1. University of Washington, School of Oceanography, Seattle, Washington 98195, USA
2. Duke University, Division of Earth & Ocean Sciences, Durham, North Carolina 27708-0230, USA
3. Scripps Institution of Oceanography, La Jolla, California 92093–0225, USA
4. Institute For Mineralogy and Petrology, ETH-Zentrum, CH-8092, Zurich, Switzerland
5. Joint Institute for the Study of the Atmosphere & Ocean, University of Washington and NOAA Pacific Marine Environmental Laboratory, Seattle, Washington 98115, USA

Correspondence to: Deborah S. Kelley¹ Correspondence and requests for materials should be addressed to D.S.K. (e-mail: Email: kelley@ocean.washington.edu).

Abstract

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.

1. University of Washington, School of Oceanography, Seattle, Washington 98195, USA
2. Duke University, Division of Earth & Ocean Sciences, Durham, North Carolina 27708-0230, USA
3. Scripps Institution of Oceanography, La Jolla, California 92093–0225, USA
4. Institute For Mineralogy and Petrology, ETH-Zentrum, CH-8092, Zurich, Switzerland
5. Joint Institute for the Study of the Atmosphere & Ocean, University of Washington and NOAA Pacific Marine Environmental Laboratory, Seattle, Washington 98115, USA

Correspondence to: Deborah S. Kelley¹ Correspondence and requests for materials should be addressed to D.S.K. (e-mail: Email: kelley@ocean.washington.edu).