Hydrodynamic Drivers of the 2013 Marine Heatwave on the North West Shelf of Australia

The 2012/2013 Ningaloo Niño induced a strong marine heatwave (MHW) event on Australia's North West Shelf (NWS) during the austral summer, starting in December 2012 and peaking in January and February 2013. A high-resolution regional numerical model based on the Regional Ocean Modeling System (ROMS) was implemented to simulate the variability of the upper ocean temperature and ocean circulation and understand the mechanisms that drive the evolution of the MHW. An upper ocean heat budget was used to quantify the roles of air-sea heat flux and ocean circulation in the development of extreme temperature anomalies over the continental shelf. Results indicate that during December 2012 an increase of net air-sea heat flux combined with positive horizontal advective heat flux anomaly led to development of the MHW. During the peak in January-February 2013 high-temperature anomalies were maintained by a combination of a decrease in negative heat advection and vertical mixing cooling and a decrease in net air-sea flux warming. The delayed onset of the 2012–2013 Australian monsoon resulted in alongshore wind anomalies on the NWS which in turn caused the advection and mixing anomalies.