MEASUREMENT OF UNDERWAY PCO2

Principal Investigator: Rik Wanninkhof
Collaborating scientist(s):
Matt Steckley 8/92 through 4/94
David Ho (CIMAS) up to 8/95
Jason Masters (NOAA corps) from 2/96
Robert Castle from 3/97
Survey department of NOAA Ship Ronald Brown and Ka'imimoana
Objective: Measurements of the partial pressure difference of CO<2 (pCO)2 in order to determine regional and global air-sea CO2 fluxes
Rationale: The air-sea flux of CO2 (F) is commonly determined from the gas transfer velocity multiplied the partial pressure difference across the air-water interface:
F= kDpCO2
By measuring DpCO<2 with automated systems on ships of opportunity a global flux map can be produced.
Method: Since 1991, a semi-automated system on the NOAA ship MALCOLM BALDRIGE measures the pCO2 in air and water on all research cruises in order to fill critical voids in the global data set of D pCO2measurements. In 1997 underway equipment was set up on the new NOAA ship RONALD BROWN.
Underway pCO2 data has been collected since 1991 on various ships and the extent of global coverage can be seen from TOTAL_UNDERWAY_TRACKLINES.
Accomplishment: The area of concentrated deployment has been the equatorial Pacific where, in conjunction with a similar effort on NOAA Ship DISCOVERER and Ka'imimoana lead by Dr. Feely of PMEL, seasonal snapshots of surface water CO2 levels have been obtained (Figure 1). The results show that the 1992 El Niņo depressed the sea to air flux of CO2 by about 1/2 from 0.8 Gigaton C/yr to 0.3 Gigaton C/yr. Surface pCO2 levels did not return back to normal until 1994 due to the prolonged positive sea surface temperature anomaly.
Key references:
Ho D. T., Wanninkhof R., Masters J., Feely R. A., and Cosca C.E. (1997) measurement of underway fCO2 in the Eastern Equatorial Pacific on NOAA ships BALDRIDGE and DISCOVERER, NOAA data report ERL AOML-30, 52 pp.

Masters J., Wanninkhof R., Ho D., Steckley M., Feely R., and Cosca C. (1997) Continuous air and surface seawater measurements of fCO2 on board the NOAA ship MALCOLM BALDRIGE around the world cruise in 1995, NOAA data report ERL AOML-31 pp. 65. NOAA/AOML/ERL.

Takahashi T., Feely R. A., Weiss R., Wanninkhof R., Chipman D. W., Sutherland S. C., and Takahashi T. T. (1997) Global air-sea flux of CO2: An estimate based on measurements of sea-air pCO2 difference. Proc. Natl. Acad. Sci. USA 94, 8292-829 9.

Wanninkhof, R., R.A. Feely, D.K. Atwood, G.A. Berberian, W.D. Wilson, P.P. Murphy, and M.F. Lamb, Seasonal and lateral variations in carbon chemistry of surface water in the eastern equatorial Pacific during 1992, Deep-Sea Res., 42, pp. 387-410, 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., R.A. Feely, H. Chen, C. Cosca, and P. Murphy, Surface water fCO2 in the Eastern Equatorial Pacific during the 1992-93 El Niņo, J. Geophys. Res., 101, pp. 16333-16343, 1996.

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