A continuous and very detailed deuterium profile was obtained from the analysis of about 900 firn samples from the south pole representing the snow accumulated over the last 100 years. Seasonal variations are well preserved in the firn, allowing the samples to be dated back to 1887 with an accuracy probably better than 5 years. This dating is consistent with the results of other independent methods, such as stratigraphic observations (back to 1927) and artificial β radioactivity and tritium measurements (back to 1955). The resulting mean annual accumulation over the 1887--1978 period is equal to 9.2 g cm-2. The value between 1887 and 1957 (9.5 g cm-2) is significantly higher (30% and 40%) than values previously obtained at the same site over comparable time spans. A decrease in annual snow accumulation is deduced from a comparison of the 1887--1930 and 1930--1978 periods (from 10.0 to 8.5 g cm-2). From a thorough examination of data relaive to the very well documented 1957--1978 period, mean annual and maximum deuterium values and annual deuterium amplitude are shown to be correlated with the corresponding mean annual and summer temperatures and the annual temperature amplitude. The degree of correlation depends on the tropsopheric level considered. On the other hand, winter temperature and deuterium minima are poorly correlated, which is attributable to the large temperature inversion during winter. Experimental temperature-isotope (D and 18O) gradients are consistent with theoretical gradients, taking into account that snow formation is a nonequilibrium process. As a whole, this work is very encouraging for the use of stable isotopes as a tool for past temperature reconstruction over periods for which only weak variation are expected. This is applied over the 1887--1978 period to the mean annual, winter, and summer temperatures along with the annual temperature amplitude.