OceanObs’09 Community White Paper Proposal Title Salinity and the Global Water Cycle Lead author R. Schmitt, Woods Hole Oceanographic Institution Woods Hole, MA 02540 508 289 2426 [email protected] Contributing authors T. Boyer (NOAA) Y. Chao (JPL) R. Curry (WHOI) A. Gordon (LDEO) N. Bindoff (UTAS) S. Wijffels (CSIRO) J. Church (CSIRO) G. Reverdin (LODYC) M. Palmer (Hadley Center) G. Lagerloef (ESR) L. Yu (WHOI) Description In terms of area and magnitude, the global water cycle is overwhelmingly an oceanatmosphere phenomenon, yet most studies have focused on the much smaller terrestrial component. Here we show that sea surface salinity has much to tell us about the global water cycle. We review evidence from oceanic salinity data from all ocean basins that the water cycle is changing and connect it to trends in estimates of surface fluxes. We further discuss the important interplay between surface water fluxes and upper-ocean mixing processes that arises from buoyancy physics. Connections to water mass formation processes and the stability of the thermohaline circulation are also treated. The strong non-linear dependence of the vapor pressure of water on temperature leads to predictions of an enhanced hydrologic cycle resulting from global warming, which has helped to motivate plans for new salinity sensing satellites SMOS and Aquarius. The in-situ observational requirements for these programs will be discussed, along with the opportunities provided for new field programs examining the details of the upper-ocean processes affecting sea surface salinity.