Drivers, Dynamics, and Persistence of the 2017/2018 Tasman Sea Marine Heatwave

During the austral summer of 2017/2018, the Tasman Sea experienced an intense marine heatwave over an extensive area. It persisted for approximately 3 months and caused substantial ecological impacts. The marine heatwave was understood to have been driven primarily by increased net downward heat flux associated with a high pressure system. However, it has been unclear why the marine heatwave persisted. Using an ultra-high-resolution (similar to 1 km) regional ocean model simulation, the drivers, dynamics, and persistence of the 2017/2018 marine heatwave are explored in detail. It is found that a burst of warm water advection helped to initiate the event, but a shallower than usual mixed layer, coupled with near continuous net downward air-sea heat flux, caused the marine heatwave to persist. Submesoscale dynamics were found to be relatively unimportant to the marine heatwave's persistence.