Elevated chlorophyll alpha concentrations associated with a transient shelfbreak front in a western boundary current at Sydney, south-eastern Australia

A mid-water phytoplankton bloom, measured by a five-fold increase in chloro phyll a concentrations above background levels, occurred in coastal waters off Sydney at depths of 80 100 m directly above the shelfbreak. The physica l feature underpinning the bloom was a transient shelfbreak front that deve loped in response to the concurrent actions of an offshore-directed wind-fo rced bottom boundary-layer flow over the shelf and an onshore-directed bott om boundary-layer flow associated with a meso-scale oceanic eddy over the u pper slope. Never previously have these transient fronts been shown to resu lt in phytoplankton blooms on this shelf. The observations are significant because processes leading to nutrient enrichment and enhanced pelagic prima ry production over continental shelves on western boundaries are in many ca ses not well understood.