Publication Date


Document Type


First Advisor

Dodd, Justin P.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Geology and Environmental Geosciences


Oxygen--Isotopes--Antarctica--Ross Ice Shelf; Silicon--Isotopes--Antarctica--Ross Ice Shelf; Marine sediments--Antarctica--Ross Ice Shelf


Coupled oxygen (δ¹⁸O) and silicon (δ³⁰Si) isotope variations recorded in diatom silica have been increasingly used to reconstruct paleoenvironments and biogeochemical cycling in marine environments. Variations in δ¹⁸O values in diatom silica are used to reconstruct oceanographic conditions such as water temperature and water mass mixing. Corresponding δ³⁰Si variation in diatom silica record silicic acid utilization by diatoms, which is related to changes in primary productivity, global silicon cycling, and carbon cycle dynamics. Diatom silica is a particularly significant paleoenvironmental proxy in high-latitude environments, such as the Southern Ocean, where diatom blooms are abundant and there is a lack of carbonate microfossils (i.e. foraminifera). An ideal location to employ δ¹⁸O and δ³⁰Si as a paleoceanographic proxy is in a -80-m long Pliocene diatomite unit of the AND-1B marine sediment core collected from beneath the Ross Ice Shelf in McMurdo Sound, Antarctica. The results of this study demonstrate that δ¹⁸O values in diatom silica record early diagenetic conditions and variations in pore water δ¹⁸O values. Calculated δ¹⁸O values of AND-1B sediment pore water values are between -16 and -8‰, which is consistent with the δ¹⁸O values of cryogenically formed brines associated with pore waters in the nearby AND-2A sediment core. Changes in the δ¹⁸O value of the diatom silica/pore water through time likely reflect variability in subsurface brine input into McMurdo Sound during the Pliocene. The diatom silica δ³⁰Si values appear to be well correlated with variations in the LR04 benthic stack δ¹⁸O values as well as reconstructed surface water temperatures based on diatom assemblages in the same interval of AND-1B. The correlation between the δ³⁰Si values and other global proxies suggest the δ³⁰Si values are less susceptible to diagenesis, and the large variations in δ³⁰Si values of ~1.6‰ are most likely the result of significant changes diatom productivity and surface water nutrient utilization. Combined, the δ¹⁸O and δ³⁰Si values in the diatom silica indicate that there were significant variations in the paleoenvironment, diatom productivity, and cryogenic brine formation in the Ross Sea during the Pliocene.


Advisors: Justin P. Dodd.||Committee members: Mark Frank; Ross Powell.||Includes bibliographical references.||Includes illustrations and maps.


vii, 79 pages




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