Far away, so close: cause of massive marine heatwave found in distant ocean

In 2010-2011 an anomalous, but recurring ocean circulation condition in the Pacific Ocean – known as ‘La Niña’ - caused a massive ocean heatwave more than 10,000 km away, in the Indian Ocean along Australia’s western coast. This had dire ecological consequences from widespread coral bleaching to fish kills, including in two UNESCO Marine World Heritage Sites. The link between these two distant climate and marine events in the Pacific and Indian Oceans was established through collaborative researarch by U.S. and Australian oceanographers, using data collected under the Global Ocean Observing System (GOOS) and in particular, from its flagship observation programme – the international Argo global array of profiling floats.

Record breaking sea surface temperatures were observed in February and March 2011, during the Austral summer, off the west coast of Australia. These were more than 3ºC above long-term seasonal averages, and exceeding 5ºC for a two-week period at the peak of the event. Water temperatures affect the growth, survival, abundance and distribution of most marine species. Many marine organisms cannot adjust to such rapid short-term temperature rises, which can be harmful or even lethal, causing coral bleaching, widespread fish mortality, and can have potentially catastrophic impacts on marine ecosystems.

The marine heatwave had profound impacts on marine ecosystem structure in this global biodiversity hotspot. Two UNESCO World Heritage Sites are found in the area: Shark Bay, home to the largest sea-grass beds in the world and five species of endangered mammals, and Ningaloo Coast, which includes one of the longest near-shore reefs in the world. Both were impacted, and in addition, key fisheries, seafood and aquaculture industries to Australia were hit. In some instances – including the lucrative abalone industry – stock has never recovered. The impact to Australia’s economy and sources of food to both Australians and Asians (via export) were widely felt.

This extreme event in the Indian Ocean – now termed ‘the Ningaloo Niño’ because of its proximity to the Ningaloo World Heritage Site - was driven by unusual features in the Leeuwin Current. The Leeuwin Current is the longest boundary current in the world characterized by warm ocean water, flowing from the sea north of Australia, southwards along the western coast of Australia. It is the driving force creating the conditions for the unique marine biodiversity in this global biodiversity hotspot, and was affected by the extreme ocean and atmospheric conditions in the Pacific and Indian Ocean during the 2010-2011 La Niña (See map).  

The Ningaloo Niño is a sharp reminder that we are all connected through the ocean, and that far-away climatic events have an impact on marine conditions more than 10,000km away in a different ocean. ‘Understanding the factors that influence the formation of events like the 2011 Ningaloo Niño is a vital first step in preparing for impacts from extreme warming events in the future,’ said lead researcher, Dr. Ming Feng of Australia’s CSIRO. This is especially true in the context of a warming ocean.

Understanding the connection between such distant events would not be possible without initiatives like the Global Ocean Observing System (GOOS). Led by the Intergovernmental Oceanographic Commission (IOC-UNESCO), it is the global platform for international cooperation that collects real time data on the physical state as well as the biogeochemical profile of the world's oceans, provided by ships, buoys, subsurface floats, tide gauges and satellites. Ocean data observed simultaneously in different oceans, by countries from every continent allow scientists to find global tele-connections in air and ocean weather like the Ningaloo Nino. GOOS provides the mechanism to facilitate collaborative oceanographic research between countries in the world’s oceans, and especially for societal benefit.

One of the flagship programs for GOOS is the international Argo project - a collaborative partnership of more than 30 nations from all continents, all working together to provide a seamless global array of over 3,000 subsurface profiling floats measuring temperature, salinity, and depth during every ascent to the sea surface.

The results of the collaborative research on this extreme 'Ningaloo Niño' event were published in Nature Scientific Reports in February 2013. ‘Nature always finds a way to surprise us and the Ningaloo Niño is just the latest episode in this continuing saga’ said co-author Dr McPhaden of the US Government’s NOAA. ‘This is research that matters to society because it tells us that what happens in your backyard can be influenced by events happening in far away places and at times in the distant past.’

Understanding our climate and ocean is possible through sustained observations and monitoring. Without the Argo data and collaboration under GOOS for the collection and sharing of ocean data, these research findings published less than two year after the event, would have been difficult. Ultimately, improved ocean observations help society to better prepare, respond and adapt to future extreme events that have serious ecological, economic and social implications.

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Sources: Commonwealth Scientific and Industrial Research Organization (CSIRO) and National Oceanic and Atmospheric Administration (NOAA)