Fatty acids and stable isotope signatures of first-year and multiyear sea ice in the Canadian High Arctic

Ice algae are critical components to the lipid-driven Arctic marine food web, particularly early in the spring. As little is known about these communities in multiyear ice (MYI), we aimed to provide a baseline of fatty acid (FA) and stable isotope signatures of sea-ice communities in MYI from the Lincoln Sea and compare these biomarkers to first-year ice (FYI). Significant differences in the relative proportions of approximately 25% of the identified FAs and significantly higher nitrogen stable isotope values (δ15N) in bottom-ice samples of FYI (δ15N = 6.4 ± 0.7%) compared to MYI (δ15N = 5.0 ± 0.4%) reflect different community compositions in the two ice types. Yet, the relative proportion of diatom- and dinoflagellate-associated FAs, as well as their bulk and most of the FA-specific carbon stable isotope compositions (δ13C) were not significantly different between bottom FYI (bulk δ13C: –28.4% to –26.7%, FA average δ13C: –34.4% to –31.7%) and MYI (bulk δ13C: –27.6% to –27.2%, FA average δ13C: –33.6% to –31.9%), suggesting at least partly overlapping community structures and similar biochemical processes within the ice. Diatom-associated FAs contributed, on average, 28% and 25% to the total FA content of bottom FYI and MYI, respectively, indicating that diatoms play a central role in structuring sea-ice communities in the Lincoln Sea. The differences in FA signatures of FYI and MYI support the view that different ice types harbor different inhabitants and that the loss of Arctic MYI will impact complex food web interactions with ice-associated ecosystems. Comparable nutritional quality of FAs, however, as indicated by similar average levels of polyunsaturated FAs in bottom FYI (33%) and MYI (28%), could help to ensure growth and reproduction of ice-associated grazers despite the shift from a MYI to FYI-dominated sea-ice cover with ongoing climate warming.