THE RAINBOW HYDROTHERMAL PLUME, 36-DEGREES-15'N, MAR

The Rainbow hydrothermal plume was discovered during a recent geophysi cal survey along 200km of the Mid-Atlantic Ridge (MAR), SW of the Azor es Triple Junction, in which at least seven new sites of hydrothermal activity were identified. Here, we present the first hydrographic stud y of the Rainbow plume, 36 degrees 15'N, the strongest of the features located during that survey. The plume is detectable from real-time in situ nephelometer anomalies and extends 10-15km, W-E, in a non-transf orm discontinuity (NTD) between two adjacent ridge-segments. Maximum a nomalies in the Rainbow plume indicate particle enrichments at least a s large as those seen directly above the Trans Atlantic Geotraverse (T AG) vent-field (26 degrees N, MAR). Analysis of hydrographic data indi cates a vent source at Rainbow with a thermal output of up to 98 MW, r epresenting 140% of the thermal output previously attributed to TAG. B oth lines of evidence indicate the Rainbow plume to be the strongest s uch feature yet found on the MAR.