HR: 0830h
AN: OS31C-0219    [PDF]
TI: The $\delta$$^{18}$O of Dissolved O$_{2}$: Implications for Ocean Respiration and Circulation
AU: * Levine, N M
EM: nlevine@princeton.edu
AF: Department of Geosciences, Princeton University, Guyot Hall, Washington Rd., Princeton, NJ 08544 United States
AU: Dunne, J P
EM: John.Dunne@noaa.gov
AF: AOS Program, Princeton University, NOAA/Geophysical Fluid Dynamics Laboratory Forrestal Campus, Princeton, NJ 08542 United States
AU: Kiddon, J A
EM: kiddon.john@epa.gov
AF: USEPA Environmental Effects Research Laboratory, Atlantic Ecology Division/ORD 27 Tarzwell Drive, Narragansett, RI 02882 United States
AU: Bender, M L
EM: bender@princeton.edu
AF: Department of Geosciences, Princeton University, Guyot Hall, Washington Rd., Princeton, NJ 08544 United States
AB: The $\delta$$^{18}$O of dissolved O$_{2}$ of aphotic waters has been shown to be a tracer of both ocean circulation and oxygen consumption by respiration. Here we present $\delta$$^{18}$O of O$_{2}$ data for samples from the South Atlantic Ventilation Experiment(SAVE) in a zonal section along $\sim$15$\deg$S. Our samples are concentrated in the main thermocline including the strong oxygen minimum off the coast of Africa. The data significantly extend the existing dataset of deep ocean $\delta$$^{18}$O of O$_{2}$. We interpret the data with two models of varying complexity. Because of isotope fractionation during respiration, $\delta$$^{18}$O rises as [O$_{2}$]/[O$_{2}$]$_{sat}$ falls. As elsewhere, the $\delta$$^{18}$O increase in the SAVE samples is far less than predicted for Rayleigh (closed system) fractionation. A one-dimensional isopycnal diffusion-reaction model successfully simulates the SAVE $\delta$$^{18}$O data using reasonable values for the ratio of O$_{2}$ consumption to horizontal eddy diffusion, and for the respiratory isotope fractionation. This model provides a good fit to the South Atlantic data using an isotope fractionation factor between 0.980 and 0.985 and a range of -2x10$^{-5}$ to -2x10$^{-6}$mmol/m$^{3}$/km$^{2}$ for the ratio of consumption to isopycnal diffusion. These results agree with the conclusions of previous studies. The Geophysical Fluid Dynamics Laboratory general circulation model MOM3 was modified to include the tracer $^{18}$O$^{16}$O. The model successfully simulated the observed relationship between $\delta$$^{18}$O and oxygen saturation for the SAVE samples. The model thus adequately represents the interaction between respiration rates and mixing as expressed by $\delta$$^{18}$O of O$_{2}$ in our study region.
DE: 4808 Chemical tracers
DE: 4842 Modeling
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting