Hydrothermal ³He and manganese plumes at 19°29′S on the Central Indian Ridge

Abstract

We report the discovery of a hydrothermal helium‐3 plume north of the Indian Triple Junction, on the Central Indian Ridge at 19°29′S. Water column δ 3 He anomalies show a spike of 33.8% at 2460 meter depth, i.e. the highest δ 3 He anomaly recorded so far in the Indian ocean. The helium‐3 data are correlated with manganese, giving a Mn/ 3 He ratio of 700 mol/cm 3 (3.8×10 4 g/cm 3 STP). The CH 4 / 3 He ratio deduced from available CH 4 /Mn data in the same area is around 7×10 6 . These values are close to what is observed on water column plumes on the East Pacific Rise. On a regional scale, the 3 He distribution over the Indian Triple Junction exhibits a strong δ 3 He increase at the Ridge crest, which appears to spread eastwards through the deep Indian ocean.