Twenty years after the discovery of sea-floor hot springs, vast stretches of the global mid-ocean-ridge system remain unexplored for hydrothermal venting. The southwest Indian ridge is a particularly intriguing region, as it is both the slowest-spreading of the main ridges and the sole modern migration pathway between the diverse vent fauna of the Atlantic and Pacific oceans. A recent model postulates that a linear relation exists between vent frequency and spreading rate and predicts vent fields to be scarcest along the slowest-spreading ridge sections, thus impeding migration and enhancing faunal diversity. Here, however, we report evidence of hydrothermal plumes at six locations within two 200-km-long sections of the southwest Indian ridge indicating a higher frequency of venting than expected. These results suggest 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-flow between Pacific and Atlantic hydrothermal fields.
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