In Figure 6.39 (overleaf), the two sections of CFC-12 concentration, made 10 years apart, show vividly how surface water has been mixed downwards to varying extents at different locations in the North Atlantic. The high concentrations at 50° N correspond to Labrador Sea Water which, having been carried down to 1000-2000 m depth by winter convection, has then spread southwards and eastwards across the ocean.
Figure 6.39 Sections of CFC-12 concentration, made along ~ 20° W, from Iceland to 20° N, (a) in 1988, from RV Oceanus, and (b) in 1998, from RV Discovery. During the intervening ten years, surface water has mixed down from the surface to varying extents, depending on the latitude. In (b), the high concentrations at 1000-2000 m depth at - 50°-55° N correspond to CFC-12 which dissolved in the surface waters of the Labrador Sea and was carried down by deep convection, before spreading across to intersect the transect along 20° W. (In both sections, the ticks along the bottom indicate the locations of the hydrographie stations.)
1800 J 2400 f 3000 | 3600 4200
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