Figure 6.38 (a) Changes in the atmospheric concentrations of CFC-11, CFC-12 and CFC-113 between 1930 and 2000.

(b) Changes in the CFC-11: CFC-12 ratio and the CFC-113: CFC-11 ratio, up until 2000. As CFC-11: CFC-12 ratios have remained more or less constant since 1977, they are not very useful for 'ageing' recently formed water masses.

(c) Concentration profiles of CFC-11, CFC-12 and dissolved oxygen, in the South Atlantic at about 55° S. (1 pmol (= picomol) is 10-12 mol.) Note that despite its lower concentrations in the atmosphere, CFC-11 has higher concentrations in seawaterthan does CFC-12 because it is more soluble. These observations were made in the late 1980s.

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