The contrast between Atlantic and Pacific surface
5 The Atlantic Ocean is known to have higher sea surface salinity than the 6 Pacific Ocean at all latitudes. This is thought to be associated with the 7 Atlantic Meridional Overturning Circulation and deep water formation in 8 the high latitude North Atlantic a phenomenon not present anywhere 9 in the Pacific. This asymmetry may be a result of salt transport in the 10 ocean or an asymmetry in the surface water flux (evaporation minus pre11 cipitation; E P with greater E P over the Atlantic than the Pacific. 12 In this paper we focus on the surface water flux. 13 Seven estimates of the net freshwater flux (E P R including 14 runoff, R) calculated with different methods and a range of data sources 15 (atmospheric and oceanic reanalyses, surface flux datasets, hydrographic 16 sections) are compared. It is shown that E P R over the Atlantic is 17 consistently greater than E P R over the Pacific by about 0.4 Sv (1 18 Sv 106 m3 s 1) The Atlantic/Pacific E P R asymmetry is found at 19 all latitudes between 30*S and 60*N. Further analysis with ERA Interim 20 combined with a runoff dataset demonstrates that the basin E P 21 R asymmetry is dominated by an evaporation asymmetry in the north22 ern high latitudes, but by a precipitation asymmetry everywhere south 23 of 30*N. At the basin scale, the excess of precipitation over the Pacific 24