Laura Vogel

2009 JISAO/NCAS Research Internship

Analyzing ice core samples from the Atlantic

Laura VogelThis summer I have been privileged to be a JISAO intern working at the University of Washington in the Department of Atmospheric Sciences. This fall I will be entering my junior year as an undergraduate at Columbia University, pursuing a degree in Environmental Science. I wanted to get real research experience this summer to see what it is like, to learn more about an aspect of the environment, and with this internship specifically to help our understanding of the atmosphere. Climate change, closely related to this area of research, has been an interest of mine for some time but before this summer I had only been able to contribute by doing things like turning off the lights and driving a hybrid car.

My mentor, Professor Becky Alexander, works to understand variations in the chemical composition of the atmosphere. The research I am a part of is a large collaborative project called the WAIS (Western Antarctic Ice Sheet) Divide Project, which revolves around the WAIS Divide core, a high-resolution long ice core. There are around twenty related projects surrounding the core, and the overall goal is to develop climate records from the information gathered from the ice. This includes the first complete record of multiple isotope ratios of nitrate and sulfate over the past 100,000 years. Professor Alexander is measuring the oxygen and nitrogen isotopes in nitrate collected from the ice, and I am helping her with roughly 400 meters of measurements. We are also sending samples of melted ice to UCSD for sulfate measurements.

Measuring the isotopes of nitrate in the ice provides two pieces of information; the oxygen isotopes will tell us about how the nitrate was produced in the atmosphere, while the nitrogen isotopes will provide information on sources of nitrate. Understanding nitrate production is important for a better understanding of oxidation pathways of the atmosphere. The oxidative capacity of the atmosphere ice core samplecontrols atmospheric chemistry, and it is typically defined by OH radical concentrations. It determines the lifetime of important

trace species such as methane and carbon monoxide. The oxygen isotopes of nitrate and sulfate provide a proxy for past OH concentrations because the "mass-independent" fractionation (D17O) signature of ozone is preserved in nitrate and sulfate from the interaction of their precursors with ozone, whereas interaction with OH produces a "mass-dependent" isotope fractionation signature. Therefore, D17O values in nitrate and sulfate are an indicator of the role of ozone (mass-independent) versus OH (mass-dependent) oxidation.

I worked mostly with the ice itself (see video below), hauling boxes of meter-long samples out of the big freezers and melting them. My job was to extract the nitrate from the samples so I passed the melted ice through columns packed with an anionic resin, which retains nitrate. I gave these concentrated samples of nitrate to the Isotope Lab: there the nitrate was converted to nitrous oxide using denitrifying bacteria and then the isotopes were measured on an Isotope Ratio Mass Spectrometer. I was able to experience the IsoLab in action as well, observing the bacteria harvest and spectrometer operation, thanks to the great people there, which was very interesting. During my internship we were able to run several batches on the spectrometer but have not yet analyzed the results in detail.

Overall it was a great experience to handle the ice - particularly to hold something several thousand years old from several hundred meters below the surface of Antarctica and see the bubbles of atmosphere trapped in it. I am very happy to have been given the chance to be a part of Professor Alexander's research; not only do I have an increased interest in atmospheric science that I can take with me to finish my degree at Columbia and beyond, but I have spent my summer doing my best to contribute to a large climate record project, which is something I consider very worthwhile. I was also able to enjoy the summer near my hometown, in the beautiful city of Seattle.