Two zonal sections at 11 ¿S in the South Atlantic, separated in time by 11 years, provide temperature differences in the deep ocean. The aim of this case study is to check whether intrinsic temperature changes are sufficiently large to identify long-term water mass property variations which could be related to climate change. Potential temperature differences on isobaric surfaces in the deep ocean here reach several tenths of ¿C. They can be caused by vertical (cross-isopycnal) or horizontal (isopycnal) advection and mixing, or by intrinsic water mass changes. The effect of vertical transport is removed by using neutral (density) surfaces. The effect of horizontal transport is determined by using a mixing parameterization for temperature and silica on neutral surfaces. The residual intrinsic temperature changes are, with a few local exceptions, within the range of the ¿0.05 ¿C uncertainty, and the temperature changes can thus be explained by advection and mixing alone. ¿ 2000 American Geophysical Union