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 Ocean, just north of the Antarctic Polar Front (APF). Recent investigations have shown enhanced primary productivity in its immediate environment due to an island effect. An extensive cruise, covering ≈105 km2 around 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. Overall, the chlorophyll-a (chl-a) values as well as primary productivity were substantially lower on this occasion than those observed previously. The distribution of terrigenous urea and ammonia clearly demarcated the geographical limits of the immediate island effect, which did not extend further than 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 of chl-a. No region of enhanced primary productivity was observed between the islands, a conspicuous feature observed during previous cruises to the area.