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

Abstract

A mid-water phytoplankton bloom, measured by a five-fold increase in chlorophyll a concentrations above background levels, occurred in coastal waters off Sydney at depths of 80–100 m directly above the shelfbreak. The physical feature underpinning the bloom was a transient shelfbreak front that developed in response to the concurrent actions of an offshore-directed wind-forced bottom boundary-layer flow over the shelf and an onshore-directed bottom boundary-layer flow associated with a meso-scale oceanic eddy over the upper slope. Never previously have these transient fronts been shown to result in phytoplankton blooms on this shelf. The observations are significant because processes leading to nutrient enrichment and enhanced pelagic primary production over continental shelves on western boundaries are in many cases not well understood.