HYDROTHERMAL ANOMALIES IN THE LUCKY-STRIKE SEGMENT ON THE MID-ATLANTIC RIDGE (37-DEGREES-17'N)

As part of the FARA (French-American Ridge Atlantic) project the north ern Mid-Atlantic Ridge (MAR) was surveyed for hydrothermal activity be tween 33 degrees and 40 degrees N during the FAZAR cruise in August-Oc tober 1992. After detection of hydrothermal activity in the Lucky Stri ke segment (37 degrees 17'N) a detailed water column survey was undert aken in this region, During a follow-up cruise (with the DSRV ALVIN) s everal active high-temperature vents were found on the summit of an ce ntral seamount. Here we focus on the results of the water column surve y undertaken during the FAZAR cruise. The influence of Mediterranean w ater and the site's shallow depth complicates the hydrography at Lucky Strike; background temperature and salinity gradients are usually too complex to indicate hydrothermal anomalies clearly. Light transmissio n anomalies within the Lucky Strike region were small, but were detect ed throughout the segment from mid-depth (similar to 1500 m) all the w ay to the valley seafloor (similar to 2300 m depth). The large depth r ange covered by these anomalies probably results from vertical mixing as well as the presence of multiple vent sources at various depths. Me thane anomalies and a temperature anomaly observed deeper than the ven ts documented by ALVIN further support the idea of additional, deeper vents within this segment. Particle samples of the deep particle layer are enriched in Fe and trace metals.