HR: 0800h
AN: OS51C-1319    [Abstracts]
TI: Reconstructing anthropogenic $\delta^{13}$C changes in the North Pacific Ocean using the MIX approach
AU: * Sonnerup, R
EM: rolf.sonnerup@noaa.gov
AF: Joint Institute for Study of the Atmosphere and Ocean, box 357941 University of Washington, Seattle, WA 98195 United States
AU: McNichol, A
EM: amcnichol@whoi.edu
AF: National Ocean Sciences AMS Facility, Department of Geology and Geophysics MS 8, McLean Laboratory Woods Hole Oceanographic Institution, Woods Hole, MA 02543-1539 United States
AU: Bullister, J
EM: john.l.bullister@noaa.gov
AF: NOAA Pacific Marine Environmental Laboratory, 7600 Sand Point Way, NE, Seattle, WA 98115 United States
AU: Sabine, C
EM: christopher.l.sabine@noaa.gov
AF: NOAA Pacific Marine Environmental Laboratory, 7600 Sand Point Way, NE, Seattle, WA 98115 United States
AU: Quay, P
EM: pdquay@u.washington.edu
AF: School of Oceanography, box 357940 University of Washington, Seattle, WA 98195
AU: Gammon, R
EM: gammon@u.washington.edu
AF: School of Oceanography, box 357940 University of Washington, Seattle, WA 98195
AB: We reconstruct anthropogenic changes in the $\delta^{13}$C of dissolved inorganic carbon (DI$^{13}$C) in the North Pacific Ocean using a multi-parameter mixing model based on the "novel approach" of Goyet et al. (1999). The approach allows us to use only the recently collected data to estimate the distribution of anthropogenic $\delta^{13}$C. The model computes tracer distributions in the basin by mixing properties of four distinct water types, roughly corresponding to North Pacific Intermediate Water, Subtropical Mode Water, tropical underwaters, and North Pacific Deep Water. Differences between $\delta^{13}$C predicted by the mixing model and measured are assumed to be due to the anthropogenic perturbation, i.e., driven by the atmospheric $\delta^{13}$C decrease since $\sim$1800. The cross-isopycnal penetration of the anthropogenic perturbation within each water type is determined iteratively. The mixing model's $^{13}$C change reconstruction is validated using known anthropogenic tracers such as chlorofluorocarbons and using an ocean general circulation model's simulated $\delta^{13}$C changes. We applied the MIX approach to data collected along WOCE line P13N in 1992. Total (i.e., since the 1800s) anthropogenic DI$^{13}$C changes are detectable to about 1200 meters in the western North Pacific (165$\deg$E). The surface ocean $\delta^{13}$C change in the surface ocean was largest in the subtropical gyre (30$\deg$N), where the $\delta^{13}$C decrease was about 60$%$ of the decrease in the atmosphere. Surface ocean changes were smaller in the tropics (40$%$ of the atmospheric change at 10$\deg$N) and much smaller in the subpolar gyre (only 20$%$ at 50$\deg$N). These century-scale oceanic changes relative to the atmosphere are smaller than observed over the past two decades, suggesting that recent (1970-1990s) decreases in upper-ocean $\delta^{13}$C may be enhanced by possible changes in carbon cycling rates in the North Pacific.
DE: 4805 Biogeochemical cycles (1615)
DE: 4806 Carbon cycling
DE: 4870 Stable isotopes
DE: 1635 Oceans (4203)
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting