Deep Biosphere of the Oceanic Deep Sea
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Halobacteria – Halophiles Saline Lakes Salinity History of the Earth’s Ocean Terrestrial Deep Biosphere
DEEP BIOSPHERE OF SEDIMENTS See entries “Terrestrial Deep Biosphere,” “Deep Biosphere of Salt Deposits,” “Deep Biosphere of the Oceanic Deep Sea,” and “Basalt (Glass, Endoliths).”
DEEP BIOSPHERE OF THE OCEANIC DEEP SEA Kristina Rathsack, Nadia-Valérie Quéric, Joachim Reitner University of Göttingen, Göttingen, Germany
Definition and overview Although used in many different ways, the term “biosphere” is principally defined either as zone in which life occurs, thereby overlapping the atmosphere, the hydrosphere, and the lithosphere, or as the entity of living organisms on Planet Earth. Both perceptions commonly focus on the Earth’s near-surface environment, with all domains sharing solar energy used in the process of photosynthesis. The deep-sea realm takes a special position in this context, as deep-sea pelagic and the majority of benthic organisms live in the ocean’s aphotic zone and inhabit the widespread abyssal plains, respectively. For a long time, their main food source has been considered to be based on particulate organic matter (POM) from the ocean’s surface primary production and its sedimentation to abyssal depths (Gage and Tyler, 1991 and references therein, D’Hondt et al., 2002, 2004). With the discovery of “ocean vents” in the late 1970s (Corliss et al., 1979), this general perspective was broadened by the perception of the enormous potential of chemical energy through the reaction of seawater, rock material, and fluids rising from the Earth’s interior. According to this concept of energy for life, the term ‘surface biosphere’ has been opposed to ‘subsurface biosphere’ (also commonly found in literature as ‘deep biosphere’). Following this definition, the deepseafloor with its highly diverse topography from heterotrophic to pure chemotrophic habitats has to be treated as a transition zone between both biospheres. Opposed to the “deep hot biosphere” (Gold, 1992), occurring by definition in oceanic as well as terrestrial subsurface environments, stands the “deep cold biosphere” as defined for permafrost sediments (Vorobyova et al., 1997) and ice cores from the depths of Lake Vostoc (Venter, 2001). Life in the deep sea Comprising approximately 65% of the Earth’s surface, the deep-sea environment is characterized by hyperbaric, aphotic, and low-temperature conditions and highly
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diverse seascapes. Canyons, seamounts, ridges, fractures, and trenches, but also biogeochemical oases such as cold seeps, mud volcanoes, carbonate mounds, brine pools, gas hydrates, hot vent systems, and deep-water coral reefs provide ample niches for a highly diverse pelagic and benthic deep-sea community (Tyler, 2003). It was only during the construction of the transoceanic telegraphic communication network that people realized the ocean’s topographic alterations and astonishing depths. In 1861, the repair of an overgrown cable from 1,800 m water depth in the Mediterranean finally aroused the scientific community which
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