Plankton community structure in the physical environment surrounding the Prince Edward Islands (Southern Ocean) |
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Authors: | P W Froneman I J Ansorge E A Pakhomov J R E Lutjeharms |
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Institution: | (1) Southern Ocean Group, Department of Zoology & Entomology, Rhodes University, Box 94, Grahamstown 6140, South Africa e-mail: zopf@warthog.ru.ac.za Fax: +27-461-24377, ZA;(2) Ocean Climatology Research Group, Department of Oceanography, University of Cape Town, Rondebosch 7701, South Africa, ZA |
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Abstract: | The results are presented of a macroscale physical and biological oceanographic survey conducted during the second Marion
Island Offshore Study in the upstream and downstream regions of the Prince Edward Islands in the austral autumn (April/May)
1997. Upstream of the islands, the Sub-Antarctic Front appeared to combine with the Antarctic Polar Front to form an intensive
frontal feature. Closer to the islands, the fronts appeared to separate. Influenced by the shallow topography of the southwest
Indian ridge, the Sub-Antarctic Front was steered northwards around the islands while the Antarctic polar front appeared to
meander eastwards, where it was again encountered in the southeastern corner of the survey grid. Downstream of the islands,
an intensive cold-core eddy within the Polar Frontal Zone was observed. Its exact genesis is unknown but it is possibly generated
by instabilities within the meandering Antarctic polar front as its surface signature was characteristic of Antarctic surface
water masses found south of the Antarctic polar front. The cold-core eddy appeared to displace the sub-Antarctic front northwards.
South of the eddy, a warm patch of sub-Antarctic surface water was observed; its position appeared to be controlled by the
meandering Antarctic Polar Front which lay on either side of this feature. No distinct microphytoplankton groupings could
be distinguished by numerical analyses, although four distinct zooplankton groupings were identified. These corresponded to
the sub-Antarctic surface waters, Antarctic surface waters and the polar frontal zone waters. The fourth grouping comprised
those stations where the lowest zooplankton abundances during the entire investigation were recorded and, as a consequence,
does not reflect any spatial patterns. These results suggest that the species composition and distribution of plankton in
the vicinity of the islands were consistent with the prevailing oceanographic regime.
Accepted: 15 March 1999 |
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