物理海洋学名词-A 13

Glossary of Physical Oceanography and Related Disciplines

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

May 26, 2004

 

aguaje A condition observed annually in the coast water off Peru in which the water is discolored red or yellow and there is a significant loss of marine life. It typically occurs from April through June and is probably caused by an increase in water temperatures via the importation of warmer waters by ocean currents. This causes the death of temperature sensitive marine organisms such as dinoflagellates, which may in turn kill other organisms via the release of toxins. The annual nature of this phenomenon makes it distinct from the El Nino phenomenon occurring in the same region. This is also known as salgaso or aqua enferma.


Agulas Basin An ocean basin located off the southern tip of Africa at about 43◦S in the South Atlantic Ocean. It includes the Agulhas Abyssal Plain. See Fairbridge [1966].


Agulhas Current The western boundary current in the Indian Ocean south of 30◦S. The southern Agulhas Current flows southwestward as a narrow jet along a steep continental slope, and is normally pinned to within 10–15 km of its mean position at latitudes 28.5–34◦S. Large meanders – called the Natal pulse – can sometimes occur within this region. These extend an average of 170 km offshore with downstream propagation rates of about 21 cm s−1, with the rates decreasing to 5 cm s−1 as the continental shelf broadens near 34◦S. At this point the current separates from the coast and continues southwestward along the Agulhas Bank, where many meanders, plumes and eddies exist. The maximum transport of the Agulhas occurs in the vicinity of Agulhas Bank, where transport estimates range from 95 to 136 Sv. The core of the current has been defined as where surface velocities exceed 100 cm s−1, with the core averaging about 34 km wide with a mean peak speed of 136 cm s−1 (with a greatest peak speed of 245 cm s−1). 

At around 36◦S the Agulhas leaves the continental shelf and develops oscillations of increasing amplitude, eventually retroflecting back toward the Indian Ocean in the region of 16–20◦E as the Agulhas Return Current. The retroflection loop usually encloses a pool of Indian Ocean surface water south of Africa whose temperature is more than 5◦ warmer than South Atlantic surface water at similar latitudes. The core of the Return Current infrequently passes over the Agulhas Plateau. See Lutjeharms and van Ballegooyen [1988] and Peterson and Stramma [1991].


Agulhas Front (AF) A strong subsurface to intermediate depth front beneath the upper 100–150 m that originates at around 20◦–25◦E below the southern tip of Africa. It extends to between 65◦–90◦E where it merges with the Southern Subtropical Front in the Indian Ocean sector of the ACC. The chief identification criterion is usually the depth range of the 10◦ isotherm, about 300–800 m south of Africa at 16◦–27◦E. This range shrinks to about 400–650 m to the east in the Kerguelan-Amsterdam passage, indicating the gradual weakening of the AF. A thermostad on the warm side of the AF in the 150–300 m layer is another useful identification criterion. This thermostad cools and freshens to east, ranging from 17◦–18◦C/35.5–35.6 at 20◦E to 12◦–14◦C/35.2–35.4 at 70◦E. See Belkin and Gordon [1996].


Agulhas Retroflection See Peterson and Stramma [1991] and Lutjeharms et al. [1992].

 

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