Date of Award

8-2009

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

Stefani A. Brachfeld

Committee Member

Sandra Passchier

Committee Member

Michael Kruge

Abstract

A 24-m jumbo-piston core containing a 14 ka Holocene-Late Pleistocene sedimentary record was collected from Mac.Robertson Land during United States Antarctic Program cruise NBP01-01. This study uses environmental magnetism to trace the Holocene history of the East Antarctic Ice Sheet (EAIS), which is generally thought of as stable since it is grounded above sea level. Magnetic analyses are used to identify periods of terrigenous sedimentation from the EAIS, for example ice rafted debris layers or meltwater pulses. Terrigenous material contains magnetic minerals, which we expect to stand out from the dominantly biosiliceous sediment deposited along the East Antarctic Margin. Magnetic susceptibility is weak down core (approximately -2 to 5 *10-8 m3/kg) until approximately 10.0 ka where there is a steep increase in intensity, most likely due to sandy mud laminae and underlying diamict. Analysis of X-rays down core show periods of high and low frequency of laminations down core, until a varved layer stratigraphically above the diamict (5-16 laminations per 5 cm). Gravel grains are sparsely present down core until the diamict, where they are ubiquitous. These changes in lithology represent déglaciation following the last glacial maximum and the transition to an open marine environment at 14 ka. Based on ARM and SIRM data, the upper core (0.8-7.7 ka) exhibits a low abundance of magnetic material until approximately 7.7 ka, where there is an increase in fine magnetic material above the background until 10.4 ka. Magnetic assemblages for the upper core (approximately 0.8-9.0 ka) likely consist of magnetite and titanomagnetite based upon SIRM/X and S-ratio values of 0.1 - 12 kA/m and 0.9- 0.95, respectively (Evans and Heller, 1999). The assemblage changes in the lower core (prior to 9.0 ka) with isolated peaks in SIRM/X suggesting magnetic iron sulfites (greigite and pyrrhotite) and also the presence of high coercivity minerals such as hematite and goethite. From 0.8 to 4.4 ka, ARM exhibits a zone of regularly spaced peaks occurring on a ~ 300-700 year scale, which is a cycle typically seen in the Antarctic Peninsula during the late Holocene (e.g., Domack et al., 2001 and references therein) and interpreted as a productivity signal. A magnetic-rich interval above the background ARM and SIRM levels is seen between 7.7-10.4 ka. This period partially coincides with an early Holocene warm period seen on the Antarctic Peninsula (Leventer et al. 2002). The magnetic enrichment could have been caused by increased terrigenous input through meltwater as the nearby ice sheet retreated. This has been observed on the Antarctic Peninsula and possibly other locations such as the Canadian Arctic, Chukchi-Alaskan margin, and other western Antarctic regions (Brachfeld et al., 2009; Leventer et al., 2002; Roberts et al., 2004; Vare et al., 2009). This promotes the idea that the Holocene Thermal Maximum is likely a global occurrence, rather than a local event.

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