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Atmospheric Noble Gases As Geochemical Tracers In The Earth System


Measurements of noble gas in the atmosphere are a powerful tool to study natural and anthropogenic changes in the Earth system. The chemically inert nature of noble gases means that they are only impacted by physical processes, greatly simplifying the interpretation of observations. Furthermore, fast atmospheric mixing intrinsically integrates global signals on time scales beyond one year allowing local records to capture global changes. Air samples can be obtained in a variety of ways including directly from the atmosphere, from reservoirs intentionally archived by humans, or from small bubbles trapped naturally in ancient ice, enabling the reconstruction of atmospheric changes over a wide range of timescales. However, atmospheric noble gas measurements are challenging because the signals we chase are often small, and analytical methods are still being developed and improved upon.

In four chapters, this dissertation aims to deepen our understanding of noble gases as geochemical tracers and highlights new methods and applications of noble gas analyses. Chapter 1 explores the processes that cause small offsets between atmospheric air and air preserved in ice using a 2-D numerical model of air transport through snow. Chapter 2 demonstrates a connection between atmospheric circulation in the upper atmosphere and the in-situ argon-to-nitrogen (Ar/N2) ratio using samples collected by aircraft. Chapter 3 introduces a novel mass spectrometric technique for the precise measurement of small changes in the atmospheric helium abundance and outlines potential scientific applications. Finally, Chapter 4 builds on Chapter 3 and presents the first record of an atmospheric helium build-up which can be linked directly to anthropogenic fossil fuel activity.

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