Hydrothermal Environments, Marine
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HYDROTHERMAL ENVIRONMENTS, MARINE
Cross-references Cold Seeps Deep Biosphere of the Ocean Deep Sea Extreme Environments Hydrothermal Environments, Marine Iron Sulfide Formation Origin of Life
HYDROTHERMAL ENVIRONMENTS, MARINE Gilberto E. Flores, Anna-Louise Reysenbach Portland State University, Portland, OR, USA
Definition Marine hydrothermal environments are one of the most extreme environments on Earth, yet they support highly productive biological communities over a wide range of physical and chemical environments. The following review is a general discussion of the types of microorganisms found in these different environments preceded by brief descriptions on hydrothermal fluid generation, mineral deposit formation, and microbial metabolism. Introduction The discovery of deep-sea hydrothermal vents and the lush biological communities associated with them in the late 1970s ushered in a new era for marine biologists. Prior to this discovery, life in the deep-sea was thought to be dependent on the settling of detrital material from the productive, overlying surface waters. While this is true for much of the ocean basins, the level of production observed at these newly discovered vent sites was too great to be supported by these mechanisms alone. It soon became evident that life in these environments was supported by chemosynthetic primary production in which microorganisms harnessed the abundant geochemical energy available in the hydrothermal fluids. This challenged one of the basic ecological premises that all ecosystems on Earth were dependent on light energy and driven by photosynthetic primary production. Since those initial revelations, research efforts have focused on assessing the microbial diversity and attempting to understand the intimate associations between microbial productivity, geology, and geochemistry in marine hydrothermal environments. This article is a general discussion of the trends that are beginning to emerge from these efforts. Included in the discussion are overviews of the geologic setting of marine hydrothermal systems, the generation of hydrothermal fluids from different geologic settings, and the types of structures formed. For additional in-depth reviews, the Geophysical Monographs published by the American Geophysical Union (AGU) are valuable resources (Humphris et al.,
1995; German et al., 2004; Wilcock et al., 2004; Christie et al., 2006).
Geological setting Most seafloor hydrothermal vent systems are associated with extensional tectonic activity and heated by magmatic heat as it is convected into the crust (Seyfried and Mottl, 1995). The most well-studied areas of hydrothermal circulation are along divergent plate boundaries where basaltic seafloor is made and mid-ocean ridges (MOR) arise (Figure 1). Hydrothermal circulation along MORs results from the active heating of seawater that percolates through newly formed basaltic crust. Hydrothermal venting is also commonly found along convergent plate margins where an oceanic plate is subducted beneath a continental plate formin
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