FTIR imaging analysis of cell content in sea-ice diatom taxa during a spring bloom in the lower Northwest Passage of the Canadian Arctic

During their vernal bloom, ice algae respond to variable light and nutrient availability by changing their production of cellular lipids and proteins. Fourier transform infrared (FTIR) spectrochemical imaging was used to quantify relative amounts of saturated lipids and proteins within algal cells from high and low light conditions, i.e. thin and thick snow cover, respectively. Samples were collected within the lower Northwest Passage, near Cambridge Bay, Nunavut, Canada during the 2014 ICE-CAMPS field campaign. Diatom taxa analyzed included Nitzschia frigida, pennate ribbon colonies, and Attheya spp. Saturated lipid content and lipid to protein ratios were significantly greater under thin snow covers relative to those under thick; cell protein content remained relatively stable throughout the study under both snow covers. Results have been interpreted relative to a concurrent, related study wherein under-ice nutrients were concluded to be limited throughout the study. Taxa responses reported herein differed according to size, with N. frigida exhibiting the earliest and most dramatic changes. The increase in lipid to protein ratio highlighted the transitioning allocation of carbon from protein to lipid algal biomass through the spring bloom progression, with increasing light under nutrient limiting conditions in this location.