abyssal zone
A
abiotic (opposite to biotic) lifeless, a term used for characteristics and elements
of the environment with a certain influence on survival or reproduction of
organisms that are not alive themselves. Examples are temperature, light,
nutrients, etc., also denoted as abiotic factors or substances.
absolute age (geol.) age in years. Age measurement is usually based on radioactive dating, a method in which the known rate of decay of a radioactive "parent" element into a stable or radioactive "daughter" element is applied to the
measured, present-day ratio of these two elements. There are several useful
combinations of elements, such as uranium-lead, potassium-argon (K-Ar),
rubidium-strontium, and 14C_ 12 C. The 14C method can be used on carbonate or organic material for direct dating of young sediments, while the K -Ar
method is used on glauconite, a mineral that is formed on the sea floor.
--7radioisotopes.
absorption (1) (chern.) --7sorption; (2) (radiation) --7optics.
abundance (syn. density, bioI.) number of organisms per unit of habitat space.
Indices of relative abundance may be useful, for example number of birds
seen per hour or percentages of samples occupied by a species. --7concentration.
abyssal hill low relief feature of the ocean floor, ranging up to several hundred
meters in height and several kilometers in diameter. About 85 % of the
Pacific Ocean floor and 50 % of the Atlantic Ocean floor are covered by
abyssal hills. --7sea-f1oor topography, --7seamount and --7tablemount.
abyssal plain area of the ocean-basin floor that is flat, with a slope of less than
1:1000. Abyssal plains are among the flattest portions of the earth's surface.
They occur adjacent to the outer margins of the continental slope, between 3000
and 6000 m deep. The horizontal extent of an abyssal plain ranges from less
than 200 km to more than 2000 km. Some have a flat surface with a continuous gradient in one direction, whereas others are marked by broad irregularities. They are widespread in the Atlantic and Indian oceans and occur in
marginal seas such as the western Mediterranean, Gulf of Mexico, and the
Caribbean.
abyssal zone zone over the abyssal plain, --7lonation.
A
abiotic (opposite to biotic) lifeless, a term used for characteristics and elements
of the environment with a certain influence on survival or reproduction of
organisms that are not alive themselves. Examples are temperature, light,
nutrients, etc., also denoted as abiotic factors or substances.
absolute age (geol.) age in years. Age measurement is usually based on radioactive dating, a method in which the known rate of decay of a radioactive "parent" element into a stable or radioactive "daughter" element is applied to the
measured, present-day ratio of these two elements. There are several useful
combinations of elements, such as uranium-lead, potassium-argon (K-Ar),
rubidium-strontium, and 14C_ 12 C. The 14C method can be used on carbonate or organic material for direct dating of young sediments, while the K -Ar
method is used on glauconite, a mineral that is formed on the sea floor.
--7radioisotopes.
absorption (1) (chern.) --7sorption; (2) (radiation) --7optics.
abundance (syn. density, bioI.) number of organisms per unit of habitat space.
Indices of relative abundance may be useful, for example number of birds
seen per hour or percentages of samples occupied by a species. --7concentration.
abyssal hill low relief feature of the ocean floor, ranging up to several hundred
meters in height and several kilometers in diameter. About 85 % of the
Pacific Ocean floor and 50 % of the Atlantic Ocean floor are covered by
abyssal hills. --7sea-f1oor topography, --7seamount and --7tablemount.
abyssal plain area of the ocean-basin floor that is flat, with a slope of less than
1:1000. Abyssal plains are among the flattest portions of the earth's surface.
They occur adjacent to the outer margins of the continental slope, between 3000
and 6000 m deep. The horizontal extent of an abyssal plain ranges from less
than 200 km to more than 2000 km. Some have a flat surface with a continuous gradient in one direction, whereas others are marked by broad irregularities. They are widespread in the Atlantic and Indian oceans and occur in
marginal seas such as the western Mediterranean, Gulf of Mexico, and the
Caribbean.
abyssal zone zone over the abyssal plain, --7lonation.