Ann McNichol

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Senior Research Specialist
Geology & Geophysics

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Ann McNichol, the staff chemist and director of the sample-preparation laboratory, is studying the distribution of 13C in oceanic DIC in order to understand the ocean’s role in the uptake of fossil-fuel-derived CO2 and to examine other processes in the carbon cycle. Her work follows earlier examinations of the fate of anthropogenic CO2 in the oceans (Quay et al., 1992; Heimann and Maier-Reimer, 1996; Tans et al., 1993) and updates them through use of the extensive data set of δ13C values collected during the analyses of the WOCE samples at NOSAMS.

Research Overview
With support from NOAA, McNichol and Dr. Paul Quay (University of Washington, Seattle) have combined the NOSAMS and UW data sets (approximately 12,500 points each) in order to produce the first global ocean atlas of high-quality δ13C-DIC measurements. The data have been deposited in both the WOCE and JGOFS databases. In addition, Quay and McNichol are using the data to investigate the ocean carbon cycle. To date most of the work has focused on re-assessing the magnitude of the uptake of fossil fuel CO2 (Sonnerup et al., 1999; Sonnerup et al., 2000; Quay et al., 2002). Efforts to quantify the fossil fuel uptake are hampered by the lack of good historical data. The new δ13C data set shows that not only are the Pacific GEOSECS δ13C data problematic, but also that another 1970's data set has a significant offset (0.15-0.2‰) that makes its usefulness questionable (Lerperger et al., 2000).

Dr. Rolf Sonnerup (PMEL) and McNichol have recently been funded to apply a new approach to evaluating the uptake of CO2. They will extend and modify the "novel approach" used by Goyet et al. (1999) to analyze DIC data and will use the new δ13C database to calculate the anthropogenic uptake of CO2 by the ocean. In the approach, the entire water column will essentially be “unmixed” using an optimized, multiparameter mixing model, a functional relationship between the uptake of CO2 and 13C will be assumed, and an expected (i. e., unperturbed) distribution will be calculated. Comparing this to the observed (i. e., perturbed) distribution will allow an estimate of the amount of CO2 added to the ocean.

Heimann M. and Maier-Reimer E. (1996) On the relations between the oceanic uptake of CO2 and its carbon isotopes. Glob. Biogeochem. Cycl. 10, 89-110.

Lerperger M., McNichol A.P., Peden J., Gagnon A.R., Elder K.L., Kutschera W., Rom W. and Steir P. (2000) Oceanic uptake of CO2 re-estimated through delta C-13 in WOCE samples. Nucl. Inst. Meth. Phys. Res. B 172, 501-512.

Quay P.D., Tilbrook B. and Wong C.S. (1992) Oceanic uptake of fossil fuel CO2: Carbon-13 evidence. Science 256, 74-79.

Sonnerup R.E., Quay P.D., McNichol A.P., Bullister J.L., Westby T.A. and Anderson H.L. (1999) Reconstructing the oceanic 13C Suess effect. Glob. Biogeochem. Cycl. 13, 857-872.

Sonnerup R.E., Quay P.D. and McNichol A.P. (2000) The Indian Ocean 13C Suess effect. Glob. Biogeochem. Cycl. 14, 903-916.

Tans P.O., Berry J.A. and Keeling R.F. (1993) Oceanic 13C/12C observations: a new window on ocean CO2 uptake. Glob. Biogeochem. Cycl. 7, 353-368.

Last updated: March 9, 2020