Insights about the climate, atmosphere, and ice sheets of the past from analysis of nitrogen, oxygen, and argon gas in Antarctic ice cores

Studying past climate change offers a valuable way of observing how the climate system responds to natural forcings. Ice cores from the polar regions are an excellent tool for investigating past climate, in part thanks to the unique archive of atmospheric air preserved in the glacial ice. The most abundant components of this air are, of course, nitrogen, oxygen, and argon, each of which records valuable information about past climate. This thesis explores the climate of the Last Glacial Period using measurements of the isotopic composition of nitrogen, oxygen, and argon in ice core air.Chapter 2 discusses fluctuations in the properties of the snow and firn at the South Pole during the past 30,000 years. The largest fluctuations are the result of past changes in katabatic wind speed linked to variations in surface topography upstream of the ice core site. In addition, the data, together with a series of modelling experiments, provide evidence that the ice core data are affected by a seasonal bias. The bias is also linked to past wind speed and topography at the ice core site and has the potential to impact other, similar ice core records. Chapter 3 utilizes ice core records of the isotopic composition of atmospheric oxygen to investigate the response of tropical hydroclimate and the terrestrial biosphere to abrupt climate change during the Last Glacial Period (Dansgaard-Oeschger and Heinrich Events). The data show that tropical precipitation and global photosynthetic oxygen production migrate northward and southward in response to abrupt warming and cooling in the North Atlantic, taking approximately 1,000 years to adjust to the new climate state. Chapter 4 presents an improved analytical method for making precise measurements of the isotopic and elemental ratios of nitrogen, oxygen, and argon in whole-air (i.e., without splitting or purifying the ice core air sample). The results are (i) a method capable of measuring the three gases with a precision suitable for detecting ice core signals, and (ii) recommendations for further development and application of the method to ice core samples. In sum, the findings presented here advance our understanding of how wind-speed and topography affect ice core gas records, how tropical hydroclimate and the terrestrial biosphere respond to abrupt climate change, and how to better make precise measurements of these gases in ice core samples