Lost City

Lost City, located 20 km west of the Mid-Atlantic Ridge, is characterized by extreme conditions never before seen in the marine environment: venting of pH 9-11, >90°C, metal-poor fluids from carbonate edifices that tower 60-m above the seafloor. Investigation of this remarkable system has forever changed our views about where and how life can thrive and survive on and in the seafloor and provided new models for the evolution of life on this earth and possibly elsewhere [Kelley et al., 2005]. This system is the longest-lived of any known venting environment in the worlds’ oceans with activity ongoing for at least 120,000 years. Investigations of this site were funded by the National Science Foundation and by the NOAA Ocean Exploration program.

Within the Atlantis Massif, a >14,000 foot tall mountain on which Lost City rests, fluid rock reactions in the ultramafic rocks result in alkaline fluids with high concentrations of abiogenically produced hydrogen, methane, and other low molecular weight hydrocarbons. In concert, these dissolved gases support novel microbial communities. The oxygen-free, interior zones of the chimneys harbor biofilms of a single type of archaea called Lost City Methanoscarcinales that utilizes methane in its metabolism. Bacteria related to CH4- and S-oxidizers, are mostly found in the oxygenated, outer walls of chimneys where fluid chemistry is substantially different than the chimney interiors [Brazelton et al., 2006].

The highly-sculpted, high-surface area of the Lost City structures provides ample space for faunal habitats, and many recovered invertebrates were located within the porous channels and crevices of the carbonate. Surprisingly, while total biomass is low within the field, the field supports a species diversity that appears to be as high as any other known black smoker system on the Mid-Atlantic Ridge spreading center.

The range and complexity of environments hosting peridotites and other ultramafic rocks within the worlds’ oceans is vast and it is unlikely that Lost City is unique. Perhaps the most far-reaching impact of the discovery Lost City-type is the realization that life itself may have originated within these dynamic environments in which geological, chemical, and biological processes are intimately linked.