Trade wind regimes during the Great Barrier Reef coral bleaching season

Abstract. The trade winds over the Great Barrier Reef (GBR) dominate the local weather in the region, bringing cooler and drier air over the Reef, which promotes ocean cooling. The absence of the trade winds is often marked by periods of weaker winds and higher humidity, known as the doldrums, which cause ocean temperatures to spike and can develop into marine heatwaves that lead to coral bleaching. As the shallow waters of the GBR are strongly tied to the local meteorology, studying the evolution and structure of the trade winds during the austral warmer months is essential for understanding the development of thermal bleaching events. Through a K-Means cluster analysis on reanalysis soundings at Davies Reef from December–April 1996–2024, we find the formation of the doldrums is linked to the passage of a Rossby-wave train over eastern Australia. Years with mass thermal bleaching are linked with more doldrums days and weakened trade winds during December and April which can promote early-summer warming and allow warmer temperatures to persist later into the season.