Tracer data (mainly tritium and 3He, with some CFC-11/CFC-12 data) were collected between 1972 and 1988 at stations located in the Greenland and Norwegian seas (Figure 19). A small data set was also collected in the Eurasian Basin of the Arctic Ocean in 1984 and 1987 (Figure 19). The tracer concentrations in the deep waters (depth > 1500 m) of the Greenland and Norwegian seas are relatively homogeneous. Therefore, the concentrations in Greenland
Sea Deep Water (GSDW) and Norwegian Sea Deep Water (NSDW) can be averaged for each survey. The time series of the averaged tritium and CFC-11 data of GSDW (Schlosser et al., 1991; Rhein, 1991; see Figure 20) show that the tritium concentration follows closely the curve expected from radioactive decay of tritium between 1980 and 1988, while the CFC-11 concentrations remained constant between 1982 and 1989. In addition, the tritium/3He age of GSDW increased more or less linearly between 1980 and 1988. These results suggest that almost no deep-water formation took place in the Greenland Sea in the period between 1980 and 1989.
A change in deep-water production was suggested as well by observations of temperature and salinity (GSP, 1990; Clarke et al., 1990). However, the salinity signals are small (of the order of 0.005 psu), and the T/S signal is definitely