A new HPLC-MS method for fatty acid detection in sea ice

The presence of marine-sourced fatty acids1,2,3, in Antarctic ice cores has been linked to changes in sea ice conditions2,3. It has been proposed that the phytoplankton within and around the sea ice produce these fatty acids3 which are then released into the atmosphere upon sea-ice retreat and deposited onto the continental ice sheet2,3. While fatty acids show great potential as a proxy to reconstruct past sea ice, their transport, deposition and preservation within the ice sheet is poorly understood.  Few studies have investigated sea ice as a source of fatty acids and even fewer have investigated Antarctic sea ice4,5,6. Here we present a new study exploring the methods of detecting fatty acids in sea ice, including new results from pancake ice collected from the Antarctic Marginal Ice Zone in 2022.Analyses of fatty acids are typically carried out using gas chromatography (GC) coupled with mass spectrometric (MS) techniques6,7,8,9. With the rise of liquid chromatography methods in the past few decades, their use have become more common. High performance liquid chromatography (HPLC) has an advantage over GC methods with its lower temperatures during analysis, thus reducing the risk of altering or destroying the fatty acids10. A resultant HPLC-MS method, using electrospray ionisation, is presented for the detection and analysis of fatty acids in sea ice.[1] K. Kawamura et al., “Ice core record of fatty acids over the past 450 years in Greenland,” Geophysical Research Letters, vol. 23, pp. 2665-2668, 1996.[2] A. King et al., “Organic compounds in a sub-Antarctic ice core: A potential suite of markers” Geophysical Research Letters, vol. 46, pp. 9930-9939, 2019.[3] E. Thomas et al., “Antarctic Sea Ice Proxies from Marine and Ice Core Archives Suitable for Reconstructing Sea Ice over the past 2000 Years,” Geosciences, vol. 9, pp. 506-539, 2019.[4] K. Fahl and G. Kattner, "Lipid Content and fatty acid composition of algal communities in sea-ice and water ffom the Weddell Sea (Antarctica)," Polar Biology, vol. 13, pp. 405-409, 1993.[5] P. Nichols et al., "Occurence of an isoprenoid C25 diunsaturated alkene and high neutral lipid content in antarctic sea-ice diatom communities," Journal of Phycology, vol. 24, pp. 90-96, 1988.[6] D. Nichols et al., "Fatty acid, sterol and hydrocarbon composition of Antarctic sea ice diatom communities during the spring bloom in McMurdo Sound," Antarctic Science, vol. 5, pp. 271-278, 1993.[7] S. Wang et al., "Fatty acid and stable isotope characteristics of sea ice and pelagic particulate organic matter in the Bering Sea: tools for estimating sea ice algal contribution to Arctic food web production," Oecologia, vol. 174, pp. 699-712, 2014.[8] S. Wang et al., "Importance of sympagic production to Bering Sea zooplankton as revealed from fatty acid-carbon stable isotope analyses," Marine Ecology Progress Series, vol. 518, pp. 31-50, 2015.[9] E. Leu et al., "Spatial and Temporal Variability of Ice Algal Trophic Markers—With Recommendations about Their Application," Journal of Marine Science and Engineering, vol. 8, pp. 676, 2020.[10] E. Lima and D. Abdalla, "High-performance liquid chromatography of fatty acids in biological samples," Analytica Chimica Acta, vol. 465, pp. 81-91, 2002.