A one-dimensional (1-D) mixed layer model (the Chen scheme) was applied in the Subantarctic Zone (SAZ) and the Polar Frontal Zone (PFZ) to simulate the upper ocean dynamics. The model was forced with 4 years data of the heat fluxes, freshwater fluxes, and wind stresses from the National Centers for Environmental Prediction. In both the SAZ and PFZ, the 1-D model was capable of reproducing the amplitude of the seasonal sea surface temperature (SST) and the seasonality of the mixed layer depth (MLD). The shallowest MLD was found in January-February (20 m in the SAZ, 35 m in the PFZ), and the deepest MLD was found between August and October (600 m in the SAZ, 160 m in the PFZ). The summer MLD was shallower in the SAZ than in the PFZ due to the lower wind stress. However, the shallower winter MLD in the PFZ than in the SAZ was due to the strong stratification in the water below the mixed layer. In the SAZ, variability in the wind stress was the dominant term driving the fluctuation in MLD in the summer, but variability in the heat flux was the major factor controlling the timing of the deepening and shoaling of the mixed layer in the winter. In the PFZ both the variability in the wind stress and the heat flux dominated the variability of the MLD in both the summer and the winter. ¿ 2001 American Geophysical Union