HYDROTHERMAL ACTIVITY ALONG THE SOUTHWEST INDIAN RIDGE

Twenty years after the discovery of sea-floor hot springs, vast stretc hes of the global mid-ocean-ridge system remain unexplored for hydroth ermal venting, The southwest Indian ridge is a particularly intriguing , region, as it is both the slowest-spreading of the main ridges(1) an d the sole modern migration pathway between the diverse vent fauna of the Atlantic and Pacific oceans(2). A recent model postulates that a l inear relation exists between vent frequency and spreading rate(3) and predicts vent fields to be scarcest along the slowest-spreading ridge sections, thus impeding migration and enhancing faunal diversity(2). Here, however, we report evidence of hydrothermal plumes at six locati ons within two 200-km-long sections of the southwest Indian ridge indi cating: a higher frequency of venting than expected. These results sug gest that fluxes of heat and chemicals from slow-spreading ridges may be greater than previously thought and that faunal migration along the southwest Indian ridge may serve as an important corridor for gene-fl ow between Pacific and Atlantic hydrothermal fields.