Dynamics of dissolved carbohydrates during the spring sea ice melt season in the Canadian Arctic

In spring 2016, the temporal evolution of organic carbon and carbohydrate concentrations was monitored in and under the sea ice during the microalgal–ice algae and subsequent phytoplankton–productive periods in western Baffin Bay (Canadian Arctic). The results showed that total carbohydrates (TCHO) closely followed total organic carbon, with the highest concentrations observed in the bottom-most few centimeters of sea ice (mean 186 µM C, n = 22). Such organic matter accumulation likely comprises labile organic matter, reflecting the presence of a concentrated algal biomass, as suggested by the significant correlation between TCHO and chlorophyll a ( r = 0.625, p < 0.05). Compositionally, the bottom-most ice core was dominated by monosaccharides, which accounted for 38%–90% of TCHO, and were probably the result of an important in situ exoenzymatic activity of polysaccharides. Conversely, total dissolved carbohydrates in the underlying water did not follow dissolved organic carbon patterns and were dominated by dissolved polysaccharides, indicating that carbohydrates may have multiple sources, not solely from microalgae in either pelagic or sympagic (ice-associated) environments. Overall, our results suggest significant differences in carbohydrate dynamics between sea ice and the under-ice water, despite the strong coupling of these systems during ice melt, highlighting the complexity of the processes occurring within these ecosystems.