Patterns and drivers of carbohydrate budgets in ice algal assemblages from first year <scp>A</scp>rctic sea ice

<jats:title>Abstract</jats:title><jats:p>Ongoing changes in sea ice distribution will have major implications for the ecology of the Arctic Ocean. First year ice (FYI) supports abundant ice‐algae communities that produce dissolved and particulate carbohydrates, including extracellular polymeric substances (EPS), which are significant carbon sources, influence ice formation and microbial survival within sea ice, and water column carbon cycling following ice melt. Key drivers of the distribution and composition of these carbohydrates are poorly characterised. Carbohydrates and chlorophyll <jats:italic>a</jats:italic> concentrations were linearly related in springtime bottom FYI at 36 sites in the Canadian Archipelago region, with high levels of spatial heterogeneity. Nanoeukaryote cell density and phosphate concentration were strong drivers of total and dissolved carbohydrate and uronic acid concentrations. Particulate carbohydrates were strongly related to total bacterial abundance. Dissolved carbohydrates contributed 77% of total carbohydrate: the most abundant (51%) size fraction being dissolved carbohydrates &lt; 8 kDa in size, with dissolved EPS contributing 7% to total carbohydrate. Carbohydrate fractions differed in monosaccharide profiles; dissolved components being glucose rich; particulate EPS containing more mannose, xylose, fucose and arabinose. These profiles corresponded to those of cultured sea‐ice diatoms. Microbial abundance, silicate, nitrate and phosphate concentration and ice thickness were important environmental drivers, with thicker ice containing relatively more particulate EPS, with thinner ice containing high amounts of glucose‐rich smaller‐sized carbohydrate moieties. Changes in ice characteristics will alter the relative balance of labile and refractory carbohydrates generated within bottom ice layers, with implications for food webs and carbon turnover in the warming Arctic Ocean.</jats:p>