The presence of 3He in excess of its saturation in the deep ocean is an unmistakable sign for exchange between water and material of magmatic origin. For example, in locations such as the Galapagos Spreading Center or the Red Sea, substantial excesses of this isotope bear witness to present and past hydrothermal activity at the seafloor [Jenkins 1978; Lupton et al., 1977]. Our measurements of 3He in the Black Sea in 1988 show that there is about 13% excess of this isotope in the water column of the southern half of the basin with indications that its injection may be occurring along the southern coast. This must be related to tectonic activity, also observed to be happening along the south coast.
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