Opposite‐Sign Sea Surface Salinity Anomalies Over the Northeastern and Southwestern South Atlantic Ocean From 2010 to 2017

Using seven sea surface salinity (SSS) data sets, the dominant modes of interannual SSS variability over the South Atlantic Ocean are examined for the period 2010–2017, which features strong anomalies (>0.1 g/kg). The empirical orthogonal function analysis and composite analysis are used, and the results show that the South Atlantic Ocean features opposite‐sign SSS anomalies over the southwestern (45°–20°S/40°–60°W) and northeastern (0°–15°E/0°–15°S) regions. SSS budget analyses based on the Estimating the Circulation and Climate of the Ocean model estimate suggest that horizontal advection promotes the opposite‐sign SSS anomalies over the two regions. The interannual changes in the horizontal advection can be attributed to changes in the advection of mean salinity by the anomalous horizontal flow, in which the Ekman velocities play the dominant role. The anomalous wind stress and sea level pressure patterns suggest that the opposite SSS variations in poles A and B are probably associated with atmospheric forcings under alternating Atlantic Nino and Benguela Nina conditions. This study offers a connection in interannual SSS variations over two remote regions within the South Atlantic Ocean and suggests the possible role of the climate mode in setting up interannual salinity anomalies over the South Atlantic Ocean. Plain Language Summary Sea surface salinity (SSS) is vital to ocean dynamics in the ocean's upper layers and is used to denote changes in climate patterns. Recent analyses have explored the variability in SSS over the global ocean, but the interannual SSS variations over the South Atlantic Ocean are the least understood. This study finds that the interannual SSS anomalies generally show opposite signs over the northeastern (in the vicinity of the Congo River mouth) and southwestern sections (in the vicinity of the La Plata mouth) of the South Atlantic Ocean. A budget analysis finds that the horizontal advection associated with anomalous current promotes the construction of the opposite‐sign SSS anomalies over the two regions. Then, the interannual SSS variability was linked to the atmospheric conditions associated with two South Atlantic climate modes (Atlantic Niño and Benguela Niña) through wind‐driven flows. Key Points The interannual sea surface salinity (SSS) anomalies over the northeastern and southwestern regions show opposing signs from 2010 to 2017 Horizontal advection promotes the opposite‐sign SSS anomalies over the two regions The opp