GLOBAL EMISSIONS OF HE-3 BY SUBAERIAL VOLCANISM

The emission rate of helium-3 by subaerial volcanism is re-evaluated by coupling He-3/CO2 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 He-3/yr, most of which is due to non-arc volcanoes. Major eruptions represent minor additions on average, whereas diffuse He-3 emanations through volcanic piles may be important sources. Although not including this contribution, the above figure is equivalent to 20-40% of the He-3 flux from mid-ocean ridges and, thus, suggests that primordial He-3 degassing from subaerial volcanic regions may be larger than expected.