³He in the Bransfield Strait waters: indication for local injection from back-arc rifting

Helium data from the waters of the Bransfield Strait, the southern Drake Passage and the northwestern shelf of the Weddell Sea are presented. The ³He profiles from the eastern and central basins of the Bransfield Strait show maxima (δ³He ≈ 7%) below the sill depths that separate the strait from the surrounding open ocean. The ³He excess is interpreted as a local injection of a ³He-rich helium component into the deep waters of the Bransfield Strait from backarc rifting. Tritiogenic ³He and excess ³He from mixing with Circumpolar Deep Water are excluded as possible sources. The estimated ³He/⁴He ratio of the injected helium component (2.4-5.0 × 10^-6) is less than that of pure mantle helium and may contain radiogenic helium from continental crustal material which underlies the Bransfield Strait.