Changes in water masses properties of Atlantic Ocean at 30ºS

Abstract

The South Atlantic is not as well studied as the North Atlantic, a large uncertainty exists on its interannual variability. This work aims to study the hydrographic variability of the South Atlantic at 30°S using the Bindoff and McDougall (1994) method. This method helps to understand whether interannual changes in the water masses are due to vertical variation of the isoneutrals or to changes in their properties. For this study, the A10 repeated hydrographic section, of the World Ocean Circulation Experiment (WOCE), has been used. This section took place in three different years 1992-2003-2011. In 1992, the ocean surface temperature is higher than in the other two years (2003 and 2011). This is due to the fact that this year there was a strong period of El Niño. During the El Niño period, warming over the South Atlantic is favored due to the weakening of the southeasterly trade winds and a strengthening of the westerlies winds. Also of this, the southward transport of tropical Ekman is reduced and contributes to the warming. Large vertical displacement of the isopycnals was found on the eastern basin from surface to intermediate levels masking the interpretation of the interannual temperature and salinity variability. These displacements were caused by the presence of the Agulhas Rings. We explore the amount and characteristics of the Agulhas Rings found in the area due to the nearby retroflection of the Agulhas Current. While Rings near the African shelf had a higher content of water masses from the Indian Ocean, those located further west on the section had higher spinning speeds. In addition, for the deep waters a shoaling of the isopycnals is observed due to an increase of salinity and temperature. This can be relationated with an increase of Antarctic Sea Ice.