Excess 3He in the sea: evidence for terrestrial primordial helium

We have found a large enrichment of ³He in deep Pacific water, relative to the atmospheric ³He/ ⁴He ratio. A sample from 1737 m shows 21.8 ± 2.1% excess ³He, and deeper samples range from 5.8 ± 1.9% to 12.2 ± 2.0%, whereas a surface sample and one from 866 m show identical ³He/ ⁴He as compared to air within experimental error. We have also measured total helium contents and find excess amounts of -3 ± 3% to 8 ± 3% relative to solubility data. The results for total helium are in agreement with recent work of Bieri, Koide and Goldberg, and our previous measurement from Carrousel Expedition. There appears to be a rough correlation between ³He excess and ⁴He excess indicating that there are two components in varying proportions, one with an atmospheric ³He/ ⁴He ratio, and another with a considerably higher ratio. We conclude that the excess ³He is due to leakage into ocean water of a remnant of the earth's primodal ³He — there appears to be no other possible mechanism. The effects we see could be accounted for by a leak rate of about 2 atoms cm ^-2 sec ^-1, a value of the order of the amount required to balance the difference between the production rate of ³He from various other sources and the escape rate by thermal and non-thermal processes.