Time rate of atmospheric 3He/4He change: Constraint from South Pacific deep seawater

Sano Yuji

Journal of science of the Hiroshima University. Series C, Earth and planetary sciences

A recent study of atmospheric 3He/4He ratio has suggested that it is decreasing with time, perhaps due to anthropogenic release from oil and natural gas wells of crustal helium with a low 3He/4He ratio. A couple of objections have been made against this hypothesis based on new observations. It is important to verify the time rate of atmospheric 3He/4He change, since this has serious implications for the field of helium isotope geochemistry. I present here the time rate change of -0.094±0.156 %/year (2σ errors) based on the 3He/4He ratio obtained from South Pacific deep seawater. Taking into account four other independent measurements on the time rate, I can calculate the average time rate of -0.028±0.030 %/year (2σ), which is consistent with a zero rate of change in atmospheric 3He/4He ratio. However the average time rate is also consistent with the time rate of -0.033 %/year estimated from anthropogenic release of crustal helium. Thus the problem is not yet solved and further study is desirable.

eng

Hiroshima University

[ISSN] 0075-4374

[NCID] AA11095875