This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The strong El Niño currently under way in the Pacific Ocean raises the specter of marine heat waves and coral bleaching once again threatening Australia's iconic Great Barrier Reef. And now new research has revealed the complex interplay of atmospheric patterns and weather systems thousands of kilometers apart that can combine in a recipe potentially fatal for coral reefs.
Sea-surface temperatures in the Coral Sea off northern Queensland often increase during periods known as the "doldrums," characterized by weak winds, reduced cloud cover and dry, descending air. These conditions are unusual for the humid tropics, where we would typically expect plenty of cloud cover, thunderstorms and rainfall. Lara Richards conducted the research as a Ph.D. student with the ARC Center of Excellence for 21st Century Weather at Monash University, before joining the University of Reading as a research fellow.
The paper is published in the journal Weather and Climate Dynamics. "We wanted to understand why these doldrums form and what makes some last longer," Richards said. "When doldrums hang around, the ocean remains in a heating phase for longer, which can produce rapid increases in temperature and contribute to coral bleaching." The doldrums can happen at any time, and are not caused by the El Niño-Southern Oscillation (ENSO).
Nevertheless, an active El Niño raises the level of background threat, and a prolonged spell of doldrums during a strong El Niño phase could contribute to the development of a marine heat wave and increase the risk of harmful mass coral bleaching. Normally, the easterly trade winds naturally cool the waters around the reef, stirring the upper ocean and helping heat escape its surface. But when doldrum conditions persist, this natural cooling process is suppressed.
The relationship between weak winds, reduced cloud cover, ocean heating, and coral bleaching is well understood, but scientists have struggled to fully explain why doldrums themselves occur, including why some pass quickly and others persist. New work led by 21st Century Weather researchers based at Monash University and the University of Melbourne has tackled that challenge to produce our most comprehensive understanding to date of the weather conditions that can produce sustained doldrums and increase the risk of a mass bleaching event. Crucially, contributing author Dr.
Yi Huang of 21st Century Weather and the University of Melbourne said the team focused on interactions between weather systems over the tropics and the mid-latitudes. "A lot of previous research has focused on what happens locally over the Great Barrier Reef. This study looks beyond the local weather to understand how much larger weather systems interact to create those conditions," Huang said.
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