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

Figure 1: NOAA Coral Reef Watch 5 km Bleaching Alert Area Year-to-date Maximum (5 Oct. 2022), maximal heat stress on one pixel within the beginning of 2022 and 5 Oct. 2022; “Watch” means light heat anomaly Degree Heat Wave (DHW) >0, “Warning” means possible bleaching DHW < 4, “Alert Level 1” means significant bleaching DHW 8 .

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 livelihood 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. These proxies will be applied to fossil corals to reconstruct past bleaching events and the environmental conditions (i.e. seawater temperature, salinity, pH, nutrient and sediment loading) leading into and out of such events in the geologic record (Fig.1).

Fossil corals were selected from within the same genera and families which will be calibrated using modern corals. Our reconstructions will follow sub-seasonal 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:

  • Reconstruction of ultra-high resolution climate variability from tropical regions, which will provide novel sub-seasonal marine records not previously explored, especially for the Eocene, the Pliocene, and the last Interglacial.
  • Exploration of the link between environmental/climatic change and reconstructed bleaching events in the past, as a function of background climate, tropical coral species richness, and coral diversification.
Figure 2: Key aspects of the EPIBleach Project