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Abstract:
The East Australian Current (EAC) is the western boundary current closing the South Pacific Gyre, it flows along the East Coast of Australia from the Coral Sea until its separation point where it veers eastward, or extends southward. It is a barrier between productive shelf waters and two different water masses offshore: oligotrophic waters upstream of the separation point and productive waters downstream. Besides, the meandering and instabilities of the current locally generate fine-scale structures, known to strongly influence primary productivity. These processes all influence the chlorophyll-a distribution at various scales, and are both influenced by large scale EAC patterns. However, the link between fine-scale and large scale variability remains understudied, and is rarely linked to water mass exchanges. Surface velocity data from two high frequency radar systems located around the coherent jet of the EAC (1.5km) and at its usual separation point (6km) enable the identification of typical scenarii of EAC separation dynamics, that we couple with remote sensed surface chlorophyll-a concentration (4km). A clear relationship between the EAC separation and the inshore circulation’s rotational characteristics is observed. Moreover, the presence of the EAC yields to high strain and vorticity structures, usually associated to strong values of chlorophyll-a anomalies. Overall, chlorophyll-a variability due to fine-scale dynamical properties of the surface flow can reach the same order of magnitude as the variability due to the EAC barrier role. Ultimately, we aim to characterize the chlorophyll-a response to each EAC separation scenario at both large and fine scale.
