Shrinking sea ice - reconstructions from ice cores

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Sea ice plays a vital role in modulating climate. Satellite observations reveal that Antarctic sea ice is at its lowest in 40 years. In the Bellingshausen Sea, adjacent to the Antarctic Peninsula, sea ice decline has been accompanied by warming surface temperatures and accelerated ice loss. These changes have a direct impact on global sea levels and thus understanding the significance of sea ice decline, and its role in modulating regional climate, is of global significance. However, observations of Antarctic sea ice are limited to the satellite era (post 1970) and climate models struggle to capture the observed trends. The lack of long-term observations is hindering our ability to place the recent changes in the context of natural variability or provide realistic boundary conditions for climate models tasked with predicting future climate change. Sea salts and other chemical species contained in ice cores provide the optimum method of reconstructing sea ice beyond the instrumental period. Advances in analytical capability, together with the collection of new coastal Antarctic ice cores, provides a unique opportunity to develop novel sea ice proxies and produce the first regional reconstructions over centennial timescales. The goal of this project is to produce regional sea ice reconstructions in key ocean sectors over the past 200-300 years. Organic compounds, such as fatty acids, have been proposed as a new proxy for sea ice [1]. Together with existing sea ice proxies [2], we now have the potential to produce multi-proxy reconstructions. This project will measure new organic compounds from a number of ice cores from coastal Antarctica and the sub-Antarctic islands. The data will be evaluated against inorganic species, such as bromide and sodium, to investigate changes in sea ice during different seasons (summer/ winter) and conditions (first-year or multi-year sea ice). The analytical aspect is complemented by chemical transport modelling to understand the source and transport pathways of chemical species [3]. This goes beyond the state-of-the-art by providing a robust method to calibrating sea ice proxies. The student will sub-sample existing and planned Antarctic ice cores for organic and inorganic analysis, in the -20C cold laboratories and class-100 cleanroom. The samples will be pre-concentrated and analysed at the Department of Chemistry, following a proven method developed by the project team. The project is not dependent on the collection of new ice cores; however we will endeavour to include the student in future drilling projects.In parallel to this analytical work, the student will carry out experiments using an atmospheric dispersion model and a chemical transport model to better understand the processes controlling the chemical signatures measured and fingerprint the source of aerosol deposited at ice core locations. The chemical transport model, now optimised to simulate sea salt concentrations of ice cores taking into account important emissions from the sea ice surface, will be used to test the relative influence of processes such as transport efficiency and emissions strength. Depending on the student's interests, there are opportunities to add new capability to simulate the atmospheric transport and chemistry of bromide, MSA and other organic species.