The trace element content of calcareous foraminifera provides a powerful tool to the study of glacial-interglacial changes in the physical and chemical properties of the ocean. Foraminifera incorporate barium in direct proportion to its concentration in seawater. Using barium as a nutrient proxy, Ba/Ca in benthic <i>Planulina wuellerstorfi</i> is used to reconstruct changes in thermocline ventilation and mid-depth circulation in the North Atlantic during the last glacial and deglacial time. Rivers are concentrated in barium compared to surface seawater. Therefore, barium in planktonic <i>Neogloboquadrina pachyderma</i> is used to identify deglacial meltwater in the Arctic Ocean. Foraminiferal Li/Ca was analyzed to elucidate factors influencing incorporation behavior, including interspecies differences, temperature, pressure, dissolution, and shell mass. To investigate the use of lithium isotopes as a proxy for paleo-seawater chemistry, <font face="symbol">d</font><sup><small>6</small></sup>Li was determined in planktonic <i>Orbulina universa</i>.
During the last glacial maximum, nutrients in the thermocline and the intermediate water of the North Atlantic was lower than today due to increased ventilation and the presence of nutrient-depleted Glacial North Atlantic Intermediate Water (GNAIW). During deglacial time, GNAIW was replaced by southern component water, resulting in an enrichment of nutrients in the mid-depth Atlantic water. Increased Ba/Ca in the surface Arctic Ocean indicates an increase in meltwater discharge between 12.4 and 11.3 <sup><small>14</small></sup>C ka BP. This may have triggered an increase in the export of freshwater to the North Atlantic, contributing to a shutdown in GNAIW production, and leading to the onset of the Younger Dryas. A second meltwater event at 9.4 <sup><small>14</small></sup>C ka BP may be the result of glacial Lake Agassiz draining through the Clearwater spillway to the Mackenzie River. Foraminiferal Li/Ca shows systematic glacial-interglacial variation coincident with <font face="symbol">d</font><sup><small>18</small></sup>O. The incorporation behavior of lithium in foraminifera does not appear to be dominated by changes in temperature, pressure, dissolution, or shell mass, but is potentially controlled by changes in growth conditions, including calcification rate. Preliminary work indicates that <font face="symbol">d</font><sup><small>6</small></sup>Li remained constant throughout the Holocene and the last glacial maximum at 30.5 ± 1.1. Further developmental studies are necessary to fully engage lithium isotopes as a tracer of seawater composition.
| Identifer | oai:union.ndltd.org:LSU/oai:etd.lsu.edu:etd-0710102-192931 |
| Date | 11 July 2002 |
| Creators | Hall, Jenney M |
| Contributors | John Wrenn, Ajoy Baksi, Lui-Heung Chan, Phil Bart, Laurie Anderson, Jeff Hanor, Robert Rohli |
| Publisher | LSU |
| Source Sets | Louisiana State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lsu.edu/docs/available/etd-0710102-192931/ |
| Rights | unrestricted, I hereby grant to LSU or its agents the right to archive and to make available my thesis or dissertation in whole or in part in the University Libraries in all forms of media, now or hereafter known. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. |
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