The carbon isotope content of dissolved inorganic carbon was measured for large cold springs in the central Oregon Cascades. Low 14C activities in some of the springs are interpreted to result from the dissolution of diffuse emissions of magmatic CO2, even though volcanic activity has not occurred in this area for more than 1300 yr. On the basis of dissolved magmatic carbon concentrations in the springs, we infer a diffuse magmatic CO2 degassing rate of 3.4 × 105 kg/yr per kilometer of arc for the central Oregon Cascades. The CO2 flux calculated from estimates of the mean magmatic intrusion rate and experimentally determined values of CO2 content in melts is consistent with that determined from our measurements of the dissolved CO2 flux at springs.

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