MELBOURNE, Jan. 19 (Xinhua) -- Periods of calm, windless weather known as "doldrum days" are increasingly driving mass coral bleaching on Australia's Great Barrier Reef, new research revealed on Monday.
The study analyzed nearly three decades of weather data during the coral bleaching season and linked extended breaks in the trade winds, which normally help cool reef waters, to spikes in ocean temperature and widespread coral stress, said a statement from Australia's Monash University.
The study, published by the European Geosciences Union, found that when large planetary atmospheric waves are present, this can lower atmospheric pressure and disrupt the trade winds, increasing the chances of doldrums forming.
In particular, losing these classic trade winds during December and April, respectively, means less ocean cooling and could contribute to a build-up of early summer heat stress and the persistence of heat later into the season, researchers said.
Trade winds act like nature's air conditioner for the reef, said Lara Richards, lead researcher and PhD candidate in the Australian Research Council Center of Excellence for the Weather of the 21st Century, which led the research with Monash University.
"When they fail, the ocean heats up quickly, and corals suffer," Richards said, adding that understanding these patterns could help scientists better predict and reduce future bleaching impacts.
Researchers found that years with mass bleaching events had more calm, clear days during the hottest months and fewer strong trade wind days between December and April, allowing heat to accumulate and persist longer, creating ideal conditions for marine heatwaves.
When the reef suffers mass coral bleaching, doldrums happen more often and last longer, said Professor Steven Siems from the School of Earth, Atmosphere and Environment at Monash University.
The research highlights how missing cooling events at the edges of the season can turn an ordinary year into a bleaching year, Siems said.
The study urges closer monitoring of atmospheric patterns, warning that as climate change continues to disrupt weather systems, trade winds are becoming increasingly vital to reef protection. ■
