Carbonyl sulfide measurements in the GISP2D ice core from Summit, Greenland
Polar ice cores contain an archive of ancient air that can be used to reconstruct history of atmospheric gas composition. This project involves analysis of samples from the GISP2D ice core drilled at Summit, Greenland, and will develop an atmospheric history of carbonyl sulfide (COS). Variations in atmospheric COS can be linked to growth of plants on land because they take up COS from the atmosphere during photosynthesis. The Greenland ice core record of COS from this project will be used to document possible changes in terrestrial plant growth over the last 1000 years and to constrain the natural controls on stratospheric sulfate aerosol layer. This project will support training of a doctoral student at UC Irvine and provide hands-on research experience for several undergraduate students in a state-of-the-art analytical chemistry laboratory. It will also support K-12 outreach activities by the UC Irvine ice core laboratory in local middle and high schools through the CLEAN Education initiative, a non-profit founded and operated by graduate students at UC Irvine. The investigators previously measured COS in ice cores from several different Antarctic sites, recovering COS records of the southern hemisphere atmosphere over periods that range from centuries to multi-millennia. As part of this project, they will measure 140 samples from the GISP2D ice core and create the first ice core COS record of the northern hemisphere atmosphere spanning the last 3000 years. Ice core air will be dry-extracted and analyzed with an existing gas chromatography-mass spectrometry (GC-MS) system. COS lifetime in the atmosphere is only 2 years and its atmospheric budget is poorly understood. Estimates of COS removal from the atmosphere via photosynthesis by land plants far exceed the known emissions, possibly pointing to an unidentified natural source. Modeling work suggests knowing the pole-to-pole COS difference in the preindustrial atmosphere would provide a robust constraint on the nature and magnitude of the unidentified source(s). The GISP2D measurements for the last 1000 years before present will be conducted at high-resolution. This includes the Little Ice Age period, during which Antarctic ice core records display a decline in atmospheric COS. The new Greenland measurements will constitute a northern hemisphere analogue to existing Antarctic records. Results will be used to study climate driven variability in atmospheric COS and implications for changes in plant growth and variability in background stratospheric sulfate in the preindustrial atmosphere. The project includes plans for a comprehensive modelling effort with a 6-box model of the atmosphere, which will be coupled to ocean and terrestrial vegetation models. Measurements from 3000 to 1000 years before present will be conducted at lower resolution and the primary goal will be to gain further insight into the slow in-situ hydrolysis loss of COS in ice cores that has been previously observed in Antarctic ice cores over multi-millennial time scales.