CFCs

The first CFC11 and CFC12 measurements originate from 1982 (HUDSON 82 cruise, Bullister and Weiss [1983], Wallace, unpublished data). The only other CFC data set collected during the 1980s was reported by Rhein [1991] (VALDIVIA 1989 data). CFC11 and CFC12 were measured during all JOHAN HJORT cruises between 1991 and 1994. Due to analytical problems, CFC12 data are not available from the 1991 cruise. The time series of both CFCs show roughly the same features (Figs. 2 g and h). At the surface, the concentrations increase from 3.5 pmol/kg (CFC11) and 1.7 pmol/kg (CFC12) in 1982 to 7.0 pmol/kg (CFC11) and 3.0 pmol/kg (CFC12) in 1994, due to the increasing atmospheric CFC concentrations. CFC concentrations of intermediate waters show a similar trend. Below 2250m depth, CFC12 remained practically constant (0.39 pmol/kg in 1982; 0.42 pmol/kg in 1994). The 0.8 pmol/kg isoline (CFC11) deepened from 2600m in 1989 to about 3300m in the early 1990s suggesting a very slight increase of the CFC11 concentration. Below about 3300m, no significant CFC11 concentration difference between 1982 and 1994 was observed.

Fig. 2: Time series of (g) CFC 11 and (h) CFC 12 in the central Greenland Sea. The time series are presented as sections with time as the horizontal and depth as the vertical axes. The color bars are chosen to reflect changes in the deep water. Each year marker indicates the first of January of the particular year.