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

Abstract

Abstract. We describe the results of an inter-laboratory investigation into the identification and quantification of the Arctic sea ice biomarker proxy IP 25 in marine sediments. Seven laboratories took part in the study, which consisted of the analysis of IP 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 25 was identified by all laboratories in sediments from the Canadian Arctic with inter-laboratory variation in IP 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 25 , even though laboratories were supplied with appropriate standards. Second, the identification of IP 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 25 concentration measurements. Third, 3 laboratories reported the occurrence of IP 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 25 that occurs in Antarctic sediments. Finally, data are presented that suggest that extraction of IP 25 is consistent between Accelerated Solvent Extraction (ASE) and sonication methods and that IP 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 25 for determining and routinely monitoring instrumental response factors. Given the significance placed on the presence (or otherwise) of IP 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.

Highly branched isoprenoids for Southern Ocean sea ice reconstructions: a pilot study from the Western Antarctic Peninsula

“…cooler SSTs, sea ice cover, grazing pressure). Contrary to the finding of elevated HBI Z-triene concentrations in surface waters along an ice edge (Smik et al, 2016a) and earlier suggestions that this biomarker may be used as a proxy for MIZ conditions (Belt et al, 2015;Collins et al, 2013;Schmidt et al, 2018), we observe the highest concentrations of the HBI Z-and E-triene at the permanently ice-free northernmost stations PS97/083 and PS97/084 in the eastern Drake Passage. These core sites are located close to the Antarctic Polar Front (Fig.…”

“…Berben et al, 2014;Cabedo-Sanz et al, 2013;Müller et al, 2009Müller et al, , 2012Müller and Stein, 2014;Stein et al, 2017;Xiao et al, 2015). A comparison of PIP 25 records determined using brassicasterol and the HBI Z-triene for three sediment cores from the Arctic realm covering the past up to 14 000 years BP (Belt et al, 2015) reveals very similar trends for both versions of the PIP 25 index in each core, which may point to, at least, a similar degree of degradation of HBI trienes and sterols through time. More such studies are needed to evaluate the preservation potential of HBIs and sterols in Southern Ocean sediments, especially for down core paleo-studies.…”

MIS 3 to MIS 1 temporal and LGM spatial variability in Arctic Ocean sea ice cover: Reconstruction from biomarkers

“…Here we use a quite novel molecular sea ice proxy consisting of 25 carbon atoms-so-called IP 25to reconstruct past sea ice conditions in the Arctic Ocean. This compound is a monounsaturated highly branched isoprenoid alkene biosynthesized by specific Arctic sea ice diatoms [Brown et al, 2014], which was first determined in Canadian Arctic sediments and sea ice by Belt et al [2007]. Meanwhile, IP 25 has been universally used in marine sediments for sea ice reconstruction (for reviews, see Belt and Müller [2013] and Stein et al [2012, and references therein]).…”

“…Meanwhile, IP 25 has been universally used in marine sediments for sea ice reconstruction (for reviews, see Belt and Müller [2013] and Stein et al [2012, and references therein]). The extraction, identification, and quantification of IP 25 have been well established and intercalibrated between different laboratories [Belt et al, 2012. IP 25 studies using Figure 1.…”

On the stability of various highly branched isoprenoid (HBI) lipids in stored sediments and sediment extracts

“…The quality of the outcomes from such studies relies on the accurate identification and quantification of individual HBIs, which has been made possible by the previous reporting of key chromatographic and mass spectral data (e.g., Johns et al, 1999;Belt et al, 2000;Brown et al, 2014). In a previous inter-laboratory investigation of IP25 in Arctic sediments, however, a number of analytical pitfalls were identified, which provided the basis for proposing a standard operating procedure for future studies (Belt et al, 2014). However, that study was conducted on carefully stored (-20°C) sediment material, with no consideration given to the potential impacts of variable storage conditions, either for sediments or sediment extracts.…”