Global emissions of helium‐3 by subaerial volcanism

The emission rate of helium‐3 by subaerial volcanism is re‐evaluated by coupling 3 He/CO 2 ratios in volcanic gases with new estimate of the flux of carbon dioxide from both arc and non‐arc volcanoes. Steady volcanic plume emissions are computed to supply 240–310 mole 3 He/yr, most of which is due to non‐arc volcanoes. Major eruptions represent minor additions on average, whereas diffuse 3 He emanations through volcanic piles may be important sources. Although not including this contribution, the above figure is equivalent to 20–40% of the 3 He flux from mid‐ocean ridges and, thus, suggests that primordial 3 He degassing from subaerial volcanic regions may be larger than expected.