An inter-laboratory investigation of the Arctic sea ice biomarker proxy IP<sub>25</sub> in marine sediments: key outcomes and recommendations
We describe the results of an inter-laboratory investigation into the identification and quantification of the Arctic sea ice biomarker proxy IP<sub>25</sub> in marine sediments. Seven laboratories took part in the study, which consisted of the analysis of IP<sub>25</sub> in...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-01-01
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| Series: | Climate of the Past |
| Online Access: | http://www.clim-past.net/10/155/2014/cp-10-155-2014.pdf |
| Summary: | We describe the results of an inter-laboratory investigation into the
identification and quantification of the Arctic sea ice biomarker proxy
IP<sub>25</sub> in marine sediments. Seven laboratories took part in the study, which
consisted of the analysis of IP<sub>25</sub> 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</sub> was identified by all
laboratories in sediments from the Canadian Arctic with inter-laboratory
variation in IP<sub>25</sub> 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</sub>, even though laboratories were supplied with
appropriate standards. Second, the identification of IP<sub>25</sub> 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</sub> concentration
measurements. Third, 3 laboratories reported the occurrence of IP<sub>25</sub> 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</sub> that occurs in Antarctic sediments. Finally,
data are presented that suggest that extraction of IP<sub>25</sub> is consistent
between Accelerated Solvent Extraction (ASE) and sonication methods and that
IP<sub>25</sub> 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</sub> for determining and routinely
monitoring instrumental response factors. Given the significance placed on
the presence (or otherwise) of IP<sub>25</sub> 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. |
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| ISSN: | 1814-9324 1814-9332 |