Noble Gases in Ice Cores: Indicators of the Earth’s Climate History

Abstract

Polar ice cores constitute excellent archives of past environmental conditions and provide us with glimpses into the Earth’s climatic history over hundreds of thousands of years. For the past two decades, noble gases, used as conservative tracers, have played a substantial role in extracting information from these archives. Noble gas analysis can be performed on two types of ice core samples. First, atmospheric air, trapped in bubbles in polar ice, can be extracted and analyzed for its noble gas composition. Variations in the isotopic and elemental composition of noble gases reveal changes in the composition of the paleoatmosphere or the impact of climate-related physical processes acting when the air was enclosed. For example, thermal fractionation allows for the creation of a ‘gas isotope thermometer’ in ice cores. Second, particles that were deposited on the surface snow and incorporated in the ice matrix can be analyzed for their noble gas isotope composition. These analyses reveal information about the input and origin of both terrestrial aerosols and extraterrestrial dust. The conservative nature of noble gases, ensuring that such fingerprints will be preserved over long periods of time, and the exceptionally good dating of polar ice cores make noble gas analysis of ice cores a versatile tool to study a wide spectrum of geochemical and paleoclimatic processes: from constraints on the magnitude of temperature changes during abrupt climate transitions in the Earth’s history, to determining the rate of Argon-40 degassing from the solid Earth over its history, or quantifying variations in the accretion of extraterrestrial dust on the Earth’s surface. Below, we present case studies to review some of the applications of noble gas analysis in the polar ice archive, both in trapped air bubbles and in particles incorporated in the ice matrix.