Reconstructing ultra-high resolution climate variability and symbiont bleaching in tropical corals: from past to present (EPIBleach)

• Applicants: Dr. Jan Fietzke; Professor Dr. Martin Frank
• Subject Area: Geology ; Oceanography
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 468679331

The currently increasing occurrence of bleaching events in tropical coral reefs endangers an ecosystem that existed in quasi-stable conditions for thousands of years or more, and threatens the lifelihood of tropical communities. Even though rising seawater temperature is a key driver for coral bleaching, there are indications that competing environmental stressors can alter symbiont tolerance to climate change and thus coral survival, and that there are different sensitivities among coral species and geographic regions. Additionally, the observational record of bleaching events is limited both in space and time, as it cannot be detected by remote sensing. Here using a multi-proxy and multi-species coral approach, we will establish geochemical proxies of coral bleaching using field-collected and cultured corals grown through bleaching events, and will reconstruct the environmental conditions (i.e. seawater temperature, salinity, pH, nutrient loading) leading into and out of such events in the field. This multi-proxy approach will then be applied to fossil corals dated within the warm periods of the Holocene, the last Interglacial, the Pliocene, and the Eocene, utilizing exceptionally well preserved corals from collaborators and from museum collections in the USA, Switzerland, and the UK. Fossil corals were selected from within the same genera and families that have been calibrated in modern corals. Our reconstructions will follow bi-monthly to sub-monthly resolution, using a combination of solution and laser ablation analytical methodologies, to reconstruct the environmental variability during these past warm periods on Earth and to capture the full geochemical signal of bleaching events applying our multi proxy approach established in modern and cultured corals. As a result, our reconstructions will constitute two major contributions to the SPP2299: one by reconstructing ultra-high resolution climate variability from tropical regions, which will provide novel sub-seasonal marine records not previously explored, especially for the Eocene and the Pliocene, and two by exploring the link between environmental/climatic change and reconstructed bleaching events in the past, as a function of background climate (e.g. Earth’s temperature), tropical coral species richness and coral diversification.

• 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
• Co-Investigator: Dr. Eleni Anagnostou, Ph.D.