Arctic Ocean Ventilation Studied with a Suite of Anthropogenic Halocarbon Tracers

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Abstract
The chlorofluoromethanes (CFMs: CCl2F2 and CCl3F), methyl chloroform (CH3CCl3), and carbon tetrachloride (CCl4) have been measured in deep waters of the Arctic Ocean. Oceanic and atmospheric inventories of these compounds result from known anthropogenic releases; because the CFMs and CCl4 are also chemically nonreactive, they can be used as transient tracers of ocean circulation. The input history of CCl4 is longer than that of any other transient tracer identified to date(∼70 years). This long input history, together with an e-folding time scale of increase(τ) of ∼28 years, makes CCl4 potentially the most useful tracer for calibrating models of the oceanic uptake of the fossil-fuel CO2 transient(τ ≈ 25 years). The bottom water of the Nansen Basin, Arctic Ocean, has detectable CCl4 but undetectable CFMs and CH3CCl3, which suggests either that the bottom water is ∼50 years old, or that there is a small, nonanthropogenic component of atmospheric CCl4(<6 parts per trillion by volume).