Biological-physical interactions and pelagic productivity at the Prince Edward Islands, Southern Ocean

The Prince Edward Islands lie in the subantarctic zone of the Southern Ocea n, just north of the Antarctic Polar Front (APF). Recent investigations hav e shown enhanced primary productivity in its immediate environment due to a n island effect. An extensive cruise, covering approximate to 10(5) km(2) a round the island group was carried out to study this supposed island effect in a wider setting. We report here on the biological productivity relative to the physico-chemical environment during the period 7-19 April 1989. Ove rall, the chlorophyll-a (chl-a) values as well as primary productivity were substantially lower on this occasion than those observed previously. The d istribution of terrigenous urea and ammonia clearly demarcated the geograph ical limits of the immediate island effect, which did not extend further th an 80 km off-shore. The hydrography exhibited strong flow past the islands and a distinct wake downstream of the archipelago. Vortices associated with this wake showed some degree of spatial covariance with the distribution o f chi-a. No region of enhanced primary productivity was observed between th e islands, a conspicuous feature observed during previous cruises to the ar ea. (C) 2000 Elsevier Science B.V. All rights reserved.