物理海洋学名词-A 4

Glossary of Physical Oceanography and Related Disciplines

Steven K. Baum Department of Oceanography Texas A&M University

May 26, 2004

 

abyssal plain Flat areas of the ocean basin floor which slope less than 1 part in 1000. These were formed by turbidity currents which covered the preexisting topography. Most abyssal plains are located between the base of the continental rise and the abyssal hills. The remainder are trench abyssal plains that lie in the bottom of deep-sea trenches. This latter type traps all sediment from turbidity currents and prevents abyssal plains from forming further seaward, e.g. much of the Pacific Ocean floor. See Fairbridge [1966].
The official IHO definition for this undersea feature name is “an extensive, flat, gently sloping or nearly level region at abyssal depths.”

abyssal zone This originally meant (before the mid-1800s) the entire depth area beyond the reach of fisherman, but later investigations led to its use being restricted to the deepest regions with a uniform fauna and low temperatures. Thus it was distinguished from the overlying bathyal or archibenthal zone with more varied fauna and higher temperatures. Eventually an underlying hadal zone was defined for areas in trenches and deeps below 6000-7000 m depth. The upper boundary of the abyssal zone ranges between 1000-3000 m, with the position of the 4℃ isotherm generally considered the demarcation line. It is the world’s largest ecological unit, with depths exceeding 2000 m comprising over three-quarters of the world ocean. See Fairbridge [1966].

abyssopelagic zone One of five vertical ecological zones into which the deep sea is sometimes divided. There is a pronounced drop in the number of species and the quantity of animals as one passes into this zone. It is separated from the overlying bathypelagic zone by the 4℃ isotherm and from the underlying hadopelagic zone at about 6000 meters. The distinction between pelagic and benthic species can be difficult to ascertain in this zone. See Bruun [1957].

a-c meter An instrument used to perform in-situ measurements of the amount of chlorophyll in water. It does this by pulling water into two tubes, one measuring light absorption and the other attenuation. A beam of light with a wavelength rotating among three values is projected into each tube. The attenuation tube determines light absorption and scattering by measuring how much of the original light beam remains after it passes through the water inside the blackened tube. The absorption tube determines only how much light is absorbed by particles by measuring how much light is left of the original beam including that which has bounded off particles. This tube is lined with a quartz mirror which, in contrast to the absorbing black surface in the attenuation tube, reflects scattered light toward the detector. Chlorophyll causes a large change in the attenuation of light with a wavelength of about 676 nanometers, so a measurement of attenuation at the appropriate wavelength is a proxy measurement of chlorophyll concentration to first order. A fluorometer can also be used to measure chlorophyll.

ACC 1. Abbreviation for the Antarctic Circumpolar Current. 2. Abbreviation for the Alaskan Coastal Current.

ACCE Abbreviation for Atlantic Climate Change Experiment, a joint program between WOCE and NOAA’s ACCP designed to increase understanding of the meridional overturning circulation (MOC) of the Atlantic Ocean and the overlying atmosphere at interannual and longer time scales. The goals of ACCE were:
• to provide a quantitative 4–D observational description of the pathways and material property fluxes of the MOC within the North Atlantic Ocean that vary on time scales from interannual to at least decadal;
• to improve understanding and modeling of the relationships between the rates and natural variability of the MOC, internal ocean properties, SST, and the variability of the overlying atmosphere; and

• to identify and initiate measurements to be continued beyond the ACCE observational period to monitor the variability of important elements of the MOC and its relation to global climate variability.

See WOCE [1995].
[http://www.aoml.noaa.gov/phod/acce/]
[http://www-ocean.tamu.edu/WOCE97/Future/acce.html]

 

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