Elevated turbidity and dissolved manganese in deep water column near 10�47�S Central Indian Ridge: studies on hydrothermal activities

Abstract

The deep water in the ridge segment between 10°18'S and 10°57'S of northern Central Indian Ridge was surveyed with CTD and AUV for seafloor hydrothermal activities. During the survey, 25 CTD hydrocasts were made, and seawater samples were collected for analyses of chemical tracers like dissolved manganese (DMn). In the rift valley between 10°40'S and 10°57'S, consistent backscatter anomalies (up to 0.013 deltaNTU) were found in deep water, indicating excess of suspended particulate at the depth between 3050 and 3500 m. The seawater samples from this turbid layer was characterized with high concentration of dissolved manganese (maximum DMn = 39nmol/L) and excess helium-3 (maximum deltaδ3He = 17.1%) and thus confirmed the possible hydrothermal activities in that area. The distribution of turbidity and DMn in deep water apparently suggests that there could be active vent(s) located close to the eastern wall (10°47.5'S; 66°38.6'E) of the valley, near southern end of the ridge segment. The physiochemical characters of the plume suggest the source fluid might have originated from reactions involving both mafic and ultramafic rocks, and its nature is comparable to other plumes in the Indian Ocean.