earth science ch. 9
Composition of Seawater
Terms
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- oceanic (mid-ocean) ridge
- a continuous elevated zone on the floor of all the major ocean basins and varying in width from 500 to 5000 kilometers (300 to 3000 miles). the rifts at the crests of these ridges represent divergent plate boundaries
- thermocline
- a layer of water in which there is a rapid change in temperature in the verticle dimension
- continental shelf
- the gently sloping submerged portion of the continental margin extending from the shoreline to the continental slope
- seamount
- an isolated volcanic peak that rises at least 1000 meters (3000 ft) above the deep-ocean floor
- sonar
- an instrument that uses acoustic signals (sound energy) to measure water depths. sonar is an acronym for sound navigation and ranging.
- terrigenous sediment
- seafloor sediment derived from weathering and erosion on land
- guyot [ table mount ]
- a submerged flat-topped seamount
- hydrogenous sediment
- seafloor sediments consisting of minerals that crystallize from seawater. an important example is manganese nodules
- salinity
- the proportion of dissolved salts to pure water, usually expressed in parts per thousand ( 0/00 )
- biogenous sediment
- seafloor sediments consisting of material of marine-organic orgin
- submarine canyon
- a seaward extension of a valley that was cut on the continental shelf during a time when sea level was lower, or a canyon carved into the outer continental shelf, slope, and rise by turbidity currents
- deep ocean trench
- a narrow, elongated depression on the floor of the ocean
- continental rise
- the gently sloping surface at the base of the continental slope
- deep sea fan
- a cone-shaped deposit at the base of the continental slope. the sediment is transported to the fan by turbidity currents that follow submarine canyons
- continental margin
- that portion of the seafloor adjacent to the continents. it may include the continental shelf, continental slope, and continental rise
- continental volcanic arc
- mountains formed in part by igneous activity associated with the subduction of oceanic lithosphere beneath a continent. ex the Andes and the Cascades
- abyssal plain
- very level area of the deep-ocean floor, usually lying at the foot of the continental rise
- echo sounder
- an instrument used to determine the depth of water by measuring the time interval between emission of a sound signal and the return of its echo from the bottom
- rift valley
- a region of earth's crust along which divergence is taking place
- bathymetry
- the measurement of ocean depths and the charting of the topography of the ocean floor
- continental slope
- the steep gradient that leads to the deep-ocean floor and marks the seaward edge of the continental shelf
- passive continental margin
- margin that consists of a continental shelf, continental slope, and continental rise. they are not associated with plate boundaries and therefore experience little volcanism and few earthquakes
- halocline
- a layer of water in which there is a high rate of change in salinity in the vertical dimension
- volcanic island arc
- a chain of volcanic islands generally located a few hundred kilometers from a trench where there is active subduction of one oceanic plate beneath another
- outgassing
- the escape of gases that had been dissolved in magma
- oceanography
- the scientific study of the oceans and oceanic phenomena
- turbidity current
- a downslope movement of dense, sediment-laden water created when sand and mud on the continental shelf and slope are dislodged and thrown into suspension
- active continental margin
- usually narrow and consisting of highly deformed sediments. they occur where oceanic lithosphere is being subducted beneath the margin of a continent