Structural confirmation of the sea ice biomarker IP25 found in Arctic marine sediments

IP25 is a highly branched isoprenoid and an organic geochemical biomarker that is produced by some Arctic sea ice diatoms. IP25 has previously been used in Arctic palaeo sea ice reconstruction studies and as a tracer for studying Arctic food webs. Here, the molecular structure of IP25 has been confirmed by H-1 and C-13 NMR spectroscopy following large-scale extraction from marine sediments obtained from the Canadian Arctic and purification using a combination of open-column and HPLC chromatographic methods. The structure of IP25 was consistent between the three different sampling locations and was identical to that found previously for this biomarker following synthesis from a closely related highly branched isoprenoid diene. Since this study represents the first structural characterisation of IP25 in sediments, future analysis of sedimentary IP25 for palaeo Arctic sea ice reconstructions can be carried out with much greater confidence.