On the use of carbon tetrachloride as a transient tracer of Weddell Sea deep and bottom waters

Abstract

Antarctic bottom waters have long been known to be a mixture of Circumpolar Deep Water and Shelf Water. Recent observations show that in the Antarctic bottom waters of the Scotia Sea and northern Weddell Sea, the ratios of carbon tetrachloride (CCl4) to chlorofluorocarbons (CFC‐11, 12) are inconsistent with the ratios observed in the surface layer of the Weddell Sea. This is the result of a deficit of CCl4 in the bottom waters, and renders the compound unsuitable for use as a transient tracer from which apparent ages can be derived directly. The summer near‐surface temperature minimum of Antarctic Surface Water exhibits a similar inconsistency, demonstrating that CCl4 can be removed from cold waters with high oxygen levels, probably through a biological process. It is inferred that Shelf Water features a similar CCl4 deficit which is transferred to the new Antarctic bottom waters upon formation, accounting for the observed deep CCl4 deficit.