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[1] Taking advantage of the rapid advance in ocean modeling, this study investigates the sea surface salinity maximum in the North Atlantic, using results from a model of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO). Salinity budget terms were computed at the model's integration time step and archived as monthly averages. The simulated mixed layer salinity budget provides the first quantitative evidence for the ocean's role in governing the sea surface salinity maximum in the North Atlantic. Our analysis reveals that ocean dynamics explains about half of the sea surface salinity variance, being of equal importance as surface forcing. The sea surface salinity maximum varies both seasonally and interannually, as a consequence of interplay among surface flux, advection, and vertical entrainment. Contribution from eddies and small-scale processes is relatively weak but not negligible. These results may provide useful hints for the design and interpretation of future observations in the region.

The origin and pathway of the thermostad water in the eastern equatorial Pacific Ocean, often referred to as the equatorial 138C Water, are investigated using a simulated passive tracer and its adjoint, based on circulation estimates of a global general circulation model. Results demonstrate that the source region of the 138C Water lies well outside the tropics. In the South Pacific, some 138C Water is formed northeast of New Zealand, confirming an earlier hypothesis on the water's origin. The South Pacific origin of the 138C Water is also related to the formation of the Eastern Subtropical Mode Water (ESTMW) and the Sub-Antarctic Mode Water (SAMW). The portion of the ESTMW and SAMW that eventually enters the density range of the 138C Water (25.8 , s u , 26.6 kg m 23 ) does so largely by mixing. Water formed in the subtropics enters the equatorial region predominantly through the western boundary, while its interior transport is relatively small. The fresher North Pacific ESTMW and Central Mode Water (CMW) are also important sources of the 138C Water. The ratio of the southern versus the northern origins of the water mass is about 2 to 1 and tends to increase with time elapsed from its origin. Of the total volume of initially tracer-tagged water in the eastern equatorial Pacific, approximately 47.5% originates from depths above s u 5 25.8 kg m 23 and 34.6% from depths below s u 5 26.6 kg m 23 , indicative of a dramatic impact of mixing on the route of subtropical water to becoming the 138C Water. Still only a small portion of the water formed in the subtropics reaches the equatorial region, because most of the water is trapped and recirculates in the subtropical gyre.