| Summary: | The study of past ocean processes is essential to the understanding of current oceanography and climate systems, and to the prediction of future global change. The study of paleoceanography requires proxies: to date many studies have used foraminifera and reef corals. Each of these tools, however, has its limitations. The time resolution of paleoceanographic reconstruction using forams can be very poor, while reef corals can only give information about shallow, tropical processes. Azooxanthellate corals, in contrast, are suitable for highly precise and accurate radiogenic dating and are found everywhere in the world oceans, at all depths. The few attempts to use this taxon for paleoceanographic work have been, for the most part, unsuccessful. This is because the techniques for decoding the environmental information stored within azooxanthellate skeleton had not yet been developed. This thesis represents the first attempt to extract paleoceanographic information from 'deep-sea' corals and is presented in five sections, each a published for publishable manuscript. Part 1 describes an investigation of corals from Orphan Knoll (Desmophyllum cristagalli from 1600 m depth), in the northwest Atlantic. They were dated by the ²³⁰Th/²³⁴U method using thermal ionization mass spectrometry (TIMS) and found to have grown around the time of the Younger Dryas cooling event (13,000 to 11,700 calendar years BP). The origin of this cooling recently been attributed to a reduction or cessation of deep-water producution in the North Atlantic and a concurrent lessening of the heat flux from low latitudes. The δ¹⁸O in the coral skeletons shift markedly, coincident with the initiation of the Younger Dryas, suggesting that profound changes in intermediate water circulation may have occurred. Part 2 describes a study of skeletogenesis in deep-sea corals in order to develop a suitable isotopic sampling scheme for 'time-series' analyses. Numerous scanning electron micrographs of D. cristagalli have shown that this organism has skeletal ...
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