Picture: Waves from the Tasman Sea crash on the coastline. Credit: Bernard Spragg Flick4 CC 1.0

Marine heatwaves have recently had dramatic impacts on the ecosystems, fisheries and aquaculture off Tasmania’s east coast.

In this study, CLEX researchers and colleagues investigated the large-scale drivers that led to the development of marine heatwaves off southeast Australia observed from 1994-2016, including the extreme 2015/16 event.

The findings showed that about half of the historical occurrences of marine heatwaves in this region were primarily due to the intensification of the East Australian Current Extension, bringing warmer water with it. But what might have caused these intensifications?

The researchers found that huge, slow moving waves coming from the South Pacific generated by the rotation of the Earth, known as Rossby waves, played an important role. These waves can’t be seen by the naked eye but can be detected with satellites, which see an increase in wave heights over a large region.

Importantly, 2-3 years before the Rossby waves caused the East Australian Current Extension to intensify, their impact could already be seen in changes in sea surface heights around New Zealand. The slow-moving speed of Rossby waves opens the door to the possibility that marine heatwaves that impact southeast Australia may be forecast years in advance, with important implications for fisheries and the environment in this region. 

  • Paper: Li Z, NJ Holbrook, X Zhang, ECJ Oliver and EA Cougnon, 2020: Remote forcing of Tasman Sea marine heatwaves. Journal of Climate, 33, 5337-5354, doi:10.1175/JCLI-D-19-0641.1.