A perfect storm of factors produced by unprecedented oceanographic conditions in 2016 led to a mass coral bleaching in the northern Great Barrier Reef. The observation was made by researchers from Belgium’s Université Catholique de Louvain and Australia’s James Cook University (JCU).
The research team from JCU had conducted an aerial survey of the northern Great Barrier Reef in 2016 that showed 90 percent of reefs in some of these parts was extremely bleached. However, the severe coral bleaching in these areas during the summer of 2016 was surprising. This is because previously, even in extremely warm years with a summer El Niño event such as the one that took place in 1998, there was no coral bleaching in such a mass scale in the Torres Strait. Moreover, the northern Great Barrier Reef had only small to moderate amount of bleaching.
According to Phys.org, the researchers said that the satellite data showed that the 2016 El Niño heating started in the Gulf of Carpentaria. Subsequently, areas of water reached an exceptional high of 34 degree Celsius and then flowed south to the Great Barrier Reef and east to the Torres Strait reefs. The warm water stayed for a long time in the two areas that increased the thermal pressure on the coral. All of these factors made it possible for the local solar heating to proceed unhindered.
"Examining surface currents suggests that the North Queensland Coastal Current in the Coral Sea, which would normally flush and cool the Northern Great Barrier Reef, actually did the opposite,” JCU's Professor Eric Wolanski said. “It reversed course and brought very warm water to the Northern Great Barrier Reef."
Professor Wolanski added that all the processes in tandem made it the perfect thermal storm. The professor also stated that the research team presented their best informed attempt in their paper published in Estuarine, Coastal and Shelf Science to unveil the mechanisms involved in causing the event. They did this with the help of the information present about water circulation in and around northern Great Barrier Reef/Torres Strait region as well as the available oceanographic data.