Climate and environmental change in the Andaman Sea since the late Little Ice Age: sea surface temperature, hydroclimate, and coral response to thermal stress in the northeastern Indian Ocean

Human-induced climate change has significantly increased ocean temperatures, exposing tropical reef ecosystems to repeated and intense marine heatwaves that drive widespread coral bleaching. Recent mass global coral bleaching events have been attributed to the interactions between long-term warming and modes of tropical climate variability. However, understanding how these interactions influence coral responses to thermal stress over time is hindered by the lack of reef-scale temperature and hydrological observations, as well as a lack of extensive ecological reef monitoring spanning multiple centuries. Geochemical records obtained from coral carbonate skeletons are excellent proxies for extending instrumental observations and can be useful tools to identify how corals respond to thermal stress. This thesis presents newly developed monthly records of skeletal trace elements and stable isotopes from massive Porites spp. corals at Ko Racha Yai (Thailand), southern Andaman Sea in the northeastern Indian Ocean, a prominent reef refuge site from global warming. These geochemical records were generated to reconstruct temperature, hydroclimate, and coral response to thermal stress since 1774. Overall, this thesis demonstrates that existing observations, ecological reef monitoring, palaeorecords, and model simulations do not capture the full range of interactions between climate change and tropical climate variability, and their combined impacts on coral response to thermal stress.