Fatty acid composition, ice chemistry and algae biomass during an Arctic sea ice algal bloom on landfast ice near the settlement of Svea, in Van Mijenfjorden, Spitsbergen

The relative importance of sea ice algal-based production is often vital for studies about climate change impacts on Arctic marine ecosystems. The relevance of sea ice algal production for different parts of the polar ecosystem, ranging from key pelagic grazers to mammals and assessing the overall strength of sympagic-pelagic or sympagic-benthic coupling has been extensively studied. The key interest in all these studies is quantifying the relative importance of biomass produced by sea ice algae (as opposed to phytoplankton) for higher trophic level production. Different types of trophic markers are widely applied to analyse food web structure, based on numerous assumptions of how sea ice algae differ biochemically from phytoplankton. Several types of lipid biomarkers and stable isotope ratios are widely used for tracing sea ice associated (sympagic) vs. pelagic particulate organic matter (POM) in marine food webs. Beside the typical proximate data (POC, Chl-a, DIC, Biomass), we analysed fatty acids, highly branched isoprenoids (HBIs), stable isotope ratios of particulate organic carbon (POC) (δ13C), as well as δ13C of selected marker fatty acids during an Arctic sea ice algal bloom, focusing on spatial and temporal variability. Sampling was conducted on landfast ice near the settlement of Svea, in Van Mijenfjorden, Spitsbergen from 7 April to 5 May. A sea ice observatory was installed close to the deepest part of the inner basin on 8th of March providing background data for the entire study period on sea ice thickness, snow cover, and transmittance. Sea ice algal development was followed by sampling different stations in the inner basin from early March to early May 2017, including a spatial distribution along a transect starting from a very shallow station close to the shore (IS) to the mid-fjord station VMF2. The aim of our study was to document the spatial and temporal variability of different lipid and stable isotope-based trophic markers during an ice algal spring bloom and relate it to environmental conditions, as well as taxonomic composition. We then use these data to compare and contrast the reliability of each approach to distinguish between sympagic and pelagic POM.