DETECTION OF HYDROTHERMAL PLUMES ALONG THE SOUTHEAST INDIAN RIDGE NEAR THE AMSTERDAM-ST-PAUL PLATEAU

A new self-contained profiling instrument, attached to 91 lowerings of waxcores and dredges along a 1600 km stretch of the Southeast Indian Ridge, found six sites having optical back-scatter anomalies indicativ e of hydrothermal plumes from high-temperature seafloor venting. At fi ve other sites, back-scatter anomalies were less distinct, and at the remaining sites, anomalies were absent. These are the first documented hydrothermal sites along this intermediate-rate spreading center and are among the very few yet discovered in the Indian Ocean basin. Some profiles complex back-scatter anomalies suggestive of sources of seafl oor discharge. At one site, near bottom temperature anomalies of simil ar to 0.1 degrees C and the recovery of a vent-specific barnacle provi de the first precise seafloor location of active venting in the deep I ndian Ocean. Although this study is only reconnaissance in nature, ven ting along this portion of the SEIR appears to be significantly less t han predicted by global correlations of plume incidence as a function of spreading rate. Nevertheless, these sites may be important as biolo gical connections between distinct faunal assemblages of Atlantic and Pacific vent fields.