New study reveals hidden ocean heatwaves threatening South China Sea ecosystems
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Subsurface MHW impacts on deep ecosystems in the SCS
view moreCredit: Ning Cao
The South China Sea (SCS), a vital marine region supporting rich biodiversity, productive fisheries, and extensive coral reefs, faces growing threats from marine heatwaves (MHWs). While surface MHWs have drawn attention, subsurface events—intense warming below the ocean surface—during boreal winter have been less studied, yet they can disrupt deeper-dwelling species and ecosystem stability in this semi-enclosed sea.
A research team from Guangdong Ocean University has uncovered the key mechanisms driving these winter subsurface MHWs in the SCS, pinpointing the northeastern basin west of the Luzon Strait as a persistent hotspot. Their analysis shows that heat transport from the Kuroshio through the Luzon Strait, combined with swirling mesoscale eddies, significantly amplifies subsurface warming at depths of 70–300 m, making events deeper, more intense, and more frequent than in other parts of the sea. The study has been recently published in the journal Atmospheric and Oceanic Science Letters.
Using long-term high-resolution ocean reanalysis data spanning 1994–2023, the scientists mapped the patterns and vertical structures of these hidden heatwaves. They found that MHW intensity often peaks at a depth of around 130 m, with the strongest zones shifting northeastward as depth increases. In the Luzon Strait–influenced area, subsurface MHWs penetrate deeper and occur more often compared to the broader SCS.
Heat budget calculations revealed that ocean currents dominate the process: steady vertical movement brings heat downward, while horizontal flows from the Luzon Strait counteract winter surface cooling. Crucially, anticyclonic eddies—those spinning clockwise with negative vorticity—trigger downwelling, trapping and enhancing warm water below the surface during peak years.
“These findings highlight the northeastern South China Sea as a winter MHW hotspot and provide a basis for assessing ecological risks to vulnerable marine ecosystems,” says Dr. Ning Cao, the corresponding author of the study.
This local focus is especially relevant for the SCS, where subsurface warming can stress fisheries by affecting fish stocks at greater depths and threaten coral reefs through prolonged thermal stress on deeper layers. By clarifying the role of Luzon Strait inflow and eddies, the work offers valuable insights for improved prediction and monitoring of these events in this economically and ecologically critical region.
In the future, the researchers aim to refine models incorporating these dynamics for better forecasting of subsurface MHWs, helping support sustainable management of the SCS’ marine resources amid ongoing climate pressures.
Journal
Atmospheric and Oceanic Science Letters
