Evidence of a large seasonal coastal upwelling system along the southern shelf of Australia

Abstract

We report observational existence of a large seasonal coastal upwelling system that establishes in austral summer (December–April) along Australian southern shelves. Wind‐driven upwelling events occur simultaneously in three upwelling centres spanning a distance of ∼800 km. During each summer period there are ∼2–3 major upwelling events, each lasting ∼1 week. The simultaneous, rapid response of SST to wind forcing in the upwelling centres, which display vastly different shelf widths, points to the existence of a larger‐scale process that carries cold water onto the shelf prior to the upwelling season. Exploration of a major upwelling event in March 1998 shows the evolution of peak surface chlorophyll‐a concentrations of >4 μg/L lagging the onset of upwelling by ∼1 week. The associated (exponential) growth rate can be estimated at 0.4 d−1. Another week later we found a distinct sub‐surface chlorophyll‐a maximum at a depth of 50 m centred along the upwelling front. Reasons for the formation of this maximum are not fully understood.