Cross-shelf transport in the East Australia Current separation Zone (#114)
The East Australian Current (EAC) flows along the narrow continental shelf of SE Australia, forming an intense eddy field downstream of its separation point. The mesoscale circulation has a significant impact on driving cross shelf fluxes and shelf - open ocean exchange. Long term records of sea surface height (AVISO altimetry) reveal a persistent eddy dipole feature immediately downstream of the EAC separation zone. Both ecological data and particle trajectory modelling shows the adjacent coastline inshore of this dipole experiences a peak in the settlement rates of larvae, associated with onshore transport between the eddy dipole. Here we investigate the biophysical characteristics of this persistent dipole feature using a wide range of in-situ observations, firstly in a case study captured during a research cruise and then in a broader sense, looking at the prevalence of the dipole and its impact on the shelf circulation over time. The feature is associated with strong cross-shelf velocities that drive the exchange of biologically rich water between the shelf and the deep ocean. To explore the impact of this feature, it is then placed into context by quantifying the cross-shelf transports associated with this and other dominant modes of variability in the EAC’s separation from the shelf. These estimates are made using both satellite observations and 20 years of hind-cast model output. Results suggest that the EAC Eddy dipole is a dominant mechanism driving cross shelf exchange and productivity in what is arguably an oligotrophic region.