HE-3 AND METHANE IN THE GULF OF ADEN

During the OCEAT cruise (July, 1987), the vertical and spatial distributions of 3He and methane were measured at six stations over the West Sheba Ridge (Gulf of Aden). The results show significant δ3He anomalies (up to 49%). We conclude that the origin of this signal is independent from the well-known Red Sea hydrothermal 3He (of Red Sea Brines). Thus, active hydrothermalism occurs in this extensional basin associated with spreading along an incipient mid-ocean ridge. The 3He input from the Gulf of Aden accounts for the S-N positive gradient in 3He concentration observed in the western part of the Indian Ocean. Several methane anomalies are also present (up to 664 nl/l, i.e., 25 times the regional methane background), but the CH4 and 3He signals are not systematically correlated, suggesting complex production and consumption mechanisms of methane in these areas. Our results confirm previous observations in the South West Pacific Ocean. © 1990.