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1 Department of Earth Sciences, Cambridge University, Downing Street, Cambridge CB2 3EQ, UK
2 Institute of Oceanographic Sciences, Wormley GU5 8UB, UK
3 Department of Geology, University of Bristol, Bristol BS8 1RJ, UK
4 College of Oceanography, Oregon State University, Corvallis, OR 97331, USA
5 P.P. Shirshov Institute of Oceanology, Moscow 117218, Russia
6 Department of Oceanography, University of Southampton, Highfield, Southampton SO9 5NH, UK
Two distinct hydrothermal plumes have been identified and sampled in the vicinity of active hydrothermal vents recently discovered at a site named Broken Spur, 29°10.15'N 43°10.28'W, on the Mid-Atlantic Ridge. The northern plume (29°10.13'N 43°10.61'W) most closely associated with Broken Spur consists of a weak plume (heat flux c. 5 MW), whereas plumes detected to the south (29°09.11'N 43°10.54'W) are much stronger (heat flux c. 57 MW). The plumes are characterized by dissolved 222Rn, Fe and Mn anomalies of up to 20 dpm/100 kg, 32 and 14 nmol/l, respectively, and enhanced concentrations of Fe, Mn, Cu, Zn, Cd, Co and Pb in the particulate phase. Comparison of Fe:Mn ratios in the plume (3.7) to Fe:Mn in vent fluids collected at Broken Spur (7.9) suggests that c. 530f hydrothermal Fe is removed during plume evolution.
