The Arctic sea ice proxy, IP25, in particulate organic matter (POM) from surface waters and bottom sea-ice of the Central Arctic Ocean during the MOSAiC expedition in 2019/2020

During the MOSAiC expedition in the Central Arctic Ocean (CAO, 2019-2020), POM was sampled weekly to fortnightly from surface waters and the Chlorophyll a maximum layer (Chl a max) via CTD casts and from bottom sea ice of the floe via ice coring (first- and second-year ice, two layers nearest to the water-ice interface). The POM was filtered onboard (GF/F filters) and deep frozen for the subsequent analysis of a suite of lipid biomarkers, including IP25 and other highly-branched isoprenoids (HBI), fatty acids (FA) and sterols. These biomarkers can provide valuable information about the nutritional value, the taxonomic composition (e.g. diatoms vs flagellates), and the origin of the POM that represents the basis of the Central Arctic food web. This dataset comprises the results from the HBI analysis only, while the FA dataset is already published and the sterol data will be submitted shortly. The separation of the various lipid biomarkers was carried out at the University of Plymouth. After addition of internal standards for each of the 3 components, the filters were saponified with KOH.

Thereafter, non-saponifiable lipids (HBI and sterols) were extracted with hexane and purified by open column chromatography (SiO2). Fatty acids were obtained by adding concentrated HCl to the saponified solution and re-extracted with hexane. The analysis of IP25 was carried out using an Agilent 7890A gas chromatograph (GC), coupled to an Agilent 5975 mass selective detector (mass spectrometry, MS), fitted with an Agilent HP-5ms column with auto-splitless injection and helium carrier gas. Identification of IP25 and other HBIs was achieved by comparison of their individual GC retention indices and mass spectra with those obtained from purified standards. IP25 was quantified by, first, integrating individual ion responses in selected-ion monitoring mode (m/z 350.3), second, normalising these to the corresponding peak area of the internal standard and, third, applying an instrumental response factor obtained from a purified standard. These IP25 quantities per filter can be normalised to the volume of filtered seawater or melted ice core water.

Contributions by KS were funded by the UK''s Natural Environment Research Council MOSAiC Thematic project SYM-PEL: ''''Quantifying the contribution of sympagic versus pelagic diatoms to Arctic food webs and biogeochemical fluxes: application of source-specific highly branched isoprenoid biomarkers''''/ (NE/S002502/1)

Alternate title: Polar Data Centre (PDC) record GB/NERC/BAS/PDC/01783

Date (Publication): 2024-01-17

Citation identifier: http://www.antarctica.ac.uk/dms/metadata.php?id= / GB/NERC/BAS/PDC/01783

Point of contact

Organisation name	Individual name	Electronic mail address	Role
British Antarctic Survey		pdc@bas.ac.uk	Custodian
NERC EDS UK Polar Data Centre	Schmidt, K., Belt, S., Graeve, M., Hildebrandt, N., Fong, A., Castellani, G., Hoppe, C., Atkinson, A., & Vortkamp, M.	pdc@bas.ac.uk	Originator

Maintenance and update frequency: Unknown

Keywords

NDGO0001

NERC OAI Harvesting

NERC_DDC

GCMD Parameter Valids

EARTH SCIENCE > Oceans > Ocean Chemistry
EARTH SCIENCE > Oceans > Ocean Chemistry > Carbon
EARTH SCIENCE > Oceans > Ocean Chemistry > Chlorophyll

BAS Free-text keywords

Central Arctic Ocean (CAO)
IP25
MOSAiC
bottom sea ice
chlorophyll a maximum
highly-branched isoprenoids (HBI)
lipid biomarker
particulate organic matter
surface waters

Use limitation: Data released under Open Government Licence V3.0: http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/.

Access constraints: Other restrictions

Other constraints: Data released under Open Government Licence V3.0: http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/.

Language: English

Topic category

Biota

Begin date: 2019-11-04

End date: 2020-09-25

Reference system identifier: OGP / urn:ogc:def:crs:EPSG::4326

Distribution format

Distributor contact

Organisation name	Individual name	Electronic mail address	Role
Polar Data Centre - British Antarctic Survey		pdc@bas.ac.uk	Distributor

OnLine resource

Protocol	Linkage	Name
http		GET DATA

Hierarchy level: Dataset

Domain consistency

Measure identification: INSPIRE / Conformity_001

Conformance result

Title: INSPIRE Data Specification on unknown theme Guidelines

Date

Explanation: See the referenced specification

Pass: No

Statement: Due to the low concentrations of POM in the water column, the volumes that needed to be filtered were often >10 L and filtration of replicate samples was not feasible. The HBI GC-MS profiles were compared to those from purified standards obtained from previous laboratory diatom cultures (e.g. IPSO25, HBI Trienes Z and E) and Arctic sediment extracts (IP25), and peak areas were normalised to those of a laboratory synthesised internal standard (e.g. 9-octyl-8-heptadecene) for quantification purposes. The four key HBIs can be separated via their number of double-bonds using the following mass spectral ions: m/z 350.3 for the monoene, IP25; m/z 348.3 for the diene, IPSO25; and m/z 346.3 for the two trienes, HBI III - Z and HBI III - E. However, in this set of samples, we did not find any HBI trienes. Moreover, the HBI diene IPSO25, although often present, was not quantifiable due to a combination of low abundances and/or chromatographic overlap with other HBIs. Further, previous studies have shown that IPSO25 is susceptible to rearrangement in some environmental samples (e.g. Belt and Cabedo-Sanz 2015), thus making it difficult to estimate the absolute amount of IPSO25. This appears to be the case in the samples analysed, therefore we note here that IPSO25 was produced in the CAO, but was non-quantifiable. In contrast, the monoene IP25 is the least reactive of the four considered HBIs and could be readily quantified.