Fossil evidence for serpentinization fluids fueling chemosynthetic assemblages
Résumé
Among the deep-sea hydrothermal vent sites discovered in the
past 30 years, Lost City on the Mid-Atlantic Ridge (MAR) is
remarkable both for its alkaline fluids derived from mantle rock
serpentinization and the spectacular seafloor carbonate chimneys
precipitated from these fluids. Despite high concentrations of
reduced chemicals in the fluids, this unique example of a serpentinite-
hosted hydrothermal system currently lacks chemosynthetic
assemblages dominated by large animals typical of high-temperature
vent sites. Here we report abundant specimens of chemosymbiotic
mussels, associated with gastropods and chemosymbiotic
clams, in approximately 100 kyr old Lost City-like carbonates from
the MAR close to the Rainbow site (36 °N). Our finding shows that
serpentinization-related fluids, unaffected by high-temperature
hydrothermal circulation, can occur on-axis and are able to sustain
high-biomass communities. The widespread occurrence of seafloor
ultramafic rocks linked to likely long-range dispersion of vent
species therefore offers considerably more ecospace for chemosynthetic
fauna in the oceans than previously supposed
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