Mean Structure and Large-Scale Variability of the Subtropical Underwater in the North Atlantic

This study investigates the mean property distribution and large scale variability of the high salinity subtropical underwater (STUW) in the North Atlantic, using recently available Argo profiles at observed levels. Our analysis indicates that, once subducted, the STUW spreads in the subtropical North Atlantic as a vertical salinity maximum near 25.5 kg m-3. Both annual and interannual variability is identified in the STUW along the 25.5 kg m-3 density surface, which is completely different from the basin-scale variability in sea surface salinity. The annual and interannual variability in the STUW, however, shows a good correspondence with the sea surface salinity variability in the region enclosed by the 37.0 psu isohaline. Because of the formation of the STUW, this surface variability can be conveyed into the thermocline and transported over the entire basin. The effects of climate modes on the large-scale variability of the STUW are discussed.