Due to its large heat capacity and the exchange of heat between the ocean and the atmosphere, the ocean has a significant impact on climate. In the Atlantic, heat is transported from low latitudes northward, moderating the climate of Europe and North America. This northward heat transport is maintained by a return flow of colder deep water formed in the North Atlantic.
The Greenland Sea has long been recognized as an important region of deep water formation (e.g., Nansen [1906], Aagaard et al. [1985], Clarke et al. [1990], Schott et al. [1993]). The surface mixed layer of the central Greenland Sea starts to cool in fall reaching temperatures near the freezing point in November or December (e.g., Visbeck et al. [1995]). Subsequent sea-ice formation can increase the surface salinity due to brine release. Deepening of the mixed layer by about 1m per day (Visbeck et al. [1995]) leads to entrainment of heat and more salt from underlying waters. Continued cooling from the surface eventually can induce deep convection which under favourable conditions may reach the bottom of the Greenland Sea. The density of the surface waters shows significant interannual variability, and in some years convection does not extend below depths of a few hundred meters (Quadfasel and Meincke [1987]).
Recently, evaluation of time series of hydrographic or transient tracer data have provided evidence for decadal variability of the characteristics of Greenland Sea Deep Water (GSDW), which has been linked to changes in intensity of deep water formation (Clarke et al. [1990], Schlosser et al. [1991], Rhein [1991], Meincke et al. [1992], Bönisch and Schlosser [1995]). These studies focused on the deep water, rather than the temporal evolution of the properties throughout the entire water column, and did not simultaneously examine hydrographic and transient tracer data. They also did not attempt to examine the entire data set available for this region. The purpose of this study is to fill these gaps in the synthesis of Greenland Sea data, and, in this context, to present new data obtained on four cruises between 1991 and 1994, which considerably add to our understanding of the interannual and decadal variability in the Greenland Sea.