This thesis uses the paleoceancirculation proxy <sup>231</sup>Pa/<sup>230</sup>Th, coupled with water mass tracers δ<sup>13</sup>C and εNd, to reconstruct circulation histories for southern source waters masses in the South Atlantic, in addition to North Atlantic Deep Water (NADW) far from its source, for the last ~25 kyrs. Downcore <sup>231</sup>Pa/<sup>230</sup>Th records from a suite of cores along a depth transect in the Argentine Basin show distinct differences with depth, suggesting that <sup>231</sup>Pa/<sup>230</sup>Th ratios in sediments are reflective of conditions in only the bottom most waters. This indicates the importance of consideration of changes in water mass distribution when interpreting <sup>231</sup>Pa/<sup>230</sup>Th records. Opal and particle flux data from these cores show little correlation with <sup>231</sup>Pa/<sup>230</sup>Th values meaning that changes in <sup>231</sup>Pa/<sup>230</sup>Th cannot be explained by a local composition or particle flux effect and are instead likely to be reflecting changes in circulation. A core bathed by Antarctic Intermediate Water (AAIW) throughout the last 25 kyrs (GeoB 2107, 1045 m), has relatively high <sup>231</sup>Pa/<sup>230</sup>Th values (0.075) during the Holocene and distincly lower values (0.055) at the LGM suggesting faster AAIW transport during the last glacial. At greater depths, <sup>231</sup>Pa/<sup>230</sup>Th, δ<sup>13</sup>C and εNd data in core GeoB 2109 (2504 m) indicate a change in both circulation and water mass distribution on glacial-interglacial timescales, with moderate flow of Antarctic Bottom Water (AABW) at the LGM being replaced by more vigorous flow of NADW during the Holocene. On millenial timescales, <sup>231</sup>Pa/<sup>230</sup>Th values in deep cores GeoB 2109 and GeoB 2112 (4010 m) indicate enhanced production of AABW during northern hemisphere stadials, when variations in <sup>231</sup>Pa/<sup>230</sup>Th records are of opposite sign between hemispheres, supporting a possible bipolar seesaw relationship in deep water formation between hemispheres. These data indicate that the <sup>231</sup>Pa/<sup>230</sup>Th proxy can be used to reconstruct past flow rates of multiple water masses in the Argentine Basin and provide evidence that southern source water masses play a dynamic counterpart to NADW formation on abrupt as well as glacial-interglacial timescales.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:580864 |
| Date | January 2010 |
| Creators | Hickey, Benjamin J. |
| Contributors | Henderson, Gideon M.; Thomas, Alexander |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:ee1b4b21-ffd7-4356-bbfd-4af94f01c291 |
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