| Summary: | The last deglacial period, spanning 21,000 to 10,000 years before present, has been studied extensively to quantify Earth system responses to changes in climate forcings like greenhouse gas concentrations. During this time, the Earth system underwent near-synchronous changes: atmospheric greenhouse gas concentrations and surface temperatures increased, ice volume and sea ice extent decreased resulting in sea level rise while atmospheric and ocean circulation patterns underwent drastic changes. Paleoclimate archives are used extensively to understand the causes and quantify the magnitude of these past changes. However, most of these studies are focused on the surface. Little information exists about the vertical profile of the atmosphere, namely how high-altitude temperatures and stratosphere-to-troposphere transport fluxes evolve with a rapidly evolving climate. Understanding the evolution of the vertical thermal structure of the atmosphere is necessary for quantifying how temperature lapse rates change with changing climate. Furthermore, air mass exchange between the stratosphere and the troposphere governs the chemistry of both regions and is expected to accelerate in a warming world. Thus, evaluating how high-altitude temperatures and atmosphere circulation evolved in the past is crucial for predicting their changes in the future. This dissertation evaluates the potential for a novel ice core proxy record, clumped isotopic composition of molecular oxygen measured in occluded air in polar ice cores, to provide constraints on how high-altitude temperatures and stratosphere-to-troposphere transport evolved during the last deglacial period. Clumped isotopic composition of oxygen, denoted by Δ36, is the proportional abundance of two heavy isotopes of oxygen, i.e., 18O18O in O2 and its formation is sensitive to the thermal and photochemical properties of the atmosphere. Isotope exchange reactions in the stratosphere and troposphere and mass exchange between the two governs the net surface Δ36 value. Evaluation of ...
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