Understanding Systems and How They Change

The “IndOC-E II SPP 2299” project contributes to a better understanding of tropical marine climate variability and its impacts on coral reef ecosystems in a warming world. It does this by quantifying climatic and environmental changes during the warming from the preinstrumental period to the early 21st century on societally relevant timescales. The project reconstructs marine climate and environmental changes in the northeastern Indian Ocean since the late Little Ice Age at ultra-high resolution by analyzing 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 a previous phase of the project, a site that was not significantly affected by marine heat waves due to the moderating effect of internal-wave-induced cooling provided proxy records of sea surface temperature and hydrology (hydroclimate) back to the year 1774, based on paired measurements of Sr/Ca and oxygen isotopes, with the potential for reconstructing Indian Ocean Dipole events. In the current phase of the project, another site that remains exposed to the unabated effects of heat waves is being studied in detail to provide proxy records of coral response to thermal stress events back to the early 1800s, based on anomalous signatures in measurements of Sr/Ca, oxygen isotopes, Mg/Ca, stable carbon isotopes, and growth patterns. This study examines the history of stress response of a centuries-old coral colony that died in 2010 during one of the most severe coral bleaching events in the Andaman Sea, and sets it into context with the local thermal history of a different colony that was not severely affected by heat waves and survived the event. These reconstructions enable the study of how various El Niño flavors, the Indian Ocean Dipole, tropical volcanic eruptions, and internal waves have interacted in modulating variability and extremes of Andaman Sea temperatures and hydrology since the late Little Ice Age, with implications for coral growth and resilience. These reconstructions make it possible to investigate whether corals in the Andaman Sea were exposed to thermal stress events in past centuries and whether an environmental memory resulting from past extreme warming events in the northeastern Indian Ocean, such as the very strong 1877/78 El Niño event, led to higher temperature tolerance during thermally induced stress events in recent decades.

Key figures: 

• Funding provider: German Research Foundation (DFG)

• Duration: 2026–2029

• Project coordinator: Dr. Thomas Felis

• Affiliation/institute: MARUM – Center for Marine Environmental Sciences