Abstract
Tropical coral reefs are threatened by rising seawater temperatures. However, cold-water intrusions to coral reefs by oceanic processes such as upwelling or internal waves, which propagate along the thermocline, can offer refugia from global warming. How reef temperatures and coral responses vary in such locations remains poorly understood due to limited in-situ observations. We present monthly subsurface temperature and coral response records based on coral skeletal geochemistry from the Andaman Sea, a known thermal refugia. Coral Sr/Ca-temperature indicates subsurface reef cooling varied at interannual to decadal timescales, driven by large-scale wind and thermocline changes, and was most pronounced during the combined positive Indian Ocean Dipole and El Niño event of 1997/98. Coral carbon isotopes indicate relative shifts from autotrophy to heterotrophy during most coral bleaching events observed in the Andaman Sea, except during the 1998 event when we found strong and widespread subsurface reef cooling by thermocline shoaling leading to enhanced influence of internal waves. Our results indicate tropical climate modes such as the Indian Ocean Dipole and the El Niño-Southern Oscillation controlled the strength and spatial distribution of thermal stress mitigation by oceanic processes through time, suggesting some coral reef refugia will be variable under future climate change.
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Acknowledgements
We thank S. Pape and H. Kuhnert and his team (MARUM, University of Bremen, Germany) for analytical support, P. Witte (Faculty of Geosciences, University of Bremen, Germany) for SEM analysis, C. C. Ummenhofer (Woods Hole Oceanographic Institution, US) for guidance using the ORAS5 dataset and discussion on thermocline analysis, J. Tanzil (National University of Singapore, Singapore) for discussion on coral bleaching and ocean-climate dynamics in the Andaman Sea and temperature logger data, N. Phongsuwan (Phuket Marine Biological Center, Thailand) for providing temperature logger data, R. P. Dunne (West Briscoe, UK) and B. E. Brown (Newcastle University and University of the Highlands and Islands, UK) for guidance in downloading and processing DHW with the NOAA CRW dataset, and O. Knebel (MARUM, University of Bremen, Germany) for discussion on statistical analysis. The coral core was exported under CITES permits AC.0510.2/3924 and PWS2019-AU-002875. We thank the Department of Marine and Coastal Resources (Thailand), Department of Fishery (Thailand), Piya Koeysin and Dr. Voranop Viyakarn, for permits.
Funding
Open Access funding enabled and organized by Projekt DEAL. This study was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project number 468644633 (T.F.) – SPP 2299/Project number 441832482. M.W. acknowledges funding by the DFG – Project number 468679988 – SPP 2299/Project number 441832482. S.C. acknowledges support by the Office of the Ministry of Higher Education, Science, Research, and Innovation, Thailand under the Reinventing University System/Visiting Professor Program.
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Camelia, H., Felis, T., Hargreaves, J.A. et al. Tropical climate modes control strength and distribution of thermal stress mitigation in a coral reef refugia.
Sci Rep (2026). https://doi.org/10.1038/s41598-026-52941-6
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DOI: https://doi.org/10.1038/s41598-026-52941-6
Source: Ecology - nature.com
