10.1594/PANGAEA.987865Leu, EvaEvaLeu0000-0002-5328-3396Akvaplan-nivaŠupraha, LukaLukaŠupraha0000-0003-2613-945XNorwegian Institute for Water ResearchGraeve, MartinMartinGraeve0000-0002-2294-1915Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, BremerhavenFahl, KirstenKirstenFahl0000-0001-9317-4656Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, BremerhavenMüller, AnjaAnjaMüllerAlfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, BremerhavenMüller, JulianeJulianeMüller0000-0003-0724-4131Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, BremerhavenLunden, JonasJonasLundenAlfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, BremerhavenWoll, MatthiasMatthiasWollAlfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, BremerhavenKohlbach, DoreenDoreenKohlbach0000-0002-9245-2500Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, BremerhavenPANGAEA2026Arctic microalgaeMelosiraStandard cultivationSterolstrophic markersEvent labelStation labelType of studySample code/labelDEPTH, waterDepth commentGenus, unique identificationGenus, unique identification (Semantic URI)Genus, unique identification (URI)24-Methylcholesta-5,22E-dien-3beta-ol24-methylcholest-5-en-3beta-ol3beta-Stigmast-5-en-3-olCholesta-5,24-dien-3beta-olDate/time start, experimentDate/time end, experimentExperimental treatmentTreatment: temperatureTreatment: salinityTreatment: nitrateTreatment: silicateTreatment: phosphateHand pumpReference in WoRMSGas chromatograph-mass spectrometerUnialgal cultures cultivationAO2023-1Kronprins Haakon2023-06-18T00:00:00Dataset10.1016/S0021-9258(18)64849-510.1038/s41467-025-59112-7171 data pointstext/tab-separated-valuesCreative Commons Attribution 4.0 InternationalData access is restricted (moratorium, sensitive data, license constraints)During the AO2023-1 expedition (1-21 June 2023), Melosira assemblages were collected using a handpump at a sampling site in Fram Strait. In addition to performing physiological measurements and filtering the material for trophic markers (fatty acids, stable isotope ratios of fatty acids, sterols and highly branched isoprenoids (HBIs), living material was brought back to Akvaplan-niva in Oslo and two strains were established as unialgal cultures. The cultures are maintained in artificial seawater-based L1 medium at 4°C and 25 µmol m-2 s-1 light with a 16:8 L:D cycle. Lipids were extracted from freeze-dried samples following the method of Folch et al. (1957), using a dichloromethane/methanol mixture (2:1, v/v) in a sonication bath. Thereafter, lipids were saponified with 20% potassium hydroxide in water/methanol (1:9). Sterols were extracted with hexane, purified by open-column chromatography with SiO2 and eluted with methanol. Sterol fractions were derivatized using N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA). Sterols were analyzed with gas chromatography–mass spectrometry (Agilent 7890B, Agilent Technologies), equipped with a DB-1ms column (30 m length, 0.25 mm internal diameter, 0.25 μm film thickness) and an Agilent 5977A MSD, following Stein et al. (2025). The temperature program ranged from 60°C to 320°C. Sterols were quantified using an internal standard (androstanol). Sterol analysis was conducted to complement datasets on fatty acid proportions and fatty acid stable isotope compositions. Collectively, the datasets enable a detailed characterization of the biochemical composition of different Melosira arctica-dominated algal assemblages from the Arctic Ocean, and a comparison with a unialgal culture of this important species.-2.138778.9397Fram StraitHorizon Europehttps://doi.org/10.13039/100018693101136875Ocean and coastal waters carbon- and biodiversity-rich ecosystems and habitats in Europe and the Polar Regions - HORIZON-CL6-2023-CLIMATE-01-3The FRAM Centrehttps://doi.org/10.13039/5011000223492551323Sustainable Development of the Arctic Ocean (SUDARCO)