Sea Surface Salinity Reemergence in an Updated North Atlantic In Situ Salinity Dataset

Monthly sea surface salinity (SSS) fields are constructed from observations, using objective mapping on a 1 degrees x 1 degrees grid in the Atlantic Ocean between 30 degrees S and 50 degrees N in the 1970-2016 period in an update of the dataset of Reverdin et al. Data coverage is heterogeneous, with increased density in 2002 when Argo floats become available, high density along Voluntary Observing Ship lines, and low density south of 10 degrees S. Using lag correlation, the seasonal reemergence of SSS anomalies is investigated between 20 degrees and 50 degrees N in 5 degrees x 5 degrees boxes during the 1993-2016 period, both locally and remotely following the displacements of the deep mixed layer waters estimated from virtual float trajectories derived from the daily AVISO surface geostrophic currents. Although SSS data are noisy, local SSS reemergence is detected in about one-half of the boxes, notably in the northeast and southeast, whereas little reemergence is seen in the central and part of the eastern subtropical gyre. In the same period, sea surface temperature (SST) reemergence is found only slightly more frequently, reflecting the short data duration. However, taking geostrophic advection into account degrades the detection of remote SSS and even SST reemergence. When anomalies are averaged over broader areas, robust evidence of a second and third SSS reemergence peak is found in the northeastern and southeastern parts of the domain, indicating long cold-season persistence of large-scale SSS anomalies, whereas only a first SST reemergence is seen. An oceanic reanalysis is used to confirm that the correlation analysis indeed reflects the reemergence of subsurface salinity anomalies.

Automated summary

The monthly sea surface salinity (SSS) fields were constructed using observations in the Atlantic Ocean and analyzed for seasonal reemergence of anomalies. The study found evidence of local SSS reemergence in about half of the boxes, with less reemergence in the central and eastern subtropical gyre.