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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.

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Shelf waters of southern Australia support the world's only northern boundary current ecosystem. Although there are some indications of intense nitrate enrichment in the eastern Great Australian Bight (GAB) arising from upwelling of the Flinders Current, the biological consequences of these processes are poorly understood. We show that productivity in the eastern GAB is low during winter, but that coastal upwelling at several locations during the austral summer-autumn results in localized increases in surface chlorophyll a concentrations and downstream enhancement of zooplankton biomass. Sardine (Sardinops sagax) and anchovy (Engraulis australis) eggs and larvae are abundant and widely distributed in shelf waters of the eastern and central GAB during summer-autumn, with high densities of sardine eggs and larvae occurring in areas with high zooplankton biomass. Egg densities and distributions support previous evidence suggesting that the spawning biomass of sardine in the waters off South Australia is an order of magnitude higher than elsewhere in southern Australia. Sardine comprised >50% of the identified prey species of juvenile southern bluefin tuna (SBT, Thunnus maccoyii) collected during this study. Other studies have shown that the lipid content of sardine from the GAB is relatively high during summer and autumn. We suggest that juvenile SBT migrate into the eastern and central GAB during each summer-autumn to access the high densities of lipid-rich sardines that are available in the region during the upwelling period. Levels of primary, secondary and fish production in the eastern GAB during summer-autumn are higher than those recorded in other parts of Australia, and within the lower portion of ranges observed during upwelling events in the productive eastern boundary current systems off California, Peru and southern Africa.

Abstract. We employ a three-dimensional hydrodynamic model (COHERENS) in a fully prognostic mode to study the circulation and water mass properties of the Persian Gulf – a large inverse estuary. Our findings, which are in good agreement with observational evidence, suggest that the Persian Gulf experiences a distinct seasonal cycle in which a gulf-wide cyclonic overturning circulation establishes in spring and summer, but this disintegrates into mesoscale eddies in autumn and winter. Establishment of the gulf-wide circulation coincides with establishment of thermal stratification and strengthening of the baroclinic exchange circulation through the Strait of Hormuz. Winter cooling of extreme saline (>45) water in shallow regions along the coast of United Arab Emirates is a major driver of this baroclinic circulation.