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IP25 is a highly branched isoprenoid lipid biomarker that is produced by some Arctic sea ice diatoms in the spring. The presence of IP25 in marine sediments has previously been used as a proxy measure of past spring sea ice occurrence in the Arctic. Here, a reliable analytical procedure for the reproducible extraction, identification and quantification of IP25 from marine sediments is presented for the first time. This protocol represents a Standard Operating Procedure (SOP) that should be straightforward to adopt by other researchers in the future. This paper also explains the significance of individual components and steps, including the internal standards used for quantification of IP25, the purification of sediment extracts to simplify the subsequent analysis and some key analytical considerations, especially when mass spectrometric methods are used for detection and quantification. The application of the SOP is illustrated with the analysis of IP25 in sediment material obtained from two nearby locations in the western region of the Canadian Arctic Archipelago (CAA). In the first case (Franklin Bay), sediment material was homogenised and aliquots used to demonstrate the reproducibility of the SOP and to provide a suitable reference material when studying other cores. In the second case (central Amundsen Gulf), IP25 concentrations were shown to be quite variable, consistent with observations reported previously for sediment cores from other regions of the CAA. Further experimental considerations are presented that permit the conversion of sedimentary IP25 concentrations into temporal fluxes that are probably more useful for palaeo sea ice studies.
Belt et al. (Sun,) studied this question.