Method for Quantification of Fatty Acids in Ice Cores and Sea-Ice Cores Using Liquid Chromatography High-Resolution Mass Spectrometry

Marine-sourced fatty acids provide a promising new suite of proxies for past sea-ice reconstructions, validated using ice cores from Bouvet Island, Greenland, and Alaska. Despite showing great potential as a sea-ice proxy, the transport, deposition, and preservation of these fatty acids within the ice sheet are poorly understood. Additionally, complementary data of the same suite of fatty acids in the source, the surrounding sea ice, is lacking in number, spatial distribution, and seasonal variety, especially in the Antarctic. This study presents an improved method using high-performance liquid chromatography high-resolution mass spectrometry (HPLC-HRMS) for the determination of marine-sourced fatty acids in ice cores and sea ice. The method presents a new preconcentration step using stir bar sorptive extraction (SBSE) as well as reduced background contamination using a trapping column tandem analytical system in HPLC. The method is suitable to detect and quantify a suite of 10 fatty acids with recoveries above 70% and with limits of detection in the low ppb and subppb levels. A range of fatty acids were detected and quantified in samples from two sub-Antarctic ice cores, taken from Peter first Island and Young Island. The results from these cores displayed a variety of fatty acids present in both ice cores (lauric acid, myristic acid, oleic acid, linoleic acid, palmitoleic acid, heptadecanoic acid, pentadecanoic acid, docosahexaenoic acid, eicosapentaenoic acid, and arachidonic acid) as well as a large difference in concentrations between different fatty acids and between the two ice cores. Additionally, this study presents the first results of fatty acid concentrations in the pancake sea ice collected from the Antarctic Marginal Ice Zone.