Variation of CO2 Partial Pressure in Surface Seawater
in the Equatorial Pacific Ocean

Catherine Goyet and Edward T. Peltzer*
Marine Chemistry and Geochemistry Department
Woods Hole Oceanographic Institution
Woods Hole, MA 02543

Deep-Sea Research I (1997) 44: 1611-1625.

Received: 1 April 1996.
Revised: 16 October 1996.
Accepted: 14 March 1997.
Published: October 1997.

*: Present address: Monterey Bay Aquarium Research Institute
PO Box 628, Moss Landing, CA 95039-0628, USA.


The partial pressure of CO2 gas in seawater [pCO2(sea)] and in the atmosphere [pCO2(air)] was continually measured in the equatorial Pacific Ocean during two US JGOFS cruises in 1992. Time-series measurements at the equator and 140°W show that the pCO2 of surface seawater varied by 30 µatm during the 2 week period of the experiment with a diurnal variation close to 8 µatm. The diurnal variations of pCO2(sea) on a weekly time-scale was associated with water movements (equatorial upwelling and passage of a tropical instability wave) rather than heating or cooling of surface water. The water movements are characterized by change in temperature as well as salinity, total inorganic carbon and total alkalinity. During the upwelling period, pCO2(sea) increased whereas sea surface temperature decreased. From the equator to 13°S, pCO2(sea) decreased from 430 µatm to 340 µatm whereas the sea surface temperature increased from 25.4°C to 28.3°C. However, there was no overall correlation between pCO2(sea) and sea surface temperature. Indeed, the pCO2(sea) varied irregularly with temperature across a complex system of fronts and eddies. The observed diurnal variations of pCO2(sea) while the ship was in transit between Tahiti and the equator were up to 8 µatm.


This research was supported by the National Science Foundation via grants OCE-9115317 to CG and OCE-9115201 to ETP. Computers for data processing were supported by NASA EOS Interdisciplinary Science program grant NAGW-2431. We thank program managers N. Andersen and G. Asrar.

The authors gratefully acknowledge the captain, crew and technicians of the R/V Thomas G. Thompson for their help and support. We thank S. Kadar for logistic support. We thank chief scientists J. W. Murray, M. Bacon and R. T. Barber for cruise planning and leadership. We thank R. McDuff and G. White for providing copies of the ship's weather log with wind and air temperature data.

This paper is contribution no. 9210 from the Woods Hole Oceanographic Institution, and US-JGOFS contribution no. 347.

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