This paper deals with the mesoscale variability of water masses in the Greenland Sea and its implications for bottom water formation. The results are based on two conductivity-temperature-depth surveys performed in successive years. The same section in the central Greenland Basin was sampled in 1989 and 1990; an additional transect across Fram Strait was carried out in 1990. The transects extended from shelf to shelf with a station spacing of 18 km throughout. The data set reveals a surprisingly strong horizontal variability of space scales between 20 and 60 km in the entire Greenland Sea, not only in the frontal zones. The area investigated is subdivided into four hydrographical regimes for which mesoscale variability is discussed in detail. A noteworthy result is the major change of the deep-sea thermal structure within 1 year. The classical pattern with upward doming cold waters in the central basin was found in 1989 but was replaced by a ''capped'' structure with a warm intermediate layer in 1990. The implications of the observed changes are discussed with respect to deep water formation. A mechanism, based on differential compressibility, is proposed which is able to introduce negative heat input selectivity into the bottom layer. It is shown that the fine structure of temperature profiles observed in summer can be used as a tracer for the occurrence of deep convection during the preceding winter. Convective depths are concluded of about 2200 m for 1989 and of only about 250 m for 1990. ¿ American Geophysical Union 1993