ALBERT

Description: The surface ocean hydrological cycle is explored based on ∼300 new δ 18 O and δD measurements from surface waters of the Atlantic Ocean and the Mediterranean Sea over the period 2010-2016. Our approach combines these surface observations with salinity (S) and stable isotope measurements of atmospheric water vapor. The distinct regional S-δ distributions are used to identify different surface water masses and their horizontal advection. Moreover, based on assumptions on the δ-S characteristics of seawater sources and the isotope composition of the evaporative (δ e ) and meteoric water (δ MW ) fluxes, the δ-S distribution is used to indicate the relative importance of evaporation (E) and meteoric water inputs (MW). Here, δ e is estimated from the Craig and Gordon's equation using 120 days of measurements of the ambient air above the Atlantic Ocean collected during three cruises. To provide quantitative estimates of the E:MW ratio, we use the box model from Craig and Gordon (1965). This identifies the subtropical gyre as a region where E:MW ∼2 and the tropical ocean as a region were MW:E ∼2. Finally, we show that the δ 18 O-δD distribution is better represented by a linear fit than the δ-S relationship, even in basins governed by different hydrological processes. We interpret the δ 18 O-δD distribution considering the kinetic fractionation processes associated with evaporation. In the tropical region where MW exceeds E, the δ 18 O-δD distribution identifies the MW inputs from their kinetic signature, whereas in regions where E exceeds MW, the δ 18 O-δD distribution traces the humidity at the sea surface.