Hydrothermal anomalies in the Lucky Strike segment on the Mid-Atlantic Ridge (37°17′N)

As part of the FARA (French-American Ridge Atlantic) project the northern Mid-Atlantic Ridge (MAR) was surveyed for hydrothermal activity between 33° and 40°N during the FAZAR cruise in August–October 1992. After detection of hydrothermal activity in the Lucky Strike segment (37°17′N) a detailed water column survey was undertaken in this region. During a follow-up cruise (with the DSRV ALVIN) several active high-temperature vents were found on the summit of an central seamount. Here we focus on the results of the water column survey undertaken during the FAZAR cruise. The influence of Mediterranean water 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 transmission anomalies within the Lucky Strike region were small, but were detected throughout the segment from mid-depth (∼ 1500 m) all the way to the valley seafloor (∼ 2300 m depth). The large depth range covered by these anomalies probably results from vertical mixing as well as the presence of multiple vent sources at various depths. Methane anomalies and a temperature anomaly observed deeper than the vents 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.