Enhanced upwelling from internal waves in a warming ocean cools a shallow island reef

As ocean temperatures rise, understanding the cooling role of internal waves is crucial for reef preservation. This study uses high-resolution, nonhydrostatic simulations at Dongsha Atoll in the South China Sea to explore bottom temperature changes affecting benthic ecosystems under seasonal and climate scenarios for 2020 and 2100. Climate-induced surface warming increases stratification, altering internal wave propagation. Our findings show that internal waves transport cooler, deeper waters into shallow areas, reducing warming by up to 2.3°C relative to conditions without waves, while deeper areas experience relative warming. Enhanced stratification in warmer scenarios enhances wave-driven cooling by up to 0.5°C in shallow zones. Temporal fluctuations in bottom temperature due to internal waves are also enhanced in a warmer, more strongly stratified ocean, potentially increasing by up to 1.4°C over current variability. However, net warming by 2100 is projected at up to 2.8°C in shallow areas and 0.9°C in deeper regions under SSP5-8.5. These findings highlight the complex interactions between climate warming and internal wave effects on reef thermal environments, suggesting that areas with strong internal wave activity could serve as thermal refugia. Nonetheless, the overall trend points to continued warming, highlighting the urgent need for global climate action to mitigate ocean warming.