High-Resolution Water Isotope Records from West Antarctic Ice Cores: Interpretations of Climatic, Glaciological, and Diffusional Processes

Jones, Tyler Robert

Graduate Thesis Or Dissertation

High-Resolution Water Isotope Records from West Antarctic Ice Cores: Interpretations of Climatic, Glaciological, and Diffusional Processes Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/2227mp66q

Abstract

To place current climate change in context, it is necessary to study geologic proxy records that extend beyond historical documentation. One such proxy is polar ice cores, which contain climatic information many thousands of years into the past. In East Antarctica, a ~700,000 year ice core record shows that Earth climate has shifted between glacial (cold) and inter-glacial (warm) conditions seven times, mirrored by atmospheric CO2 concentrations. In Greenland, ~100,000 year ice core records show that climate has changed abruptly within years to decades. These long-term and short-term changes frame our understanding of the climate system, and allow for informed predictions about future climate change. In this dissertation, we study a number of ice core records from West Antarctica. We first present a series of seven shallow ice cores from Siple Dome, West Antarctica. The shallow cores are used to investigate high-frequency variability in water isotopes (a proxy for local temperature and regional atmospheric circulation). Although the shallow cores span only 60 km, a microclimate effect causes distinct differences across the dome - an effect that should be considered in the interpretations of longer ice cores taken from coastal West Antarctic locations. We then shift focus to the analysis of an ultra-high resolution water isotope record from the inland West Antarctic Ice Sheet (WAIS) Divide ice core (WDC). This record was analyzed using laser absorption spectroscopy, consists of over 24 million data points, and extends to 68,000 years before present. It is the highest-resolution and longest continuous ice core climate record ever recovered from Antarctica. A number of analyses are performed, including: 1) Quantification of diffusional processes, 2) Reconstruction of high-frequency decadal and sub-decadal oscillations, and 3) Analysis of low-frequency millennial-scale oscillations. The results of the WDC water isotope study hold important insight into Antarctic climate patterns. The annual signal is found to trend with solar insolation over the last 10 thousand years. The strength of 2 to 15-year variability - which may originate as part of the El Niño Southern Oscillation (ENSO) in the tropical Pacific Ocean - exhibits distinct differences between the most recent glacial and interglacial periods. At the millennial-scale, variability appears to be partially driven by solar activity. A regular oscillation (of solar origin or otherwise) is evident in the water isotope record for the last 68 thousand years, and may hold clues to the initiation of abrupt climate change events documented in Greenland ice cores. Ultimately, the resolution of the WDC record allows for the assessment of climate change on the order of a presidential term (4 years) or less over most of the last glacial-interglacial cycle. More importantly, the results provide context for current and future anthropogenic climate change by defining natural variability in the past.

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