Trophic marker composition of Arctic zooplankton and Polar cod sampled under sea ice and throughout the water column of the Central Arctic Ocean during the MOSAiC expedition (2019/2020)

At the basis of the marine Arctic food web, there are several carbon sources including ice-associated (sympagic) algae that live primarily in sea ice, melt ponds or underneath sea ice; pelagic algae that live primarily in open waters; terrestrial detritus that got incorporated into sea ice forming on the Siberian Shelf and being transported with the transpolar drift across the Central Arctic Ocean (CAO); and detritus that derives with currents from the Atlantic ocean. Copepods and amphipods are diverse and often biomass-dominant zooplankton groups in the CAO that include taxa specialised in feeding on algae and small heterotrophs, on sinking detritus or other zooplankton. Gelatinous (cnidaria, appendicularia) and semi-gelatinous (chaetognaths) taxa, ostracods, pteropods, euphausiids and pelagic decapods are other important zooplankton groups in the CAO that likewise feed on a range of food sources. With the loss of Arctic sea ice, the relative importance of ice-associated carbon in the Arctic food web became a central research topic, and multiple trophic marker approaches have been developed to distinguish between pelagic and sympagic carbon transfer to higher trophic levels.

During the MOSAiC expedition in the CAO (2019-2020), zooplankton was sampled weekly to fortnightly. A range of nets were used to sample either horizontally underneath the sea ice or vertically from a maximum depth of 2000 m to the surface. Onboard, abundant zooplankton taxa were sorted from each catch, photographed, rinsed with freshwater to remove salt and frozen at -80 degrees Celsius for subsequent analysis of their total dry mass (DM), lipid content, lipid classes and a suite of trophic markers, including bulk stable isotopes (BSI), phytosterols (PS), total fatty acids (TFA), total fatty alcohols (TFAlc), highly-branched isoprenoids (HBI) and the carbon isotopic composition of key FA and FAlc (CSIA-FA; CSIA-FAlc). We had ~10 target species that were sampled in all seasons (the copepods C. hyperboreus, C. glacialis, Metridia longa, the ice amphipods Apherusa glacialis and Eusirus spp., the pelagic amphipods Themisto abyssorum and T. libellula, the euphausiid Thysanoessa spp., chaetognaths and the shrimp H. glacialis). Further zooplankton taxa were collected when available in the net catches and time permitted. Additionally, Polar cod was collected in early and late summer.

The initial separation of the various trophic markers was carried out at the University of Plymouth. After estimating the total DM, subsamples for BSI were sent to the Littoral, Environment and Societies Joint Research Unit stable isotope facility (CNRS - University of La Rochelle, France) for analysis. Three internal standards were added to the samples used for lipid analysis to quantify the TFA, TFAlc, PS and HBI content. As a first step, the total lipid content of the animals was extracted in dichloromethane : methanol. The lipid samples were split into two equal subsamples, one was sent to the Alfred-Wegener-Institute (AWI) in Bremerhaven/Germany for FA and FAlc analyses and the second was used for PS and HBI analyses in Plymouth.

This dataset is linked to a manuscript that assesses trophic relationships in the CAO to understand the carbon fluxes in the current Arctic food web and to predict potential changes in a future ice-free Arctic.

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). CJA, RGC, CEG, KMS and RJ were funded by the US National Science Foundation Office of Polar Programs (OPP-1824447 and OPP-1824414).

Alternate title: Polar Data Centre (PDC) record GB/NERC/BAS/PDC/02068

Date (Publication): 2025-05-30

Citation identifier: http://www.antarctica.ac.uk/dms/metadata.php?id= / GB/NERC/BAS/PDC/02068

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., Graeve, M., Lebreton, B., Welteke, N., Woll, M., & Guillou, G.	pdc@bas.ac.uk	Originator

Maintenance and update frequency: Unknown

Keywords

NDGO0001

NERC OAI Harvesting

NERC_DDC

GCMD Parameter Valids

EARTH SCIENCE > Oceans > Marine Environment Monitoring
EARTH SCIENCE > Oceans > Ocean Chemistry > Hydrocarbons

BAS Free-text keywords

δ13C
δ15N
Arctic zooplankton
BSIA
CSIA
Central Arctic Ocean (CAO)
MOSAiC
Polar cod
fatty acids
fatty alcohols
lipids
trophic marker

Use limitation: Data are supplied under Open Government Licence v3.0 http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/.

Access constraints: Other restrictions

Other constraints: Data are supplied under Open Government Licence v3.0 http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/.

Language: English

Topic category

Environment
Oceans

Begin date: 2019-11-04

End date: 2020-09-27

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 restrictions on ship-time, replicate net tows were not feasible. The same is true for the sorting of animals onboard: to cover all the selected target species and parameters in a timely manner, only one sample per species and developmental stage was prepared for trophic marker analysis. From the dried material only one sample was prepared for each BSI and lipid analysis, but a small back-up of dried material was kept in case one of the analyses failed. A very few BSI samples had to be repeated due to problems with the autosampler, while all lipid analyses were carried out successfully at first attempt. Therefore, the back-up material was subsequently used for tissue density analysis. The FA and FAlc profiles were compared to both commercial- (Supelco 37 Component FAME mix, Supelco, Germany) and self-produced standards (e.g. Arctic algae standard, bacteria standard, Calanus spp. standard), and were identified accordingly. In a few cases, samples were also analysed with the mass spectrometer and peaks were identified via (1) the mass of the compound, (2) the retention time of the compound and (3) the equivalent chain length method. For sterols, cultured algae of known sterol composition were used to clarify the identity of the five phytosterol peaks. Therefore, the mass spectra of their trimethylsilylethers were compared with published data. For several samples, parallel analysis of the extracts was carried out at the AWI, benefitting from the long-term experience in sterol identification by our colleague Dr. Kirsten Fahl. The uncertainty of the reported isotope-delta values (BSI) was evaluated as the standard deviation of repeated measurements (n = 5) for the reference material, USGS61 and USGS63 (Geological Survey, Reston, VA, USA), based on their assigned carbon and nitrogen isotope-delta values and standard uncertainties. For our measurements the uncertainty did not exceed 0.10 per mille for both delta13C and delta15N values. The delta13C values of the individual FAMEs were calibrated by analysing the certified standard FAMEs 14:0 (certified delta13C value: -29.98 per mille, measured delta13C value: -29.54 per mille) and 18:0 (certified delta13C value: -23.24 per mille, measured delta13C value: -23.29 per mille) at regular intervals (~ every five samples). The analytical error was ± 0.3 per mille for both 14:0 and 18:0 (representing 1 standard deviation of 10 analyses each). Furthermore, for quality assurance and analytical precision of the determined carbon stable isotope composition, the laboratory standard 23:0 was measured intermittently during the sample runs with an analytical error of ± 0.4 per mille (representing the standard deviation of 10 analyses).