Pelagic Open ocean environment. A marine sedi- ment with that fraction derived from the conti- nents indicating deposition from a dilute suspension distributed throughout deep-sea water. Phyllosilicate Layered or sheet silicate mineral, formed by sharing three of the four oxygens in neighboring silicon tetrahedra. Plankton Aquatic organisms that drift, or swim weakly. Can be either plants (phytoplankton) or animals (zooplankton). Redox Abbreviation for reduction}oxidation, usu- ally expressed as a potential. Seamount Underwater mountain, 1000 m or higher elevation from seaSoor base. Morphology may be peaked or Sat-topped, with the latter called guyot. Suboxic Condition lacking free oxygen, but not extremely reducing. Zeolite Any of the minerals of the zeolite group. Aluminosilicate minerals with an open framework structure that allows for easily reversible hy- dration, gas adsorption, and either cation or ani- on exchange. See also Aeolian Inputs. Clay Mineralogy. Hydrothermal Vent Deposits. Manganese Nodules. Mineral Ex- traction, Authigenic Minerals. Platinum Group Ele- ments and their Isotopes in the Ocean. Pore Water Chemistry. Rare Earth Elements and their Iso- topes in the Ocean. River Inputs. Sediment Chro- nologies. Sedimentary Record, Reconstruction of Productivity from the. Tracers of Ocean Productiv- ity. Transition Metals and Heavy Metal Speciation. Uranium+Thorium Decay Series in the Oceans Overview. Further Reading Bentor YK (ed.) (1980) Marine Phosphorites; a Sympo- sium, Oklahoma: SEPM Special Publication no. 29. Burns RG and Burns VM (1981) Authigenic oxides. In: The Sea, vol. 7, pp. 875}914. New York: Wiley. Chamley H (1989) Clay Sedimentology. Berlin: Springer- Verlag. Cronan DS (1974) Authigenic minerals in deep-sea sedi- ments. In: Goldberg ED (ed.) The Sea, vol. 5, pp. 491}525. New York: Wiley. Cronan DS (1980) Underwater Minerals. London: Aca- demic Press. Cronan DS (ed.) (2000) Handbook of Marine Mineral Deposits. Boca Raton, FL: CRC Press. Glasby GP (ed.) (1977) Marine Manganese Deposits. Else- vier Oceanography Series. Amsterdam: Elsevier. Glenn CR, Pre H vot-Lucas L and Lucas J (eds.) (2000) Marine Authigenesis: from Global to Microbial. Oklahoma: SEPM Special publication no. 66. Halbach P, Friedrich G and von Stackelberg U (eds.) (1988) The Manganese Nodule Belt of the PaciTc Ocean: Geological Environment, Nodule Formation, and Mining Aspects. Stuttgart: F. Enke Verlag. Kastner M (1981) Authigenic silicates in deep-sea sedi- ments: formation and diagenesis. In: Emiliani C (ed.) The Sea, vol. 7, 915}980. New York: Wiley. Manheim FT (1986) Marine cobalt resources. Science 232, 600}608. Margolis SV and Burns RG (1976) PaciRc deep-sea man- ganese nodules: their distribution, composition, and origin. Annual Review of Earth and Planetary Science 4: 229}263. AUTONOMOUS UNDERWATER VEHICLES (AUVs) James Bellingham, MIT Sea Grant, Cambridge, MA, USA Copyright ^ 2001 Academic Press doi:10.1006/rwos.2001.0303 An autonomous underwater vehicle (AUV) is an uncrewed, untethered, underwater vehicle capable of self-propulsion. Such vehicles are mobile instru- mentation platforms that have actuators, sensors, and on-board intelligence to successfully complete survey and sampling type tasks with little or no human supervision. A large number of AUVs have been developed, ranging in dry weights from less than 50 kg to nearly 9000 kg, with the majority of vehicles at the small end of the scale. In the last several years, acceptance of AUVs for oceano- graphic, commercial, and military missions has risen dramatically, leading to a sharp rise in AUV opera- tions. By far the most common AUV conRguration is as a torpedo-like vehicle, consisting of a streamlined body with propeller and control surfaces at the stern (Figure 1). Operational speeds for such vehicles range from 0.5 to 5 m s 1 , with most vehicles oper- ating at a cruising speed of about 1.5 m s 1 . In order to remain controllable, torpedo-like AUVs must move forward at some minimum speed in order to maintain Sow over control surfaces, and therefore are not capable of station keeping. When a higher 212 AUTONOMOUS UNDERWATER VEHICLES (AUVs)