Seasonal variability of salt in the western tropical Atlantic

The western boundary regime of the tropical South Atlantic Ocean is the main pathway of an important meridional transfer of warm and cold water masses that balances the global temperature on Earth, known as Atlantic Meridional Overturning Circulation (AMOC). The AMOC is a system that depends on a delicate balance of temperature and salinity effects on density, and is considered one of the main elements of the terrestrial system. The objective of this work was to study the variability of the salinity in the Western Tropical Atlantic Ocean, in order to identify salt transport anomalies in the circulation of the Atlantic Meridional Overturning Circulation as a result of climate change. Based on 3 decades of hydrographic observations of the Northern Brazilian Current and of the Deep Western Boundary Current, neutral density surfaces, salinity anomalies, geostrophic transport and salt transport were calculated. In general, the results reveal a coherent decadal change in salinity in 5°S and 11°S. In the upper ocean, both water masses, the South Atlantic Central Water and the Antarctic Intermediate Water, presented an increase of the salinity. The Antarctic Intermediate Water shows small trends with a decrease in salinity values in the upper part of the layer and an increase at the border to the North Atlantic Deep Water. In the deep ocean, the North Atlantic Deep Water layers the salinity generally decreases and, as expected for a warmer ocean in the Southern Hemisphere, the Antarctic Bottom Water layer shows an increase in salinity. The geostrophic and salt transports suggest a multidecadal variability and the changes in upper layer salinity are consistent with an increased Agulhas leakage, as described in literature. In the deep ocean, water mass changes seem to be likely related to changes in weather patterns in the North Atlantic as well as in tropical circulation changes.