Analysis of 26 years of bathythermographic data is used to describe the connection between the sea surface temperature and the layer depth in the western South Atlantic, off the Argentinian coast. The area is influenced by the presence of two water masses, subtropical waters and subantarctic waters. A seasonal analysis was carried out for 5¿ squares. The plotting of mixed layer depth versus surface temperature provides two types of patterns. Evidence suggests that they might be related to the presence of each of the above-mentioned water masses. A clear relationship was found for data distribution in each subarea. The exponential function L=a exp(-bTs) was found to fit best the dependence of the mixed layer depth (L) on the surface temperature (Ts). Very different ranges were empirically found for the real constants a and b depending on the predominant water mass in each subarea.