region near the equator. Entrainment was found to be mostly not significant except for a small region along 2.5–7.5° N in the eastern Pacific. 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