The global oceanic freshwater cycle : a state-of-the-art quantification

Abstract

The current capabilities of quantifying the oceanic freshwater cycle are shown based on new observations from satellite data and re-analysis models for evaporation and precipitation over the ocean. For this purpose, we analyze the homogeneity and internal consistency of eight evaporation and seven precipitation products. Discontinuities are found around 1987 for all datasets, attributable to the launch of a microwave imaging satellite. Based on a review of comparisons with independent data and these analyses, the Global Precipitation Climatology Project (GPCP) and the Objectively Analyzed Ocean-Atmosphere Fluxes (OAFlux) evaporation product are combined with a state-of-the-art river discharge dataset to produce a new estimate of the global oceanic freshwater cycle for 1987-2006. The annual mean precipitation into the ocean averaged over 19 years is estimated at 12.2±1.2 Sv, the evaporative loss at 13.0±1.3 Sv, and the total freshwater input from land at 1.25±0.1 Sv. The oceanic budget closes within the errors estimated for each data set with an imbalance of 0.5±1.8 Sv. Based on this quantification, the global patterns of oceanic freshwater fluxes are described and a global mean is integrated to provide estimates of freshwater fluxes between basins. We find the Atlantic to be less evaporative and the Pacific less precipitative than previous in-situ estimates.