Evidence is growing that hydrothermal venting occurs not only along mid-ocean ridges but also on old regions of the oceanic crust away from spreading centres. Here we report the discovery of an extensive hydrothermal field at 30° N near the eastern intersection of the Mid-Atlantic Ridge and the Atlantis fracture zone. The vent field—named ‘Lost City’—is distinctly different from all other known sea-floor hydrothermal fields in that it is located on 1.5-Myr-old crust, nearly 15 km from the spreading axis, and may be driven by the heat of exothermic serpentinization reactions between sea water and mantle rocks. It is located on a dome-like massif and is dominated by steep-sided carbonate chimneys, rather than the sulphide structures typical of ‘black smoker’ hydrothermal fields. We found that vent fluids are relatively cool (40–75 °C) and alkaline (pH 9.0–9.8), supporting dense microbial communities that include anaerobic thermophiles. Because the geological characteristics of the Atlantis massif are similar to numerous areas of old crust along the Mid-Atlantic, Indian and Arctic ridges, these results indicate that a much larger portion of the oceanic crust may support hydrothermal activity and microbial life than previously thought.
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Shipboard party participants on cruise AT03-60 include N. Bacher, M. Basgall, D. K. Blackman, J. Cann, G. L. Frith-Green, J. S. Gee, H. Hanna, S. D. Hurst, B. E. John, J. A. Karson, D. S. Kelley, S. Lyons, J. Morgan, S. Nooner, P. Rivizzigno, D. K. Ross, G. Sasagawa and T. Schroeder. We thank the pilots, officers and crew of the RV Atlantis-Alvin for their professional service during this cruise. We are also grateful to the operators of ArgoII for their expert navigation of the camera system during the discovery exploration dive to this field. We also thank P. Hickey for piloting of Alvin, his sampling and his observation during the submersible dive. Support for this program was provided by the National Science Foundation.
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Kelley, D., Karson, J., Blackman, D. et al. An off-axis hydrothermal vent field near the Mid-Atlantic Ridge at 30° N. Nature 412, 145–149 (2001). https://doi.org/10.1038/35084000
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