Noble gas signals in corals predict submarine volcanic eruptions

Deep-water corals growing in close proximity to the 2011 submarine eruption at Tagoro (El Hierro Island; Canary Archipielago, Spain) have revealed their ability to record the magmatic helium (³He) signal during a period of months prior to the eruption with magmatic ³He/⁴He ratios of 3.6–5.0 R_A This is similar to the range of He isotope values (3–10 Ra) obtained from olivine samples from basinites erupted during the 2011 Tagoro eruption. Whip-like black corals (Anthozoa: Antipatharia: Antipathidae: Stichopathes) growing on basaltic rocks trapped 3He within their skeletons. We used a theoretical growth rate to estimate the time of trapping of ³He between release from the magmatic source at depth to trapping by the aquatic organisms. Our findings suggest that magmatic 3He emission occurred a few months before the beginning of the seismic activity in the region, the latter occurring four months in advance of the beginning of the eruption. This discovery implies that corals living in submarine volcanic areas may act as archives of noble gases released before the beginning of an eruption, and that the continuous monitoring of ³He may help to constrain the arrival time of a subaqueous eruption with potential applications in volcano eruption forecasting.