Thirty years after the first discovery of high-temperature submarine venting, the vast majority of the global mid-ocean ridge remains unexplored for hydrothermal activity. Of particular interest are the world's ultraslow spreading ridges that were the last to be demonstrated to host high-temperature venting but may host systems particularly relevant to prebiotic chemistry and the origins of life. Here we report evidence for previously unknown, diverse, and very deep hydrothermal vents along the approximately 110 km long, ultraslow spreading Mid-Cayman Rise (MCR). Our data indicate that the MCR hosts at least three discrete hydrothermal sites, each representing a different type of water-rock interaction, including both mafic and ultramafic systems and, at approximately 5,000 m, the deepest known hydrothermal vent. Although submarine hydrothermal circulation, in which seawater percolates through and reacts with host lithologies, occurs on all mid-ocean ridges, the diversity of vent types identified here and their relative geographic isolation make the MCR unique in the oceans. These new sites offer prospects for an expanded range of vent-fluid compositions, varieties of abiotic organic chemical synthesis and extremophile microorganisms, and unparalleled faunal biodiversity--all in close proximity.
Within a largely steady‐state low‐flux passive margin, a seafloor seep at the Blake Ridge Diapir transiently releases methane gas and sulfide‐laden fluids. Until now, fluid flux estimates on the diapir have been too small to reconcile with seafloor gas emission and the survival of a chemosynthetic community at the seep. Analysis of heat flow and high‐resolution seismic data collected across the diapir confirms fluid flux through a sub‐vertical chimney with apparent fluid velocities between 20 to 400 m ky −1 , ∼100 times larger than previous estimates derived from pore water geochemical data. Away from the chimneys, observations indicate that conductive thermal processes and low fluid fluxes dominate in the hydrate reservoir and that dissolution of the salt diapir does not control the thickness of the hydrate stability zone. The results suggest that, despite limited fluid flux in the larger area, focused flux can be significant enough to sustain a seafloor chemosynthetic community at the diapir.
A decade of Ridge 2000 and related research has yielded new and refined understanding of events and processes that occur on mid-ocean ridge and backarc spreading centers, as reported in this special issue of Oceanography. Exciting exploration has also continued, with the past decade witnessing discovery of vent ecosystems in the Arctic (Pedersen et al., 2010), a new vent biogeographic province in the Southern Ocean (Rogers
The densities of chemoautotrophic and methanotrophic symbiont morphotypes were determined in life- history stages (post-larvae, juveniles, adults) of two species of mussels (Bathymodiolus azoricus and B. heckerae) from deep-sea chemosynthetic environments (the Lucky Strike hydrothermal vent and the Blake Ridge cold seep) in the Atlantic Ocean. Both symbiont morphotypes were observed in all specimens and in the same relative proportions, regardless of life-history stage. The relative abundance of symbiont morphotypes, determined by transmission electron microscopy, was different in the two species: chemoautotrophs were dominant (13:1–18:1) in B. azoricus from the vent site; methanotrophs were dominant (2:1–3:1) in B. heckerae from the seep site. The ratio of CH4:H2S is proposed as a determinant of the relative abundance of symbiont types: where CH4:H2S is less than 1, as at the Lucky Strike site, chemoautotrophic symbionts dominate; where CH4:H2S is greater than 2, as at the seep site, methanotrophs dominate. Organic carbon and nitrogen isotopic compositions of B. azoricus (δ13C = −30‰; δ15N = −9‰) and B. heckerae (δ13C = −56‰; δ15N = −2‰) varied little among life-history stages and provided no record of a larval diet of photosynthetically derived organic material in the post-larval and juvenile stages.
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