CHLOROFLUOROCARBON-11 REMOVAL IN ANOXIC MARINE WATERS

Measurements of the chlorofluorocarbons CCl3F (F-11) and CCl2F2 (F-12) made in the subsurface anoxic zones of the Black Sea and Saanich Inle t, B.C., Canada show a pronounced depletion of dissolved F-11. These z ones are strongly reducing and are characterized by the absence of dis solved nitrate (NO3-) and the presence of hydrogen sulfide (H2S). Mode ls incorporating the atmospheric input histories of these CFCs and the observed distributions are used to estimate residence times for water in these zones and first order in-situ removal rates for F-11. In con trast, measurements in the mid-depth low-oxygen zone of the eastern Pa cific (where NO3- is present and H2S is below detection limits) do not show evidence of similar rapid F-11 removal.