Climate and environmental change in the Andaman Sea since the late Little Ice Age: History of coral response to thermal stress at a northeastern Indian Ocean heatwave site (IndOC-E II)

• Applicant: Dr. Thomas Felis
• Subject Area: Geology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 468644633

This project contributes towards a better understanding of tropical marine climate variability and its impact on coral reef ecosystems in a warming world, by quantifying climatic and environmental changes during the warming from the pre-instrumental period to the early 21st century on timescales relevant for society. These are major aims of the Priority Programme “Tropical Climate Variability and Coral Reefs” (SPP 2299). The project reconstructs marine climate and environmental change in the northeastern Indian Ocean since the late Little Ice Age at ultra-high resolution, by analysing isotopic and geochemical proxies in shallow-water coral skeletons. The project generates reconstructions of sea surface temperature, hydrology (hydroclimate), and coral response to thermal stress back to the early 1800s at monthly resolution from Porites corals of the southern Andaman Sea (Thailand). In the previous project phase (IndOC-E), a site not strongly affected by marine heatwaves because of the mitigating effect of cooling by internal waves provided proxy records of sea surface temperature and hydrology (hydroclimate) back to the year 1775, based on paired measurements of Sr/Ca and 18O, with potential for reconstructing Indian Ocean Dipole events. In the second project phase (IndOC-E II), another site experiencing the unabated influence of heatwaves will be studied in detail to provide a proxy record of coral response to thermal stress events back to the early 1800s, based on anomalous signatures in measurements of Sr/Ca, 18O, Mg/Ca, 13C, and growth patterns. The history of stress response of a centuries-old coral colony that died in 2010 during one of the most severe coral bleaching events on record in the Andaman Sea will be studied, and set into context with the local thermal history derived in the previous project from a different colony not strongly affected by heatwaves that survived this event. The reconstructions will enable to study the interplay of different El Niño flavours, the Indian Ocean Dipole, volcanic eruptions, and large amplitude internal waves in modulating variability and extremes of Andaman Sea temperatures and hydrology since the late Little Ice Age, with implications for coral growth and resilience. The reconstructions will enable to explore if Andaman Sea corals were exposed to thermal stress events during past centuries and if environmental memory, resulting from extreme northeastern Indian Ocean warmings of the past such as the very strong 1877/78 El Niño event, lead to higher temperature tolerance during thermally-induced stress events of recent decades.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2299: Tropical Climate Variability and Coral Reefs. A Past to Future Perspective on Current Rates of Change at Ultra-High Resolution
• International Connection: Thailand
• Cooperation Partner: Professorin Dr. Suchana Chavanich