Thermocline ventilation and oxygen utilization rates in the subtropical North Pacific based on CFC distributions during WOCE

Thermocline ventilation rates for the subtropical North Pacific are determined using a 1-dimensional (meridional) along-isopycnal advective-diffusive model tuned to chlorofluorocarbon (CFC) concentrations measured along 152 degrees W in 1991 during WOCE P16. Mean southward advection rates in the subtropics range from 1.03 to 0.56 cm s(-1) between sigma(theta) = 25.5 and 26.6. Model-derived ventilation times for the subtropical gyre increase from about 10 to 27 years for that isopycnal range. Oxygen utilization rates (OURs) determined using the advective-diffusive model decrease with depth from 6.6 to 3.2 mu mol kg(-1) yr(-1) between sigma(theta) = 25.5 and 26.6, Extrapolation of the OUR versus depth trend to the base of the euphotic zone with the 1/Z power function of Martin et al. (1987) and integration from 500 to 100 m depth implies a carbon export rate from the overlying euphotic zone of 2.2 +/- 0.5 moles C m(-2) yr(-1) at 30 degrees N, 152 degrees W. Analysis of the WOCE radiocarbon and salinity distributions indicates that zonal and cross-isopycnal transport terms would have to be considered in modeling these tracers in the subtropical North Pacific. (C) 1999 Elsevier Science Ltd. All rights reserved.