What is it about?
During summer 2011, a marine heatwave caused warming over hundreds of kilometers off the west coast of Australia. We used an ocean model, validated with mooring observations, to determine the causes of this warming event. We found that the Leeuwin Current was stronger than normal, causing 2/3 of the warming, as it carried warm tropical waters southward along the coast. The other 1/3 of the warming was caused by positive air-sea heat flux into the ocean. The Leeuwin Current intensified due to local and remote wind forcing. Southerly winds, which tend to oppose the Leeuwin Current, were weaker than normal. In the Western Pacific Ocean, anomalous equatorial easterly winds occurred associated with the strong La Nina. This led to changes in the ocean density and sea surface elevation which propagated through the Indonesian Seas and along the west coast. This remote forcing contributed to its southward strengthening.
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Why is it important?
The 2011 marine heatwave led to notable changes and shifts in the coastal marine ecosystems, including deaths in seagrass, invertebrates, and fish populations and coral bleaching. The warming was mostly caused by an unusual strengthening of the Leeuwin Current.
Perspectives
This study introduced me to marine heatwaves and their devastating impacts on coastal ecosystems. Since then, a number of major events have occurred around Australia, from the Great Barrier Reef in 2016, 2017, the North West Shelf in 2016, to the Tasman Sea in 2016. Understanding what causes these events is of great importance, so that we can predict when and where these events occur and their impacts on marine ecosystems.
Dr Jessica A. Benthuysen
Australian Institute of Marine Science
Read the Original
This page is a summary of: Spatial patterns of warming off Western Australia during the 2011 Ningaloo Niño: Quantifying impacts of remote and local forcing, Continental Shelf Research, December 2014, Elsevier,
DOI: 10.1016/j.csr.2014.09.014.
You can read the full text:
Resources
Elsevier AudioSlides
5 min video
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5 min talk
Freshening anomalies in the Indonesian throughflow and impacts on the Leeuwin Current during 2010–2011
During the 2010–2011 La Niña and Ningaloo Niño, excessive precipitations in the Maritime Continent and Indonesian-Australian Basin caused surface waters to freshen by 0.3 practical salinity unit in the southeast Indian Ocean. The low-salinity anomalies are observed to be carried westward by the Indonesian throughflow and the South Equatorial Current and transmitted into the poleward flowing eastern boundary current, the Leeuwin Current, along the Western Australian coast. Low-salinity anomalies contribute to about 30% of the anomalous increase of the southward Leeuwin Current transport during the evolution of the 2010–2011 Ningaloo Niño, resulting in unprecedented warming off the coast of Western Australia. Episodical freshening of the Leeuwin Current has been observed at the Rottnest coastal reference station of Western Australia during extended La Niña conditions over the past several decades; low-salinity anomalies at the station during the 2010–2011 Ningaloo Niño are comparable with strong historical events.
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