El Nino – Southern Oscillation
Year: 2009
Type: article
Abstract: El NioSouthern Oscillation (ENSO) is the dominant global mode of year-to-year (interannual) climate variability. It is a major contributor to Australias climate, and affects Australias Exclusive Economic Zone (EEZ) marine waters to differing degrees around the coast. ENSO has a strong and very significant effect on the intensity of the southward flowing Leeuwin Current, and Australias west coast waters, being transmitted by ENSO-generated planetary waves that propagate from the western Pacific Ocean through the Indonesian Throughflow which become trapped along Australias west coast. The ENSO signal in the Leeuwin Current is further transmitted along the south coast of Australia. ENSO is observed as a weaker signal in the southward flowing East Australian Current along Australias east coast.There have been several published studies of the effects of ENSO on marine biota and seabirds. Along Australias west coast, for example, La Nia events have been found to assist the transport of western rock lobster (Panulirus cygnus) larvae, while El Nio events are better for scallops. Further, ENSO is also known to disrupt seabird spawning and the seasonal migration of whale sharks (Rhincodon typus) in this region. The strength of the Leeuwin Current also influences recruitment of pilchard, whitebait, Australian salmon and herring along Australias south coast. To the east, there is evidence for a greater abundance of black marlin (Makaira indica) off northeast Australia during El Nio years, greater likelihood of unusually warm waters leading to coral bleaching during the late summer-autumn of the second year of El Nio events in the Great Barrier Reef, and loss of giant kelp ((Macrocystis pyrifera)off the east and south coasts of Tasmania associated with major El Nio events. Along Australias north coast, enhanced catches of banana prawns (Panaeus merguiensis) in the Gulf of Carpentaria during high rainfall/river flow La Nia years have also been reported.Based on the suite of IPCC AR4 model simulations forced with projected increases in greenhouse gases, the multi-model mean represents an overall weak shift in the background state towards future climate conditions which have been described as El Nio-like. While there is 80% consensus across the AR4 models for an El Nio-like future climate (which could be interpreted as a shift in the mean), there is no consistent indication of future changes in ENSO amplitude or frequency. The pragmatic approach is to assume that ENSO events will continue as a source of significant interannual climate anomalies affecting the marine environment. Future ENSO events will be superimposed on 1) warmer sea surface temperatures than present making El Nio impacts associated with unusually warm waters (e.g., coral bleaching) more severe, 2) more intense (though maybe fewer) tropical cyclones causing increased physical destruction of, for example, coral reef structures during La Nia events, c) more extreme rainfall (though changes in average rainfall are unclear), with more intense drought periods (exacerbated by warmer air temperatures) during El Nio events and more intense high rainfall events with increased freshwater/sediment flow to coastal environments during La Nia events, and d) higher sea levels which, as well as reducing land areas of island and cays (important nesting grounds for marine reptiles and seabirds), will increase impacts of tropical and extra-tropical cyclones. We expect a reduction in the overall intensity of the Leeuwin Current due to the projected change in background state towards a shallower thermocline in the Warm Pool region to the north of Australia unless this is offset by changes in the alongshore winds and global hydrological cycle.Moving anti-clockwise around Australias coast from the northeast, we have high confidence that ENSO affects Australias northeast and north coast waters, medium/high confidence that ENSO affects Australias west coast wa
Institution: University of Tasmania
Language: Spanish
Subfield: Global and Planetary Change
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W1569459551