Date of Award

8-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

College/School

College of Science and Mathematics

Department/Program

Earth and Environmental Studies

Thesis Sponsor/Dissertation Chair/Project Chair

Stefanie A. Brachfeld

Committee Member

Sandra Passchier

Committee Member

Matthew L. Gorring

Abstract

Barilari Bay is located on the western side of the Antarctic Peninsula (AP), opposite the former Larsen B Ice Shelf on the eastern Antarctic Peninsula. Barilari Bay was swath mapped during United States Antarctic Program cruise NBP10-01 as part of the Larsen Ice Shelf System, Antarctic (LARISSA) program. The bay consists of a series of five basins with water depths greater than 600 meters, from which a suite of kasten cores and jumbo piston cores was collected. Three cores, JPC-127, its trigger core TC- 127, and JKC 55 were collected from the outer portion of the Bay and recovered an 8.5-m thick sequence of glacial-marine sediment. The low-field magnetic susceptibility (xif) profile of JPC-127 indicates relatively higher xif and low amplitude variability at the top of the core from 250 cm to 420 cm. The bottom portion of the core, from 425 cm to 850 cm, shows high amplitude variability with a 50-100 cm wavelength. The xif profile for TC-127 indicates relatively higher xif and low amplitude variability from 0 cm to 115 cm. Radiocarbon dates are not yet available; however, comparison of the JKC-55 xif profile with the JPC-127 xif profile suggests that 80 cm is missing from the top of JPC-127. The shape of the susceptibility profile from top to bottom may result from more recent and persistent sea ice cover, preceded by an earlier period with fluctuating biological productivity. The base of the outer Barilari Bay profile resembles the late Holocene segment of susceptibility profiles from regions to the north, such as the Palmer Deep and Andvord Bay. Magnetic hysteresis measurements indicate coarser grained magnetic material in the lower part of the core, possibly a combination of increased ice rafting and post-depositional dissolution of fine-grained magnetite. S-ratios for each sample were used as a rapid reconnaissance parameter for mineralogy. All upper core samples have values that are consistent with the presence of magnetite. This is also the case for susceptibility peaks from the lower part of the core. In the lower part of the core, S-ratios from susceptibility lows suggest the presence of a high-coercivity mineral such as hematite or goethite in addition to magnetite. Thermomagnetic measurements indicate that magnetic Fe-sulfides are present throughout the core; therefore, diagenesis is not limited to the bottom part of the recovered section. Sub-micron magnetite grains are observed in lithic fragments from an inner bay core, JPC-125, which may be the source of the fine-grained magnetite that dissolved in the lower part of the core. Hematite is observed in the thermomagnetic curves throughout the core, further indicating that higher-coercivity minerals are not unique to the bottom of the section. Total carbon increases down core, which may indicate that enough organic C was available to allow diagenetic reactions to go to completion. Al/Ti values range from 21.6 to 27.2, indicating an upper continental crust provenance. The Fe/Ti profile exhibits an inverse relationship with the Al/Ti profile but a direct relationship with the xif profile. Superparamagnetic magnetite may be influencing the xjf profile while not substantially influencing the geochemistry. Available diatom data suggests that the base of JPC-127 may have recovered the middle Holocene. When chronology is available, more definitive comparisons can be made with other locations on the AP.

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