Synthesis & Modeling Project
Paul D. Quay
Ann P. McNichol
Oceanic CO2 uptake rates derived from an ocean-wide 13C/12C-DIC data set

NOAA/DOE OACES, 36 months

PROJECT DESCRIPTION: The objective of the proposed research is to use measurements of the 13C/12C of dissolved inorganic carbon (DIC) in the ocean to determine the oceanic uptake rate of anthropogenic produced CO2.  Because of the intensive oceanic sampling for the 13C/12C of the DIC (i.e., DIC13) that occurred during the OACES and WOCE programs in the 1990s there currently exists, for the first time, an ocean-wide high quality DIC13 data set.  This proposal describes a joint effort between the University of Washington and Woods Hole Oceanographic Institution, where DIC13 samples collected during the OACES and WOCE programs were measured, to merge these two data sets which represent 25,000 DIC13 measurements at 1265 stations across all three ocean basins.

The bulk of the proposed work centers on using the merged DIC13 data set to determine the spatial distribution and magnitude of the anthropogenic DIC13 signal and air-sea 13CO2 disequilibrium in the ocean.  Two estimates of the oceanic CO2 uptake rates will be determined by incorporating the ocean-wide estimates of the anthropogenic DIC13 inventory change and air-sea 13CO2 disequilibrium into atmospheric CO2 and 13CO2 budgets.  This effort will improve significantly the previous estimates made, with a much more limited oceanic DIC13 data set, by Quay et al. (1992) and Tans et al. (1993).  A third estimate of the global oceanic CO2 uptake rate will be determined based on the similarity between the oceanic penetration depths of the anthropogenic DIC and DIC13 signals, as described by Heimann and Maier-Reimer (1996).

The oceanic distribution of the anthropogenic DIC13 change will be determined using three approaches.

  1. Comparing depth profiles of DIC13 measured in the 1970s with those measured at nearby locations in the 1990s.  About 25 such sites have been identified.
  2. Calculating the preformed DIC13 distribution along isopycnal surfaces. Preformed DIC13 represents the DIC13 value the water parcel had when it was last at the isopycnal outcrop site.
  3. Using a multiple linear regression to predict the DIC13 measured at a more recent time (1990s) based on the dependence of DIC13 on other ocean parameters measured at an earlier time (1970s).
The anthropogenic DIC13 change represents the difference between the predicted and measured values at the more recent time.  Approaches 2 and 3 are analogous to the approaches used by Gruber et al. (1996) and Wallace (1995), respectively, to reconstruct the anthropogenic DIC signal in the ocean.

We intend to determine the relationship between the anthropogenic DIC13, DIC and bomb 14C signals in the world's ocean. The objectives are twofold. The anthropogenic DIC13 and DIC perturbations in the ocean correlate well based on OGCM predictions (Heimann and Maier-Reimer, 1996). Thus variations of the relative change in the reconstructed anthropogenic DIC13 and DIC perturbations in the ocean provide a useful diagnostic with which to test OGCM predictions of CO2 uptake.  We will examine the relationship between the DIC13 and DIC perturbations via our collaboration with R. Feely (NOAA/PMEL) and colleagues who are proposing to reconstruct the anthropogenic DIC perturbation based on the WOCE and OACES DIC data set.  We will also determine the correlation between the anthropogenic DIC13 and bomb 14C perturbations measured during WOCE via our collaboration with R. Key (Princeton).  An improved correlation between the distributions of the anthropogenic DIC13 change and bomb 14C in the 1990s (vs that observed during GEOSECS in the 1970s) will reduce the error in the 14C-based extrapolation of the ocean-wide anthropogenic DIC13 perturbation. This, in turn, would reduce the error in 13C-derived estimates of oceanic CO2 uptake rates.

DATA: - no data submitted -
PUBLICATIONS: P. Quay. R. Sonnerup, T. Westby, J. Stutsman and A. McNichol (in review) Anthropogenic Changes in the 13C/12C of Dissolved Inorganic Carbon in the Ocean as a Tracer of CO2 Uptake. Global Biogeochemical Cycles. 
RELATED PROJECTS: Thompson; Emerson; Quay "Mechanisms controlling the biological pump and CO2 uptake rates in the North Pacific."

Paul D. Quay
School of Oceanography
University of Washington
P.O. Box 357940
Seattle, WA 98195
tel: (206) 685-8061
fax: (206) 685-3351

Ann P. McNichol
National Ocean Sciences AMS Facility
Woods Hole Oceanographic Institution
McLean Laboratory, Mail Stop #8
360 Woods Hole Road
Woods Hole, MA 02543-1539
tel: (508) 289-3394
fax: (508) 457-2183
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