Extending Polar Ice Core Records: Studies on the Trapped Air of Glacial Ice from Antarctica, Greenland, and the Canadian Arctic

Abstract

This thesis extends our understanding of ice core records from the polar regions: Antarctica, Summit Greenland, Southern Greenland, and the Canadian Arctic. We date and characterize the geochemical composition of trapped air from ice for these sites.

Beginning in the Antarctic, we present Ar-dating of trapped air from an alpine glacier located in the Dry Valleys, TransAntarctic Mountains. Previous surface-exposure and tephra dating had estimated an age of ~4 Ma for the glacier. We analyze the trapped air and measure an oldest age of 1.6 Ma ±220 ka. The younger gas-age, in addition to geochemical analyses, suggest that the air is a mixture of ancient atmosphere and younger-aged air introduced via cracks in the surface ice. A subtle trend of age with depth suggests that pristine ancient atmosphere may be found deeper within the glacier.

We then move on to the Arctic region, focusing on Summit Greenland. We reconstruct the chronology of the last interglacial (115-128 ka) from the clean, disturbed basal ice of the GISP 2 ice core based on CH4 and δ18Oatm stratigraphy. Using total air content and δ18Oice, we estimate elevation and temperature change. Our data indicate that Summit Greenland elevation decreased by 650 ±200 m during the last interglacial.

At the Southern Greenland site of Dye-3, we again focus on the basal ice. We Ar-date the clean basal ice to 400 ±240 ka, and provide a lower age-limit of 132 ka using gas stratigraphy of the triple isotopic composition of O2 (17Δ). This reconstructed chronology conclusively indicates that Dye-3 was ice covered during the last interglacial, providing important constraints on glaciological models of the Greenland ice sheet.

Finally, we explore basal ice from the Canadian Arctic ice caps: Penny, Devon, and Agassiz. We characterize the basal ice by analyzing its elemental and isotopic composition of O2, N2, and Ar. These data show that the basal ice at all of these sites is a mixture of glacial and superimposed ice. We date the trapped air of the basal ice for the Agassiz 1984 core using 17Δ and δ18Oatm stratigraphy, obtaining a minimum age of 28 ka.