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Atmospheric CO2 from Flask Air Samples at Cape Matatula, American Samoa

graphics Graphics   data Data

C.D. Keeling and T.P. Whorf

Carbon Dioxide Research Group, Scripps Institution of Oceanography, University of California, La Jolla, California 92093-0444, U.S.A.

Period of Record



Atmospheric CO2 samples were collected at approximately weekly intervals. Samples are collected in 5-L evacuated glass flasks, and then returned to the Scripps Institution of Oceanography (SIO) where CO2 concentrations have been determined using an Applied Physics Corporation (APC) nondispersive infrared gas analyzer. Further information on measurements, calibration procedures and analysis is available in the references listed below.

Map showing location of American Samoa (Cape Matatula), U.S. Territory

American Samoa (Cape Matatula), U.S. Territory,
Pacific Ocean rocky costal promontory
14°15' S, 170°34' W
30 m above MSL


The average of unflagged data for the first full year of measurements (1982) was 340.6 ppmv; values for 2001 averaged 369.8 ppmv, for an upward trend of 1.54 ppmv/year. Graphics here show the first and last year of data, to display the change in mean over time and the annual patterns. Long term trend curves are better displayed using the SIO's PDF monthly averaged data. The annual pattern of CO2 at American Samoa is unlike that for other stations. It does not have a single, clearly defined peak during the late winter months. This is because the air arriving at American Samoa does not come from a single dominant source, but rather from diverse sources in both hemispheres, and possibly includes air that has been "circulating around" within the tropics for as much as a month or more before arriving at the sampling location. For more information, see Manning et al., 2003.


CITE AS: Keeling, C.D. and T.P. Whorf. 2004. Atmospheric CO2 concentrations derived from flask air samples at sites in the SIO network. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, U.S.A.