Mapping deep-water chemosynthetic-based seabed habitats from the southern NE Atlantic: from cold seeps to hot vents

Abstract

Chemosynthetic-­-based ecosystems linked to magmatic/hydrothermal vents (lava volcanoes, hydrothermal vents, and sills-­-induced supercritical hydrothermal fluids) and biogenic/abiogenic methane seeps (mud volcanoes, pockmarks, brine pools, serpentinite diapirs) are living in large range of geological settings, from continental margins, oceanic crust basins, seamounts to mid oceanic ridges shaped by diverse oceanographic dynamics and geological processes. Chemosynthetic-­-based communities require distinct habitats but two main factors are common to maintain their populations: a) the release of deep seated fluids containing biogenic/abiogenic methane or other hydrocarbons, sulphur, iron, carbon dioxide; and b) hard substrate habitats as hard grounds (e.g. ferromanganese crusts), hydrothermal chimneys or methane derived-­-authigenic carbonates (MDACs) chimneys or pavements. Since 2000, extensive research on cold seeps in the southern NE Atlantic Ocean has resulted in the discovery of more than 60 mud volcanoes as well as of several mounds containing MDACs chimneys that are gathered in different fields. Chemosynthetic populations include sulphate reducing bacteria and methanotrophic archea (forming symbioses for AOM, anaerobic oxidation of methane), sulphur-­-oxidizing bacterial mats, tubeworms and extensive beds of clams and deep-­-sea mussels like Bathymodiolus sp. In addition, cold-­-water corals (CWC) living reefs, mounds and ridges, mainly composed of Lophelia pertusa, are extensively identified in association with cold seep build-­-ups as mud volcanoes. In areas of such extensive hydrocarbon seeps, massive authigenic carbonates are the dominant substrate for CWC colonisation and reef formation. Moreover, in the Macaronesia volcanic archipelagos (Canary-­-Azores-­-Madeira-­-Cape Verde), recent submarine eruptions as El Hierro volcano have allowed to identify the growth of new ecosystems associated with emissions of large quantities of iron and carbon dioxide from hydrothermal submarine vents. The seabed mapping of these deep-­-water habitats require a broad variety of geophysical system as multibeam echo-­-sounder (MBES) including bathymetry and backscatter data, parametric sub-­-bottom profilers, high-­-frequency echo-­-sounders and Remote Operated Vehicle (ROV). These techniques allowed us to map these seabed hotspot habitats hosting chemosynthetic communities and associated fauna.

Full text

Mapping deep-water chemosynthetic-based seabed habitats from
the southern NE Atlantic: from cold seeps to hot vents
Luis Somoza
Marine Geology Dv., Geological Survey of Spain (IGME)
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