Observations if ocean extreme events in Southern Australia
Dr Hugo De Oliveira1, Dr. Mark Doubell1
1Sardi, West Beach, Australia
It is well known that both ENSO and the Southern Annular Mode (SAM) modulate the climate variability in Southern Australia’s shelves. On the one hand, the waveguide of the Australian coastline permits tropical information to travel poleward. On the other hand, the meridional shift of the westerlies (southeasterlies) provides a swift change of conditions along the shelf.
Here we show how cold and heat extremes are distributed within the southern shelves in historical and recent observations. In particular, during the summer of 2016, a stronger El-Nino combined with a positive SAM promoted extreme upwelling by lifting the thermocline and enhancing the northward alongshore shelf currents. The enhanced upwelling boosted primary productivity in narrow bands along the coast, with extremes evident in various variables and observational platforms.
Contrastingly, during early autumn 2021, long-lasting extreme warm conditions were observed in a new remote sensed based Marine Heat Wave (MHW) product. This particular event seems modulated by La-Nina conditions and a weaker SAM, with larger horizontal scales and a reduced coastal upwelling signal.
The MHW product used here is consistent with recently published studies, including a weaker positive trend in the eastern Great Australian Bight over the last two decades. The mean MHW intensity events during the period are above 2°C from climatology, located mainly within the upper gulfs and west of the Bonney Coast. Frequencies of events are typically between one to three per year, with locations such as Coffin and Boston Bay experiencing beyond two events per year. Finally, the duration of events is usually less than two weeks for shallow regions but beyond three weeks in the mid-to-outer shelf.
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Biography:
I’m a research scientist at SARDI, working with operational oceanography, ocean modelling and observations. My main research interests are regional ocean dynamics, ocean modelling and remote sensing. I like to develop tools and products to understand the fundamental dynamics of the ocean and support the environment.
