Principal Investigator: Rik Wanninkhof
Collaborating scientist(s):
Tom Lantry up to 4/96
Bob Castle
Esa Peltola
Objective: Measurement of the total dissolved inorganic carbon (DIC) to determine oceanic carbon inventory and changes with time
Rationale: DIC, which is the sum of gaseous CO2, bicarbonate and carbonate is the major carbon reservoir in the ocean. Invasion of anthropogenic CO2 should change the DIC inventory. However, up until now direct observation has been problematic because of a small signal against a large background. A 40% oceanic uptake will correspond to average change in DIC of 1 micromol kg-1 year-1 in the upper ocean while the DIC concentration ranges from 1800 to 2300 micromol kg-1. These uptake estimates are based on observations of the fraction of fossil fuel carbon remaining in the atmosphere and the penetration of bomb 14C into the upper ocean. However, to increase our confidence in this value direct observations are essential. The OACES program aims at determining the change in oceanic DIC by occupying repeat long lines transects in every ocean basin on five to ten-year time scales.
Method: Measurements are performed using a coulometer attached to a SOMMA inlet system developed by Ken Johnson at Brookhaven National Lab.
Accomplishment: Using state-of-the-art instrumentation and certified reference materials calibrated independently in a land based laboratory, precisions and accuracies of better than 1.5 micromol kg-1 have been obtained on cruises to date in the Atlantic, Pacific and Indian Oceans. Robust estimates will involve detecting a small signal in a system which sees seasonal and lateral variations of over 200 micromol kg-1 due to consumption by photosynthesis at the surface and respiration below, and transport by currents (Figure 1). The biological signal can be separated from the anthropogenic signal using other carbon system parameters, and by use of transient tracers.
Key reference:
Lantry, T., M.F. Lamb, J.C. Hendee, R. Wanninkhof, R.A. Feely, F.J. Millero, R. Byrne, E.T. Peltzer, D. Wilson, and G. Berberian, Chemical and hydrographic measurements from the Equatorial Pacific during boreal spring 1992, NOAA Data Report ERL AOML-27, 1995.

Forde, E.B., J.C. Hendee, and R. Wanninkhof, Hydrographic, carbon dioxide, nutrient, and productivity measurements from the South Atlantic during July and August of 1991, NOAA Data Report ERL AOML-24, 1994.

Castle R., Wanninkhof R.,Doney S. C., Bullister J., Johns L., Feely R.A., Huss B. E., Millero F. J., and Lee K. (submitted, 1998) Chemical and hydrographic profiles and underway measurements from the North Atlantic during July and August of 1993, NOAA data report ERL AOML-XX. NOAA/ERL/AOML.

Click here to return to the AOML project overview page.
Click here to return to the Predict & Assess Decadal to Centennial Change page.

Page last modified: .
Please direct any questions or comments to the OCD Webmaster.