Barrier layer in the North Pacific subtropical gyre

By analyzing all the available temperature/salinity profiles obtained by Argo floats as of August 2003, we evaluate the barrier layers (BLs) in the North Pacific subtropical gyre. 20.5% of the profiles at 10°-25°N have BLs with thickness greater than 10 m. The relative frequency and typical thickness of the BLs are generally higher and greater, respectively, during January-May, which are consistent with the wider distribution of the previously reported climatological BL in winter and spring. Because evaporation dominates over precipitation in winter, we infer that the subduction of high saline water, known as North Pacific Tropical Water, is responsible for the BL formation in 10°-25°N, at least in winter. Patchy occurrence of the BLs detected by the floats, and locally confined intense salinity fronts in several synoptic sections, suggest that the BLs are formed by the subduction at those sharp salinity fronts.