| Summary: | A recent study demonstrated that a tidal strait, where a shoaled and constricted waterway increases tidally driven sub-ice currents and turbulence, represent ice algal production hotspots due to a hypothesized enhanced ocean-ice nutrient supply. Based on these findings, we sampled the bottom-ice algal community across the same tidal strait between the Finlayson Islands within Dease Strait, Nunavut, Canada in spring 2017. Our objective was to examine sea ice diatom cellular responses to two expected nutrient supply gradients in their natural environment: (1) a spatial gradient across the tidal strait and (2) a vertical gradient up into the bottom-ice matrix. Two diatom taxa, Nitzschia frigida and Attheya spp. within the bottom-ice sections (0-2, 2-5, and 5-10 cm) under thin snow cover (<5 cm) were selected for Fourier Transform Infrared (FTIR) spectrochemical analysis for lipid and protein content. Results from the FTIR technique strongly supported the existence of a spatial nutrient gradient across the tidal strait of the Finlayson Islands, while particulate organic carbon (POC) and chlorophyll a (Chl a) concentration estimates were difficult to interpret. Spatially, the larger N. frigida cells appeared to be more sensitive to the nutrient gradient, significantly increasing (decreasing) in lipid (protein) content towards the outside of the tidal strait. In contrast, the epiphytic diatom, Attheya spp., was more sensitive to the vertical gradient, where above 2 cm into the bottom-ice matrix, the non-motile cells were trapped with a depleted nutrient inventory and evidence of a post-bloom state. Application of the FTIR technique to estimate algal cell biomolecular composition provided new insights on the response of the bottom-ice algal community to the examined nutrient supply gradients that could not be attained from conventional bulk measurements alone. Therefore, future studies are encouraged to employ the use of this technique. Dataset consists of multiple tabs: 1. Metadata 2. Nitzschia frigida data 3. Attheya spp. data 4. Ice Algae Community 5. Diatom Population 6. FTIR Target Cells 7. Nutrients 8. POC & Chl a 9. PAR 10. Snow & Ice measurements
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