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The Florida Current (FC) contributes to Atlantic circulation by carrying the western boundary flow of the subtropical gyre and the upper branch of meridional overturning circulation. Repeated FC hydrographic (velocity, salinity, and temperature) sections during 1982-1987 and 2001-2015 characterize its water mass structure and associated transport variability. On average, FC volume transport comes from subtropical North Atlantic water (NAW, 44%), Antarctic Intermediate Water (AAIW, 14%), surface water (SW, 27%), and an indistinct source (Rem 15%), while salinity transport relative to the average salinity along 26 degrees N comes from NAW (55%), AAIW (0.2%), SW (30%), and Rem (15%). From 1982-1987 to 2001-2015, NAW, AAIW, and Rem salinified by 0.03-0.16 g kg(-1) and increased the salinity anomaly transport by 3%. These patterns imply that advective salt transport by the FC (1) is sensitive to subtropical North Atlantic variability and (2) is partially decoupled from the volumetric pathway of the upper overturning branch.

Plain Language Summary Surface currents in the Atlantic Ocean flow northward as part of a global overturning circulation. Overturning transports heat and salt to northern latitudes as a major contribution to global climate. At 26 degrees N in the Atlantic, almost all the northward flow is carried by the Florida Current (FC). This study uses temperature and salinity measurements of the FC in 1982-1987 and 2001-2015 to interpret what sets northward salt transport and how it changes over two decades. Below the surface, the FC has become much saltier by 0.05-0.01 g/kg. The net northward salt transport has increased by 3%, a small but significant amount. Though changes in volume transport have the potential for causing large changes in salt transport, the observations show instead that increased salt transport is driven primarily by saltier waters from the subtropical North Atlantic. FC salt transport appears to be partially decoupled from volume transport associated with overturning. These results provide evidence that changing stratification associated with saltier subtropical water does lead to changes to oceanic advection of salt on a basin scale.