Structural Climate Drivers of Global Coral Bleaching.

Area of Science:

• Marine Biology
• Climate Science
• Oceanography

Background:

• Mass coral bleaching is a key indicator of climate change impacts.
• Traditional assessments of bleaching struggle to explain its persistence and regional variations.
• Surface thermal anomalies and strong El Niño phases are insufficient explanations.

Purpose of the Study:

• To investigate the structural mechanisms behind the spatial and temporal evolution of mass coral bleaching.
• To identify a regime shift in coral bleaching patterns.
• To propose a framework for understanding and predicting bleaching risk.

Main Methods:

• Analysis of long-term datasets (1993-2020) including ocean temperature, bleaching alerts, ENSO indices, coral-algal cover, and subsurface thermal profiles.
• Development of the "Structure-Pathway-Response" framework.
• Identification of heat-retention regimes.

Main Results:

• A regime shift from episodic to chronic thermal exposure in coral bleaching.
• Reduced dependence of bleaching on El Niño-Southern Oscillation (ENSO) intensity.
• Identification of heat convergence, poleward subsurface heat transport, and isotherm deepening as key risk factors.
• Two dominant heat-retention regimes identified: current-deflection and thermal-stacking.

Conclusions:

• Sustained ocean warming is eroding coral thermal thresholds.
• Surface monitoring alone is inadequate; subsurface processes significantly influence bleaching risk.
• Region-specific, thermodynamically informed early-warning systems are needed.
• Managing heat pathways and protecting thermal refugia are crucial for coral reef resilience.