Publication Date

2020

Document Type

Dissertation/Thesis

First Advisor

Scherer, Reed P.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Earth, Atmosphere and Environment

Abstract

As global climate continues to rapidly change over the coming decades, West Antarctica will continue to be a significant area of concern due to its susceptibility to marine ice sheet collapse. Past collapses during Pleistocene interglacials have been hypothesized but uncertainty exists with respect to the precise timing of specific collapse events. Drill core samples collected from the Amundsen Sea continental rise during IODP Expedition 379 allow for analysis of a more continuous record of Pleistocene glacial-interglacial cycles. Here we report paleotemperature estimates from the Amundsen Sea spanning the last 620 kyr with the objective of identifying likely late Pleistocene WAIS collapses.The paleotemperature estimates are based on the fact that two distinct morphotypes of the dominant Southern Ocean pelagic diatom Fragilariopsis kerguelensis have been shown to reliably reflect summer sea surface temperatures (SST). Using the method pioneered by Kloster et al. (2018) we have analyzed 1,600 diatom specimens in 78 distinct samples down-core in sediment core U1533, establishing a paleotemperature record utilizing the imaging software SHERPA (SHapE Recognition, Processing, and Analysis) which establishes shape (rectangularity) and total valve area of each specimen. The morphotype endmembers include a rounded-tip “High Rectangularity” form, reflecting cold waters, and a pointed tip “Low Rectangularity” form characteristic of warmer waters. Our results show distinct down-core changes in dominant rectangularity, from which we calculate SST, based on a modification of the Glemser and Kloster (2019) equation. We find that the warmest interglacials of the post Mid-Pleistocene Transition period were MIS 15, 13 and 11. Our temperature reconstructions confirm previous suggestions that glacial MIS 14 was characterized by mild interstadial, rather than glacial environmental conditions on the Antarctic margin (Hillenbrand et al. 2009, Konfirst et al. 2012). Collectively, the interval MIS-15 (5.0°C), MIS-14 (4.7°C) and MIS 13 (5.5°C), spanning nearly 100kyr, represents an extended interval of warmth, likely consistent with WAIS retreat. MIS-11 (4.2°C) was likely warm enough to indicate WAIS collapse as well. In contrast, MIS-5e (0.8°C) was not significantly warmer than today, thus not providing strong support for a full WAIS collapse 120 kyr ago. Tracking these changes in SST throughout glacial to interglacial transitions can help constrain ice sheet/ocean models that seek to forecast West Antarctic Ice Sheet behavior in the coming centuries under different warming scenarios.

Extent

51 pages

Language

eng

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

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