Data from a presently ongoing cruise with RV Polarstern in the context of the IPY Climate of Antarctica and the Southern Ocean (CASO) project in the Atlantic sector of the Southern Ocean extent the time series of observations of water mass properties beginning in 1989 to 2008. Measurements from moored instruments and under-ice floats complement the data set. They reveal significant temperature and salinity variations of the Warm Deep Water and the Weddell Sea Bottom Water. In the bottom water of the Weddell Sea proper a temperature increase by 0.12°C was observed over 16 years from 1989 to 2005. At the prime meridian warming occurred in the Warm Deep Water from 1984 to 1996 followed by cooling since then. The warming trend in the bottom water is detected here as well and started in 1992. The salinity of the Winter Water was subject to significant increase reducing the stability of the upper water column. The data obtained during the present cruise will allow shedding further light into the processes being the origin of the changes and help to estimate the role of decadal variability.