Continuous Estimate of Atlantic Oceanic Freshwater Flux at 26.5°N

The first continuous estimates of freshwater flux across 26.5 degrees N are calculated using observations from the RAPID-MOCHA-Western Boundary Time Series (WBTS) and Argo floats every 10 days between April 2004 and October 2012. The mean plus or minus the standard deviation of the freshwater flux (F-W) is -1.17 +/- 0.20 Sv (1 Sv 10(6) m(3) s(-1); negative flux is southward), implying a freshwater divergence of -0.37 +/- 0.20 Sv between the Bering Strait and 26.5 degrees N. This is in the sense of an input of 0.37 Sv of freshwater into the ocean, consistent with a region where precipitation dominates over evaporation. The sign and the variability of the freshwater divergence are dominated by the overturning component (-0.78 +/- 0.21 Sv). The horizontal component of the freshwater divergence is smaller, associated with little variability and positive (0.35 +/- 0.04 Sv). A linear relationship, describing 91% of the variance, exists between the strength of the meridional overturning circulation (MOC) and the freshwater flux (-0.37 - 0.047 Sv of F-W per Sverdrups of MOC). The time series of the residual to this relationship shows a small (0.02 Sv in 8.5 yr) but detectable decrease in the freshwater flux (i.e., an increase in the southward freshwater flux) for a given MOC strength. Historical analyses of observations at 24.5 degrees N are consistent with a more negative freshwater divergence from -0.03 to -0.37 Sv since 1974. This change is associated with an increased southward freshwater flux at this latitude due to an increase in the Florida Straits salinity (and therefore the northward salinity flux).