Looking for Evidence of Stratospheric Ozone Depletion in Ice at South Pole

University Of Washington, Seattle WA

Investigators

Abstract

The abundance of ozone in the stratosphere is the dominant control on surface ultra-violet radiation, which has important implications for life on Earth. Stratospheric ozone also impacts the Earth's climate system by altering atmospheric circulation patterns, with implications for the ocean carbon cycle and sea ice extent. It has been proposed that the end of the last glacial period, 18,000 years before present, was associated with a period of depleted stratospheric ozone that lasted over 200 years and was caused by a series of large eruptions from the Mt. Takahe volcano in West Antarctica. This ozone depletion may have hastened the end of the last glacial maximum by changing atmospheric circulation patterns, reducing Antarctic sea ice extent and creating increased carbon emissions from the Southern Ocean. This project will test a new method of determining past surface ultra-violet radiation levels by measuring the nitrogen isotopes of nitrate in shallow South Pole ice samples. This research utilizes the modern-day ozone hole over Antarctica to test and calibrate this potential proxy, or substitute, for past Antarctic ozone holes. The nitrogen isotopic composition of nitrate in snow is highly sensitive to the degree of ultraviolet-induced photo-dissociation of that nitrate. This feature makes the measurement of nitrogen isotopes in ice cores a potential proxy (or substitute) for the ozone abundance in the stratosphere, which is the largest determinant of ultraviolet radiation levels at the Earth's surface. A proxy for past surface ultraviolet radiation levels would provide a means to test the hypothesis that a 200-year ozone hole resulting from a series of stratospheric-scale volcanic eruptions in West Antarctica might have triggered rapid Antarctic de-glaciation 18 kyr ago. We propose to test the use of nitrogen isotopes of nitrate as a proxy for past surface-ultraviolet radiation levels by measuring the nitrogen isotopes of nitrate at high resolution in the top 10 m of a previously drilled shallow ice core from the South Pole. The period contained in this ice is 1950-2004 Common Era (C.E.), which will allow researchers to examine and calibrate the nitrate isotope enrichment under the well-known modern-day ozone hole. This will inform the utility of similar measurements on samples from a period of volcanism 18 kyr before present from a new ice core being drilled at the South Pole ice core over the next two years. There is no field work in Antarctica as part of this project.