HR: 0800h
AN: OS31A-0553    [Abstracts]
TI: Interannual Variability of Chlorofluorocarbons, pCFC Ages and Ideal Ages in the North Pacific from 1958-2000 as Simulated by an Ocean General Circulation Model
AU: * Tsumune, D
EM: tsumune@criepi.denken.or.jp
AF: Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko, 270-1194 Japan
AU: Bryan, F O
EM: bryan@ncar.ucar.edu
AF: National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307 United States
AU: Doney, S C
EM: sdoney@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Road, Woods Hole, MA 02543 United States
AU: Hecht, M W
EM: mhecht@lanl.gov
AF: Los Alamos National Laboratory, MS B296, MS B296, NM 87545
AU: Nakashiki, N
EM: nakasiki@criepi.denken.or.jp
AF: Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko, 270-1194 Japan
AB: Chlorofluorocarbon (CFCs) concentrations and ideal age are simulated in a global integration of the Parallel Ocean Program (POP) with realistic surface forcing derived from the NCEP/NCAR reanalysis (1958-2000). The present study focuses on the subtropical and subpolar thermocline of the North Pacific where the simulated CFC concentration fields are in reasonably good agreement with WOCE observations. Tracer ventilation ages are computed from the simulation using the CFC partial pressure (pCFC) and CFC-11/CFC-12 ratio approaches. Biases arise in pCFC ages due to the interaction of mixing with the non-linear CFC atmospheric time-histories, and the model tracer ages significantly underestimate ideal age in the mid to lower thermocline and in the shadow zone of the eastern tropics/subtropics. The spatial patterns in the pCFC age errors are consistent with earlier studies using more idealized models, but the magnitude of the error is considerably larger, with the tracer/ideal age ratio approaching a factor of 5-7 compared to 1.5-2 as estimated perviously. Variability in pCFC ages is well correlated with variability of ideal age on interannual timescales, though the amplitude of the pCFC variability may be substantially less due to the offsets in the tracer/ideal age. For ideal ages greater than 15-20 years, age variability is also well correlated with that of potential vorticity. The significant interannual variability in tracer ages and longer-term temporal trends in the tracer age biases complicate the interpretation of CFC data collected from repeat occupations on 5 to 10 year intervals as currently envisioned by CLIVAR. In particular, the tracer age differences from the instantaneous samples are likely not representative, at least directly, of interdecadal variability in ocean ventilation.
DE: 4805 Biogeochemical cycles (1615)
DE: 4806 Carbon cycling
DE: 4845 Nutrients and nutrient cycling
DE: 4215 Climate and interannual variability (3309)
DE: 4532 General circulation
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting