Coral biomineralization, climate proxies and the sensitivity of coral reefs to CO2-driven climate change DeCarlo, Thomas M. 2016-11-23T14:36:41Z 2016-11-23T14:36:41Z 2017-02
dc.description Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2017 en_US
dc.description.abstract Scleractinian corals extract calcium (Ca2+) and carbonate (CO2−3) ions from seawater to construct their calcium carbonate (CaCO3) skeletons. Key to the coral biomineralization process is the active elevation of the CO2−3 concentration of the calcifying fluid to achieve rapid nucleation and growth of CaCO3 crystals. Coral skeletons contain valuable records of past climate variability and contribute to the formation of coral reefs. However, limitations in our understanding of coral biomineralization hinder the accuracy of (1) coral-based reconstructions of past climate, and (2) predictions of coral reef futures as anthropogenic CO2 emissions drive declines in seawater CO2−3 concentration. In this thesis, I investigate the mechanism of coral biomineralization and evaluate the sensitivity of coral reef CaCO3 production to seawater carbonate chemistry. First, I conducted abiogenic CaCO3 precipitation experiments that identified the U/Ca ratio as a proxy for fluid CO2−3 concentration. Based on these experimental results, I developed a quantitative coral biomineralization model that predicts temperature can be reconstructed from coral skeletons by combining Sr/Ca - which is sensitive to both temperature and CO2−3 - with U/Ca into a new proxy called “Sr-U”. I tested this prediction with 14 corals from the Pacific Ocean and the Red Sea spanning mean annual temperatures of 25.7-30.1°C and found that Sr-U has uncertainty of only 0.5°C, twice as accurate as conventional coral-based thermometers. Second, I investigated the processes that differentiate reef-water and open-ocean carbonate chemistry, and the sensitivity of ecosystem-scale calcification to these changes. On Dongsha Atoll in the northern South China Sea, metabolic activity of resident organisms elevates reef-water CO2−3 twice as high as the surrounding open ocean, driving rates of ecosystem calcification higher than any other coral reef studied to date. When high temperatures stressed the resident coral community, metabolic activity slowed, with dramatic effects on reef-water chemistry and ecosystem calcification. Overall, my thesis highlights how the modulation of CO2−3, by benthic communities on the reef and individual coral polyps in the colony, controls the sensitivity of coral reefs to future ocean acidification and influences the climate records contained in the skeleton. en_US
dc.description.sponsorship This research was funded by a National Science Foundation (NSF) Graduate Research Fellowship, NSF grants OCE 1041106, OCE 1338320, and OCE 1220529, by a thematic project at Academia Sinica, Taiwan, the WHOI Ocean Ventures Fund, and by the WHOI Coastal Ocean Institute. en_US
dc.identifier.citation DeCarlo, T. M. (2017). Coral biomineralization, climate proxies and the sensitivity of coral reefs to CO2-driven climate change [Doctoral thesis, Massachusetts Institute of Technology and Woods Hole Oceanographic Institution]. Woods Hole Open Access Server.
dc.identifier.doi 10.1575/1912/8550
dc.language.iso en_US en_US
dc.publisher Massachusetts Institute of Technology and Woods Hole Oceanographic Institution en_US
dc.relation.ispartofseries WHOI Theses en_US
dc.subject Corals
dc.subject Coral reef ecology
dc.title Coral biomineralization, climate proxies and the sensitivity of coral reefs to CO2-driven climate change en_US
dc.type Thesis en_US
dspace.entity.type Publication
relation.isAuthorOfPublication 8e0c3ecf-cf2d-4355-a41d-d55674ae6b6f
relation.isAuthorOfPublication.latestForDiscovery 8e0c3ecf-cf2d-4355-a41d-d55674ae6b6f
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