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UndeRstanding coral thErmal bleaching threSholds during past InterglacIaL extremes: Insight into thermal StrEsses DyNamics on tropical Coral reef Ecosystems (RESILIENCE)

English title UndeRstanding coral thErmal bleaching threSholds during past InterglacIaL extremes: Insight into thermal StrEsses DyNamics on tropical Coral reef Ecosystems (RESILIENCE)
Applicant Spezzaferri Silvia
Number 201106
Funding scheme Project funding
Research institution Département des Géosciences Université de Fribourg
Institution of higher education University of Fribourg - FR
Main discipline Geology
Start/End 01.10.2021 - 30.09.2025
Approved amount 952'218.00
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All Disciplines (2)


Keywords (4)

foraminifera; corals; geochemistry; temperature thresholds

Lay Summary (Italian)

Le barriere coralline sono ecosistemi ad alta biodiversità, sottoposti a molteplici stress, incluso il riscaldamento globale, che potrebbero compromettere la loro sopravvivenza. Uno dei segni visuali di stress è lo sbianchimento dei coralli dovuto alla perdita dei simbionti. L’aumento recente in intensità e durata di questi eventi ha seriamente compromesso la resilienza delle barriere coralline, e un loro incremento è predetto per gli anni a venire. Il migliore approccio per predirre l’impatto del riscaldamento globale su questi ecosistemi è di investigare simili eventi nel passato. Purtroppo lo sbiancamento non puo’ essere osservato in coralli fossili, e l’archivio paleoclimatico in sedimenti profondi adiacenti a barriere coralline ci puo dare informazioni rilevanti su eventi del passato.
Lay summary

Il nostro obiettivo é di valutare ampiezza e frequenza di periodi interglaciali caratterizzati da temperature anomale che possono avere causato lo sbiancamenti nei coralli nel passato e di valutare se l’aumento di nurienti nel mare ha contribuito a questo fenomeno. Useremo sedimenti di acque basse recuperati da barriere coralline e sedimenti di acque profonde per ottenere una riscostruzione paleoceanografica globale nei tropici. Le paleo-temperature calcolate con metodi geochimici su coralli e foraminiferi serviranno ad estrarre i segnali di frequenza e ampiezza delle temperature estreme dal Presente fino allo stadio isotopico MIS31 (Pleistocene) che hanno superato i limiti termici per lo sbiancamento dei coralli. La nostra ricerca darà un importante contributo per quantificare le temperature anomale passate per una potenziale previsione di un futuro scenario.

Direct link to Lay Summary Last update: 09.07.2021

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Associated projects

Number Title Start Funding scheme
165131 Investigating coral reef ecosystems resilience in the Maldives using benthic foraminfera and corals 01.11.2015 International short research visits
165852 Foraminifera and carbonates as archives of sea level changes: The Maldives and IODP Expedition 359 01.10.2016 Project funding
175587 Unconventional carbonate factories in the Eastern Mediterranean: cold water coral ecosystems and seeps 01.04.2018 Project funding


Tropical and subtropical coral reefs are globally distributed biodiversity hotspots presently threatened by unprecedented forcing. Their ecological functioning and ultimate survival depend on their sensitivity to climatic perturbations and anthropogenic forcing. One of the main visual signs for thermal stress is bleaching, a predominant stressor on reefs, i.e. the loss of the photosynthetic symbionts that lives within their tissues. The increase in magnitude, duration and frequency of coral bleaching events over the last few decades has seriously compromised the resilience of these vulnerable ecosystems. Future bleaching events are predicted to become even more frequent and, therefore, will likely not ensure reef persistence in the Anthropocene. The best approach to gain insights to how global climate change will impact reef ecosystems is to learn from the past. However, in the fossil record, bleaching cannot be observed! The Earth’s paleo-climatic record found in deep sea sediments adjacent to coral reefs can provide us with relevant information on multiple prospective analogues for modern times. In particular, some interglacial periods in the Earth’s history were characterized by climatic conditions similar to modern-day marine environmental conditions, whereas others were warmer. We will investigate deep-sea sedimentary records in basins adjacent to coral reef-bearing carbonate platforms from the Atlantic, Indian and Pacific Oceans in the interval spanning the Present to Marine Isotope Stage (MIS) 31 in the Pleistocene (a time span of around 1100 kyr) and compare with their shallower sediment counterparts. The overarching objective of this research is to evaluate the magnitude and frequency of interglacial periods characterized by anomalously high temperatures that may have produced coral bleaching in the past and to test if nutrients have also contributed to this process. This objective will be achieved by an initial assessment of the modern benthic habitat in the target regions, and the evaluation of photo-inhibition caused by photo-oxidative stress using the large benthic foraminifer Amphistegina (which similarly to corals can undergo bleaching). The modern habitat will be used as a baseline for past evaluation of potential stresses (temperature and nutrients). The resolution of the long-range isotope curves available for the “deep sea” sites will be increased to allow identification of the more negative d18O signals indicating the warmest condition during interglacial MIS. A common age model will be applied to all “deep-sea” sites. ?18O of single specimens of the planktonic foraminifer Globigerinoides ruber (white) and the large benthic Amphistegina will be measured across the thermal maxima of each interglacial MIS in the investigated regions. The parallel use of ?18O composition and the Mg/Ca ratio, as temperature proxies, will help to disentangle which fraction of the d18O signal is due to ice volume and will help to reconstruct more accurate paleo-temperature estimates. The combination of Sr/Ca, Mg/Ca and U/Ca ratios, along with corrected Sr-U and Li/Mg on the coral Porites, accurately dated by U/Th, from the “shallow” sites, will allow us to constrain paleo-temperature for a direct comparison with the “deep” sites. Reactive (bioavailable) phosphorus together with ?13C from the “deep” sites will be used to trace nutrient availability that coupled with anomalously high temperatures may trigger coral beaching. The temperatures obtained from past interglacial extremes will serve to extract the relative frequency and magnitude of temperature extreme events, which went beyond the modern-day bleaching thresholds in order to gain insight into possible scenarios for a warmer world. Novelties of this project are the use of ?18O on single foraminiferal species from the Present down to MIS31 to identify the magnitude and frequency of thermal excess through time and the exploration of chemical elements, whose enrichment or depletion in coral skeletons during bleaching can be used as a potential marker signal in fossil counterparts.This project contributes to the understanding of climate dynamics in tropical and subtropical regions, and to understand the cause of the survival and or decline of coral reefs, which is presently a global serious concern.