CO2 emissions related to the Yellowstone volcanic system 2. Statistical sampling, total degassing, and transport mechanisms

A stratified adaptive sampling plan was designed to estimate CO2 degassing in Yellowstone National Park and was applied in the Mud Volcano thermal are a. The stratified component of the sampling design focused effort in therma l areas and the adaptive component in high-flux regions, yet neither sampli ng technique biased the estimate of total degassing. Both diffuse soil flux es (up to similar to 30,000 g m(-2) d(-1)) and emission rates from thermal vents (up to 1.7 x 10(8) mol yr(-1)) were measured in thermal areas. Soil f luxes observed in most nonthermal regions were similar to values reported f or conifer forests (less than or equal to 15 g m(-2) d(-1)). However, throu gh adaptive sampling, high-flux vegetated sites were identified in Mud Volc ano that likely would not have been found if sampling was focused in obviou s thermal or altered regions. A simple model applied to flux measurements s uggests that similar to 40% of the analyzed measurements were dominated by possible advective transport and similar to 30% by diffusive transport. Iso topic signatures of soil CO2 generally suggest a deep origin (delta(13)C = -2.3 to 0.0) in thermal areas and biogenic origin (delta(13)C = -20.5) in n onthermal, low-flux areas. Vent emissions accounted for similar to 32-63% o f the total degassing observed at Mud Volcano (2.4 to 4.0 x 10(9) mol yr(-1 )). The largest source of error in the estimation of total degassing (facto r of similar to 2) resulted because the population distribution of thermal feature emissions was indeterminate. Total CO2 emissions at Mud Volcano are comparable to other hydrothermal regions worldwide, suggesting that the Ye llowstone volcanic system is likely a large contributor to global volcanic/ metamorphic/hydrothermal (VMH) emissions.