Vertical profiles of CCl3F (F‐11) and CCl2F2 (F‐12) in the central Arctic Ocean basin

The anthropogenic chlorofluoro‐methanes CCl3F (F‐11) and CCl2F2 (F‐12) have been measured to depths of 1800 m in the Canada Basin of the Arctic Ocean (approximate position 85°50′N, 108°50′W). The measurements were made as part of the Canadian Expedition to Study the Alpha Ridge (CESAR) during April 1983. Surface layer concentrations beneath the ice were 4.79×10−12 mol/kg (F‐11) and 2.11×10−12 mol/kg (F‐12). Both profiles exhibit a rapid concentration decrease with depth through the halocline and very low, but detectable, concentrations at depths of 350–900 m in the Atlantic Layer. In the Arctic Ocean Deep Water (900–1800 m), concentrations are at or below our practical detection limit of 0.01×10−12 mol/kg. The profiles have been interpreted using two “extreme‐case” lateral ventilation models in order to place bounds on the water column ventilation rates. The “Ventilation age” of the upper portion of the halocline (60–150 m) increases with depth from 4 to 14 years. The core of the Atlantic Layer at this location appears to have been isolated from the surface for at least 30 years.