The urgent push to protect the iconic Great Barrier Reef of Australia from catastrophic events of mass coral bleaching received a significant boost, with a new investigation from Monash University identifying wind patterns as a fundamental cause.
Until now, the cause of rising ocean temperatures that lead to coral bleaching was unclear and was often linked to El Niño.
But analysis of more than three decades of atmospheric time series conducted by Monash University revealed the role of the east trade winds, responsible for regulating reef temperature.
It was a case study of a mass bleaching event affecting 91% of the reef in February 2022, the fifth in eight years, which provided the finding for the lead researcher and PhD candidate in atmospheric sciences at Monash, Lara Richards.
“Our investigation identified that it was the collapse of the east trade winds that drastically altered near-surface ocean temperature,” says Lara Richards.
“During a three-week period, we observed warming of the ocean in this zone by almost 2°C to 30.5°C, as the absence of the trade winds allowed a reduction in cloud cover, an increase in solar radiation and the lack of cooling by evaporation,” she adds.
“After the trade winds were restored, the warming ended abruptly and the ocean temperature cooled by 1°C in 48 hours, as evaporative cooling effectively tripled.”
The findings, detailed in a peer-reviewed study published in the scientific journal Scientific Reports, highlight the exacerbated impact of local weather on coral reefs and provide previously unseen clues to help combat the impact of coral bleaching on the reef.
Based on data from the Davies Reef Automatic Weather Station of the Australian Institute of Marine Science, located at Davies Reef, 100 kilometres northeast of Townsville, Monash researchers compared three decades of air and ocean temperature, humidity, wind speed and direction, and wave and tide patterns.
In identifying the cause of the major episodes of ocean temperature rise that trigger coral bleaching, the research also helps dispel myths surrounding links to El Niño.
“People tend to associate coral bleaching on the Great Barrier Reef with El Niño, which we can now show to be incorrect,” says Richards.
“That is why we were looking at 2022 in particular, because it was the first bleaching on the reef during a La Niña phase,” she explains.
“Thus, we were able to show that, since bleaching can occur during both El Niño and La Niña, it was the change in weather conditions that caused the bleaching.”
Mass coral bleaching events are catastrophic for the biodiversity of the Great Barrier Reef, a UNESCO World Heritage site, killing corals and threatening fish and other organisms through habitat loss.
As a major tourist destination, reef loss would also risk about 64,000 jobs and $56 million in revenue.
“The Intergovernmental Panel on Climate Change identified coral reef loss as a major risk for Australia, so understanding it is essential to forecast and respond,” says Richards.
“Now that we understand the conditions that can lead to bleaching events, we will be able to predict where and when they will occur and take steps to respond and mitigate their impacts,” concludes.
