Water-column geochemical anomalies associated with the remnants of a mega plume: A case study after CR-2003 hydrothermal event in Carlsberg Ridge, NW Indian Ocean

Recently, an unusually large hydrothermal event (CR-2003) was reported over the slow-spreading Carlsberg Ridge between 05°41'N, 61°30'E and 06°20'N, 60°33'E. To investigate the after effects (if any) of such a large-scale emission, almost a year later in July 2004, the water column along the 50 km ridge segment was surveyed. Results show that while the thermal and optical signatures have largely reduced with time, the chemical signatures do persist between 2500 and 2900 m. Geochemical features like Fe/Mn, Mn/heat ratios, characteristic of event plume, also show major changes. Distribution of dissolved manganese, methane, helium-3 and suspended particulates further down the water column was indicative of one more plume layer between 3150 and 3400 m. The high volatile and less particulate metal content of the deep layer points towards a relatively fresh event.