A ‘perfect storm’ of conditions is said to be the cause of bleaching of the Great Barrier Reef in Australia.
This ‘perfect storm’ isn’t an actual storm, but a number of factors occurring at the same time caused the bleaching. According to researchers from James Cook University and the Université catholique de Louvain, Louvain-la-Neuve, Belgium, warm years during a summer El Nino event isn’t the only reason as previous such warm years haven’t caused massive coral bleaching.
Analysis of a 2016 aerial survey of the northern Great Barrier Reef showed that 90 per cent of reefs in some of these areas were severely bleached. Satellite data indicated that for the El Nino of 2016, heating started in the Gulf of Carpentaria, with patches of water reaching an exceptionally high 34 C. The water then flowed east onto the Torres Strait reefs and south to the Great Barrier Reef.
The ‘residence time’ of the very warm water in the Torres Strait and the Northern Great Barrier Reef was exceptionally long, which increased the thermal stress on the coral. All of these factors enabled local solar heating to proceed unrestricted.
Normally the North Queensland Coastal Current in the Coral Sea would flush and cool the Northern Great Barrier Reef, but that didn’t happen and actually the opposite happened wherein the course was reversed and very warm water was dumped into the Northern Great Barrier Reef. These processes together made it the perfect thermal storm.
JCU’s Professor Eric Wolanski says “What we presented is our best-informed attempt to reveal the mechanisms involved in causing the event, based on the available oceanographic data combined with the existing body of knowledge on the water circulation in and around the Torres Strait/Northern Great Barrier Reef region.”