Fossil evidence for serpentinization fluids fueling chemosynthetic assemblages

Abstract

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.Bathymodiolus | Ghost City | ultramafic-hosted | mid-ocean ridge | ecogeochemistry H igh-temperature hydrothermal vents occur at very geographically restricted sites in the deep-sea, localized on spreading ridges and arc-related volcanoes. Typically, such vent fluids are metal-and H 2 S-rich and precipitate metallic sulfide chimneys on the seafloor (1, 2). These vents usually support high-biomass invertebrate communities, dominated by a small number of endemic species forming symbioses with diverse

A serpentinite-hosted ecosystem in the Southern Mariana Forearc

“…Our DSV Shinkai 6500 diving and earlier dredging (19,20) indicates that the deep geology of the southern Mariana forearc is dominated by peridotite and is heavily faulted, suggesting that more SSF-type seeps exist along the southern Mariana forearc, and perhaps, along the other nonaccretionary convergent margins like the Tonga forearc where extensive peridotite exposures in the deep forearc also are known (33). Our discovery supports the prediction that serpentinite-hosted vents may be widespread on the ocean floor (5,30,31). The discovery further indicates that these serpentinite-hosted low-temperature systems can sustain high-biomass communities.…”

“…Although vesicomyid clams are among the dominant invertebrates of chemosynthesis-based communities found at hydrothermal vents, cold seeps, and whale carcasses, there have been no live examples from a serpentinitehosted hydrothermal system including serpentinite mud volcanoes, except for the high-temperature serpentinite and gabbro-hosted system at Logatchev (26,27) and the Vema Fracture Zone (although the hydrothermal activity in this location has yet to be documented) (25,29). Fossil vesicomyid clams have however recently been reported from two sites near the high-temperature serpentinite and gabbro-hosted system at Rainbow (30,31). It should be noted, however, that one of these sites, the Ghost City field, was not a high-temperature system when it was active approximately 110 kyr ago (31).…”

“…Fossil vesicomyid clams have however recently been reported from two sites near the high-temperature serpentinite and gabbro-hosted system at Rainbow (30,31). It should be noted, however, that one of these sites, the Ghost City field, was not a high-temperature system when it was active approximately 110 kyr ago (31). The SSF vesicomyid clam community is therefore an important live example of a low-temperature serpentinite-hosted hydrothermal system from either convergent or divergent margins, extending our knowledge about the biogeography of these clams.…”

A hydrothermal seep on the Costa Rica margin: middle ground in a continuum of reducing ecosystems

“…R. Soc. B (2012) [67], a subduction seep off Hatsushima Island, Sagami Bay exhibiting elevated temperatures [4], other fore-arc seamounts where extensional spreading induces hydrothermal circulation, and thermogenic methane is released [68], and possibly at serpentinite-hosted hydrothermal systems such as Lost City and Ghost City on the Mid-Atlantic Ridge [69].…”

Fluid mixing and the deep biosphere of a fossil Lost City-type hydrothermal system at the Iberia Margin

“…C (δ 13 C TOC = −19.4‰). We detected a combination of bacterial diether lipid biomarkers, archaeol, and archaeal tetraethers analogous to those found in carbonate chimneys at the active Lost City hydrothermal field.…”