Principal Investigator: Rik Wanninkhof
Collaborating scientist(s):
Hua Chen (CIMAS)
Esa Peltola
Objective: Measurement of the partial pressure of CO2 in subsurface samples (discrete pCO2) in order to determine the anthropogenic CO2 input and to characterize water masses.
Rationale: In order to fully understand the oceanic inorganic carbon cycle, and in specific to separate the anthropogenic CO2 invasion from the biogeochemical cycling of carbon, at least two of the four carbon system parameters (total dissolved inorganic carbon (DIC), total Alkalinity (TAlk), pCO2, and pH) must be measured. pCO2 has the largest dynamic range of the four parameters and is an excellent parameter to use in calculations.
Method: An aliquot of water is equilibrated with a headspace of known CO2 concentration. After equilibration the headspace gas is analyzed using a standardized infra-red analyzer or gas chromatograph. (Wanninkhof and Thoning, 1993)
Description: Oceanic CO2 increases caused by anthropogenic invasion will manifest itself by increases in pCO2 and DIC while TAlk remains constant. To the contrary, increases caused by respiration will cause DIC, pCO2 and TAlk to increase. The large dynamic signal of discrete pCO2 from 200 microatmosphere at the surface to 2000 microatmosphere in thermocline waters (Figure 1) and good precision (<0.5 % of full signal) of the measurement make it an ideal parameter to measure. As part of the OACES base line long lines effort the measurements are performed in each ocean basin. Since pCO2 will increase ten times faster than DIC due to anthropogenic invasion we expect a large change in this property when repeat occupations are performed five to ten years after the initial occupation.
Key reference:
Chen, H., R. Wanninkhof, R.A. Feely, and D. Greeley, Measurement of fugacity of carbon dioxide in sub-surface water: an evaluation of a method based on infrared analysis, NOAA Technical Memorandum ERL AOML-85, 1995.

Wanninkhof, R., and K. Thoning, Measurement of fugacity of CO2 in surface water using continuous and discrete sampling methods, Mar. Chem., 44 (2-4), pp. 189-205, 1993.

Wanninkhof R. and Feely R.A. (1998) fCO2 dynamics in the Atlantic, Pacific, and South Indian Ocean. Marine Chemistry accepted "CO2 in the Oceans, special issue".

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