My name is Laura Moore, and I am a senior chemistry major at St. Olaf College in Northfield, Minnesota. This summer I worked with Dr. Becky Alexander and her graduate student John Robinson studying oxygen isotopes in an ice core taken from the West Antarctic Ice Sheet.
Ice cores provide extensive records of earth’s climate via the chemical species preserved in the core, and scientists can analyze these chemicals to reconstruct what past climatic conditions may have looked like. My project focused on examining two atmospheric oxidants’ (O3 and OH) responses to rapid climate change events during the period of 36,000 to 52,000 years before present.
The oxidants of interest, O3 and OH, are not actually preserved in ice cores so instead we measured oxygen isotopes from a proxy, NO3–. By measuring the isotopic composition of oxygen in the preserved NO3–, we obtain a proxy for the ratio of O3 to OH, the ∆17O(NO3–) value. This value is then used to evaluate the response of atmospheric oxidants to rapid climate change events
Understanding the behavior of atmospheric oxidants is important because they are capable of reacting with a variety of trace gases to clean the air. As such, given current anthropogenic emissions of pollutants, knowledge of the oxidants’ behavior during past climate change events is critical. Previous observations from a Greenland ice core show significant changes in oxidant abundances over rapid climate change events. We analyzed the Antarctic ice core to determine whether there are hemispheric differences in oxidant abundances.
Obtaining the ∆17O(NO3–) value required extensive sample preparation before final analysis on a mass spectrometer for isotopic composition. The most memorable step of the sample process though is probably the first, which involves donning many layers of warm clothing and walking into a -7oC freezer to cut pieces of the ice core. The rest of sample preparation, thankfully, occurred at room temperature outside the freezer!
By the end of the summer, we found that unlike in Greenland, the ∆17O(NO3–) value does not exhibit temperature dependent behavior over rapid climate change events in the Antarctic core. The exact reason behind this hemispheric difference though, is uncertain at present.
Over the course of the summer, I gained many valuable research skills— in particular learning how to use a mass spectrometer and an ion chromatograph (although learning to use a band-saw was quite fun too). Being from a small college in Minnesota, the opportunity to intern with the JISAO program at a large research university was an amazing experience. Working with the Alexander group was a wonderful introduction to atmospheric chemistry, and I am definitely going to consider the field for future endeavors!