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Dissertation/Thesis Abstract

An organic geochemical perspective on tropical East African paleoclimate
by Tierney, Jessica E., Ph.D., Brown University, 2010, 253; 3430215
Abstract (Summary)

Recent development of biomarker-based paleoclimate proxies provides new analytical capabilities through which paleoenvironmental change can be inferred. Here, I explore the utility of these organic proxies towards solving problems of tropical paleoclimatology within East Africa. Specifically, I apply compound-specific deuterium/hydrogen (D/H) ratios, compound-specific carbon isotopic ratios, and tetraether-based paleoproxies to lake sediments from East Africa (Lake Tanganyika and Lake Challa) to test the ability of these novel proxies to infer past changes in the hydrological cycle, terrestrial vegetation, and surface temperature. I demonstrate that compound-specific D/H ratios, as measured on terrestrial higher plant leaf waxes, are a robust, albeit complex proxy for past changes in East African hydrology over a variety of timescales (multidecadal-orbital). The use of glycerol dialkyl glycerol tetraethers (GDGTs) as paleothermometers in lacustrine environments is also explored in depth. I show that the Tetraether Index of 86 Carbons (TEX86) proxy is a reliable proxy for lake surface temperature in Lake Tanganyika over both short (last two millennia) and long (60,000 years) timescales. However, TEX86 is not universally applicable in lacustrine systems. With this in mind, I demonstrate in a surface transect study that branched GDGTs, ubiquitous compounds in terrestrial soils, are also abundant in East African lake sediments, and show considerable promise as an alternative lacustrine paleothermometer.

In summary, I demonstrate that organic geochemical techniques provide powerful new insights on East African paleoclimate, including orbital controls on climate, and the influence of remote, high-latitude teleconnections. Furthermore, D/H ratios inferred from leaf waxes and tetraether-inferred changes in temperature provide quantitative paleodata suitable for proxy-model comparison.

Indexing (document details)
Advisor: Russell, James
School: Brown University
School Location: United States -- Rhode Island
Source: DAI-B 71/11, Dissertation Abstracts International
Subjects: Geology, Paleoclimate Science, Geochemistry
Keywords: Deuterium/hydrogen ratios, Hydrological cycle, Paleoclimate, Surface temperature, Terrestrial vegetation, Tropical climate
Publication Number: 3430215
ISBN: 978-1-124-30148-8
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