Date of Award

8-2014

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Brenda L. Hall

Second Committee Member

George H. Denton

Third Committee Member

Karl J. Kreutz

Abstract

The marine-based West Antarctic Ice Sheet (WAIS) has been hypothesized to be inherently unstable (Mercer, 1978), and if it were to melt, would contribute between 3 to 5 m of global eustatic sea-level rise (Bamber et al., 2009). With the recent collapse of the Larsen B ice shelf attributed to continuous Holocene thinning, amplified by recent warming (Domack et al., 2005), the future stability of other ice shelves remains a critical question. In particular, predicting the future stability of the Ross Ice Shelf (RIS) is essential because of its role in buttressing ice from the WAIS. One way to assess the sensitivity of the RIS, and hence the WAIS, to rising temperatures is to determine ice- shelf behavior during past periods of warmer-than-present temperatures.

The aim of this project was to develop a record of Holocene seawater temperatures for the McMurdo Sound region of Antarctica and to use these data to address questions of Holocene climate change and RIS sensitivity to ocean temperature change. I reconstructed paleotemperatures from 6500 years ago to present from the oxygen-isotope ratios of sub-fossil Adamussium colbecki (A. colbecki), marine bivalve mollusks. The equation of Kim and O’Neil (1997) afforded the best approximation of the δ18O-temperature relationship for adult A. colbecki. In addition, Mg/Ca ratios were measured in order to obtain an independent relative-temperature record to compare with δ18O-reconstructed temperatures.

Results show that shells dating to 6500-2000 years before present (yr BP) yield warmer-than-present temperatures (by ~0.8 °C). By 1000 yr BP, seawater temperatures had begun to cool in McMurdo Sound. The coldest temperatures for the past 6500 years are recorded by modem A. colbecki. This pattern of Holocene climate change is consistent with existing data from marine animals, glaciers, and ice shelves along the Victoria Land Coast, that suggest a relatively warm mid-Holocene with cooling in the last millennium.

The data from this study bear on the behavior of the RIS and the smaller adjacent McMurdo Ice Shelf over the Holocene. The moderately warmer ocean temperatures in the mid-Holocene were not sufficient to cause the RIS to retreat from its pinning point at Ross Island and Minna Bluff. Thus, the RIS may be tolerant to modest amounts of future warming that are in the range of mid-Holocene values. However, the thinner McMurdo Ice Shelf is thought to have retreated over the last 6000 years, possibly as a result of the relatively warm ocean temperatures. If true, then one possibility is that future warming will lead to further recession and eventual loss of the McMurdo Ice Shelf. Such loss might impact the adjacent RIS and cause it to lose contact with the pinning points that currently prevent it from recession into the inner Ross Embayment.

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