Investigation of Past Atmospheric Methane Variability with Stable Isotopes in Antarctic Ice Cores

Oregon State University, Corvallis OR

Investigators

Abstract

Atmospheric methane contributes to the greenhouse effect and therefore Earth’s temperature. Humans have caused an almost three-fold increase in methane since the industrial revolution. As the planet warms, changes on the Earth surface and in the atmosphere will further change methane levels. How these feedbacks will change over time is not well known. Studies of past variations in methane, by measuring ancient air trapped in ice, provide examples of these changes and help build better predictions of future change. In this project researchers will use measurements of different chemical forms of the carbon and hydrogen in methane to better understand reasons for past changes. The proposed research will develop laboratory measurement methods for hydrogen isotopes, use the different chemical forms of methane to understand the changes in atmospheric methane that happened when past ice ages ended and the Earth warmed, and use unique, very old ice samples (> 1 million years) from Antarctica to understand what controls methane levels in the atmosphere when climate was as warm or warmer than today. Developing new methods involves testing an existing system for purifying methane for measurements of hydrogen isotopes by mass spectrometry. The system is already operational and calibrated for carbon isotopes in methane. Next, the researchers will measure hydrogen isotopes in methane from samples from Taylor Glacier and Allan Hills, Antarctica, that cover two transitions from ice ages to interglacial warm periods. These data will be used to constrain where the methane increase that happened at these times originated, because hydrogen isotope ratios are sensitive to the latitude of the methane source. Finally, the researchers will measure both carbon and hydrogen isotopes in samples from 1 to 3 million years in age from the Allan Hills Blue Ice Area in Antarctica. Comparisons between these measurements and existing data for younger samples may reveal important differences between the mixture of source types that make up the methane budget in these different time periods. For example, prior to 1 million years ago, the apparent lack of large Northern Hemisphere ice sheets during glacial periods, and resulting higher glacial sea levels, would have had impacts on the global wetland methane source. Additionally, warmer temperatures might have increased CH4 emissions from wetlands but also increased production of the hydroxyl radical and methane destruction in the stratosphere. The project will support a post-doctoral researcher who will collaborate with the Ice Drilling Program at Dartmouth College to create virtual field labs used in high school and college classes. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.