Chlorofluorocarbons in the Sea of Okhotsk: Ventilation of the intermediate water

Abstract

Ventilation of the intermediate layer in the Sea of Okhotsk is studied with regard to the ventilation of North Pacific Intermediate Water (NPIW). Measurements of chlorofluorocarbons (CFCs) from 1998 to 2000 reveal that the Okhotsk intermediate water is ventilated in two ways. The first consists of dense water formation in the polynyas that form on the northern shelves during winter. Measurements show that on the northwestern shelf, because of atmospheric cooling and brine rejection, the cold water that forms is dense enough to enter the intermediate layer. The CFC concentration in this dense shelf water (DSW) is high and almost saturated with respect to atmospheric CFCs, indicating that the DSW experiences active air‐water gas exchange during its formation. Away from the shelves, the CFC distribution shows that the DSW directly ventilates the upper level of the Okhotsk Sea Intermediate Water (OSIW). The second ventilation process is driven by the strong tidal mixing around the Bussol' Strait. The observed distribution of CFCs at the 27.4 σθ level suggest that diapycnal mixing around the strait transports CFCs from the surface to this deeper layer, ventilating the OSIW. Combination of both processes means that the OSIW is more ventilated than Pacific water at the same density levels.