New approaches to coccolith geochemistry and its application to Cenozoic paleoceanography
The use of coccolithophores has until recently been restricted mainly to biostratigraphic indicators. Their small size makes it difficult to obtain species-specific geochemical data and they are often perceived to preserve poorly compared with the larger foraminifer. In the last decade the study of...
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| Other Authors: | , , |
| Format: | Doctoral or Postdoctoral Thesis |
| Language: | unknown |
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Imperial College London
2015
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| Online Access: | http://hdl.handle.net/10044/1/53385 https://doi.org/10.25560/53385 |
| Summary: | The use of coccolithophores has until recently been restricted mainly to biostratigraphic indicators. Their small size makes it difficult to obtain species-specific geochemical data and they are often perceived to preserve poorly compared with the larger foraminifer. In the last decade the study of potential coccolithophore bio-geochemical proxies has taken off, but with little to support their use in deep-time records. The suitability of fossil coccolithophores for geochemical proxies has been examined. A large collection of trace metal data from individual coccoliths throughout the Cenozoic has been collected, from a range of taxa. Using SIMS it has been demonstrated that the Sr/Ca values from fossil coccoliths are comparable to those collected from their modern counterparts. It has also been possible to examine the distribution of ions within individual coccoliths, revealing that their original calcite is preserved and the effects of diagenesis can often be overcome. For the first time a high-resolution record of Sr/Ca from calcareous nannofossils has been produced over the Eocene/Oligocene transition, (~34 to 33.5 Ma). This period of extreme climate change resulted in the permanent formation of ice, for the first time in the Cenozoic, at the Antarctic within ~400 ky, accompanied by a general shift to a modern climate state. This shift is associated with changes in nutrient cycling and/or ocean thermal structure due to changes in ocean circulation. It is still debated about how these changes affected productivity in the equatorial Pacific at this time. The Sr/Ca proxy provides a direct record of coccolithophore productivity. Using samples from IODP Site U1334, bulk and individual coccolithophore carbonate are examined, in combination with the coccolithophore isotopic record. The factors affecting the records are examined in detail and reveal a significant shift in productivity over the E/OT, associated with isotopic changes. Open Access |
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