Uses of chlorofluorocarbons as ocean tracers and for estimating the removal rates of CFC-11 and carbon tetrachloride in certain marine environments

The removal rates of CCl{dollar}sb3{dollar}F (CFC-11) in anoxic waters and CCl{dollar}sb4{dollar} in anoxic and oxygenated waters were estimated by incubation experiments and modeling methods. Shallow oxygenated water and deeper anoxic hydrogen sulphide-bearing waters were collected from Saanich Inlet for use in incubation experiments. The anoxic incubation experiments lasted 4 months and 2.5 years at 25{dollar}spcirc{dollar}C and 8{dollar}spcirc{dollar}C respectively and indicated that the removal of CFC-11 is temperature-dependent and biologically mediated. CCl{dollar}sb2{dollar}F{dollar}sb2{dollar} (CFC-12) was found to be extremely stable under these conditions and removal was undetected over the same period of time. The removal of CFC-11 and CFC-12 was not detected in oxygenated water held at 8{dollar}spcirc{dollar}C for 2.5 years. A 10 day incubation experiment illustrated that CCl{dollar}sb4{dollar} was rapidly removed in anoxic waters. The removal rates of CCl{dollar}sb4{dollar} are temperature-dependent and biologically mediated showing a increase from 0{dollar}spcirc{dollar}C to 25{dollar}spcirc{dollar}C and a decrease from 25{dollar}spcirc{dollar}C to 40{dollar}spcirc{dollar}C. These results, together with field measurements in Saanich Inlet and Lake Nitinat, indicate that CCl{dollar}sb4{dollar} is removed much faster than CFC-11 in anoxic water, while CFC-12 behaves as a conservative tracer even in strongly anoxic hydrogen sulphide-bearing waters.; The residence times of the deep waters in two anoxic basins (the Black Sea and Lake Nitinat) were estimated by a multi-layer Horizontal Box (HB) model and a simple box model respectively, using CFC-12 as a conservative tracer.; CFC-11 and CFC-12 were used as dating tracers for estimating the oxygen utilization rates in the deep water of the Sea of Marmara and along several isopycnal layers in the South Pacific Ocean. The P{dollar}sb{lcub}rm CFC-11{rcub}{dollar} and P{dollar}sb{lcub}rm CFC-12{rcub}{dollar} apparent ages along isopycnal layers in the South Pacific are consistent with each other for water ages less than 35 years. However, P{dollar}sb{lcub}rm CCl4{rcub}{dollar} apparent ages tend to be older than P{dollar}sb{lcub}rm CFCs{rcub}{dollar} apparent age and indicate in-situ removal of CCl{dollar}sb4.{dollar} The first-order CCl{dollar}sb4{dollar} in-situ removal coefficients decreased with increasing density from {dollar}sim{dollar}0.13 ({dollar}pm{dollar}0.05) yr{dollar}sp{lcub}-1{rcub}{dollar} at {dollar}sigmasb{lcub}theta{rcub}{dollar} = 26.1 to 0.045 ({dollar}pm{dollar}0.035) yr{dollar}sp{lcub}-1{rcub}{dollar} at {dollar}sigmasb{lcub}theta{rcub}{dollar} = 27.2. The modeled CCl{dollar}sb4{dollar} removal rates are correlated with potential temperature and depth, and are lowest in cold, deep water.