We present helium 3 (3He) and dissolved oxygen (DO) distributions in the upper waters of the central Weddell Sea obtained from samples collected during the Winter Weddell Sea Project (WWSP, July to September 1986), and the Antarctic Zone Flux Experiment (ANZFLUX, July to August 1994). The data are discussed in terms of apparent entrainment rates of Weddell Deep Water (WDW) into the Winter Mixed Layer (WML) and the associated apparent heat flux. The fraction of WDW in the WML derived from the 3He excess (Δδ3He) and DO deficit in the mixed layer increases with latitude and reaches 10--20% at 68¿S. The corresponding apparent heat flux during the winter entrainment period is 14 ¿ 4 W m-2, and the apparent annual heat flux is 6 ¿ 4 W m-2. Significantly larger heat fluxes (winter ocean heat flux of 25 W m-2; average annual heat flux of 15 W m-2) are observed near Maud Rise and in the region southwest of the rise in features that are associated with a Taylor column that apparently forms over the seamount. The entrainment rates and heat fluxes obtained from a one-dimensional numerical model exceed those calculated from the WDW fraction in the WML by about a factor of two, mainly because of the effect of gas exchange through leads on the mass balance of 3He and DO in the WML. The best agreement between model calculations performed for 62.5¿S, 65¿S, and 67.5¿S and observations is achieved for entrainment rates of 25--35 m yr-1, 30--40 m yr-1, and 35--45 m yr-1, respectively. Daily entrainment rates are practically identical (0.28--0.39 m d-1) for the three latitudes. Corresponding simulated heat fluxes for the winter entrainment period and the annual average are 36--50 W m-2 and 10--17 W m-2, respectively. Extrapolation of the annual average heat flux to the seasonally ice-covered Weddell Sea yields a value of 0.04--0.07 PW.