The distribution of 3He in the western Atlantic ocean

Over 250 samples of Atlantic seawater have been analyzed for the dissolved helium isotopes, and distinctive pattern has emerged. Two components of excess ³He are seen: a component due to in situ decay of nuclear-era tritium, and a primordial component evolved from the solid Earth. A prominent feature at about 3-km depth can be traced from 5°N along the western boundary to the equator. The source of this feature is most probably in the Gibbs fracture zone, where we suppose that primordial ³He is released into westward-flowing bottom water. The South Atlantic profiles clearly show the effect of ³He-rich CCircumpolar Water, entrained by Antarctic Intermediate Water flowing northward. The excess ³He in the upper 1 km, when combined with tritum concentrations measured byO¨stlund, Dorsey and Rooth (1974, Earth and Planetary Science Letters, 23, 69–86) at the same locations and depths, yields ‘tritium-helium ages’, which in some cases represent the time interval between equilibration wwith the atmosphere and sampling.