Subtropical mode water is formed in winter-time deep mixed layer due to variations in air-sea processes. In the South Atlantic, three formation cores are identified between 30oS and 40oS: in the west, in the east, and north of the Subtropical Front. Each one of these three types presents typical mean thickness and horizontal distribution patterns, mainly because of local dynamic and thermodynamic characteristics of each part of the basin. In this study we assess the effects of momentum, freshwater and radiative fluxes on the variation in volume and composition of the South Atlantic Subtropical Mode Water (SASTMW). Sensitivity experiments were designed using the National Center for Atmospheric Research Community Earth System Model. Multiple one-year simulations are forced with varying intensity of wind, precipitation and shortwave radiation. By comparing to a control run, we were able to determine that the water volume variations in the east (SASTMW type 1) and south (SASTMW type 3) are significantly affected by precipitation and shortwave radiation, and thus are more sensitive to thermodynamic processes. On the other hand, SASTMW type 2 has a greater relationship with dynamic processes and is influenced by the Indian–Atlantic interbasin exchanges.