An inter-laboratory investigation of the Arctic sea ice biomarker proxy IP.sub.25 in marine sediments: key outcomes and recommendations

• Published in: Climate of the past Vol. 10; no. 1; pp. 155 - 309
• Main Authors: Belt, S. T, Brown, T. A, Ampel, L, Cabedo-Sanz, P, Fahl, K, Kocis, J. J, Massé, G, Navarro-Rodriguez, A, Ruan, J, Xu, Y
• Format: Journal Article
• Language: English
• Published: Copernicus GmbH 21.01.2014
• Subjects: Analysis; Investigations; Laboratory equipment; Marine sediments; Proxy; Sea ice
• ISSN: 1814-9332; 1814-9332

We describe the results of an inter-laboratory investigation into the identification and quantification of the Arctic sea ice biomarker proxy IP.sub.25 in marine sediments. Seven laboratories took part in the study, which consisted of the analysis of IP.sub.25 in a series of sediment samples from different regions of the Arctic, sub-Arctic and Antarctic, additional sediment extracts and purified standards. The results obtained allowed 4 key outcomes to be determined. First, IP.sub.25 was identified by all laboratories in sediments from the Canadian Arctic with inter-laboratory variation in IP.sub.25 concentration being substantially larger than within individual laboratories. This greater variation between laboratories was attributed to the difficulty in accurately determining instrumental response factors for IP.sub.25, even though laboratories were supplied with appropriate standards. Second, the identification of IP.sub.25 by 3 laboratories in sediment from SW Iceland that was believed to represent a blank, was interpreted as representing a better limit of detection or quantification for such laboratories, contamination or mis-identification. These alternatives could not be distinguished conclusively with the data available, although it is noted that the precision of these data was significantly poorer compared with the other IP.sub.25 concentration measurements. Third, 3 laboratories reported the occurrence of IP.sub.25 in a sediment sample from the Antarctic Peninsula even though this biomarker is believed to be absent from the Southern Ocean. This anomaly is attributed to a combined chromatographic and mass spectrometric interference that results from the presence of a di-unsaturated highly branched isoprenoid (HBI) pseudo-homologue of IP.sub.25 that occurs in Antarctic sediments. Finally, data are presented that suggest that extraction of IP.sub.25 is consistent between Accelerated Solvent Extraction (ASE) and sonication methods and that IP.sub.25 concentrations based on 7-hexylnonadecane as an internal standard are comparable using these methods. Recoveries of some more unsaturated HBIs and the internal standard 9-octylheptadecene, however, were lower with the ASE procedure, possibly due to partial degradation of these more reactive chemicals as a result of higher temperatures employed with this method. For future measurements, we recommend the use of reference sediment material with known concentration(s) of IP.sub.25 for determining and routinely monitoring instrumental response factors. Given the significance placed on the presence (or otherwise) of IP.sub.25 in marine sediments, some further recommendations pertaining to quality control are made that should also enable the two main anomalies identified here to be addressed.