Constant ventilation age of thermocline water in the eastern subtropical North Pacific Ocean from chlorofluorocarbon measurements over a 12-year period

Northeastern Pacific chlorofluorocarbon (CFC) data collected between 1982 a nd 1994 near Geochemical Ocean Sections Study (GEOSECS) station 1 (28.5 deg reesN, 122.5 degreesW) record decadal timescale ventilation processes of th e subtropical thermocline in this region. The CFC-12 concentration age fiel d versus potential density has been remarkably constant over the 12-year pe riod, although CFC concentrations in the upper kilometer of the water colum n have increased with time. Results from a simple one-dimensional advection -diffusion model are consistent with an advection velocity of ca. 0.8-0.9 c m s(-1) from the source area. The influence of the 1982-83 El Nino is notic eable in the 1983 observations. While the main stream of subarctic source w ater al,pears to spread southward at a constant rate, during El Nino years the influence of comparatively CFC-free tropical thermocline waters is enha nced in this region, leading to reduced vertical inventories of CFCs, but w ithout changing the apparent CFC ages as functions of potential density. Ap parent oxygen utilization rates decrease with increasing CFC age, and also appear not to have changed significantly ol er the 12-year measurement peri od.