Long-term Trends in Dissolved Organic Matter Composition and Its Relation to Sea Ice in the Canada Basin, Arctic Ocean (2007-2017)

Absorbance and fluorescence properties of dissolved organic matter (DOM) were measured in the upper and lower polar mixed layer (UPML and LPML, respectively) over an 11-year period (2007-2017) to assess for yearly changes in the quality and quantity of colored and fluorescent DOM (CDOM and FDOM, respectively) in relation with sea ice concentration in central Canada Basin waters. The LPML waters were enriched in CDOM, total dissolved lignin phenols, terrestrial humic-like C1, and in microbial humic-like C2 and C7 relative to the UPML waters (p > 0.05). The low ice years (i.e., 2012, 2016-2017) were characterized by lower humic-like fluorescence intensity (C4 only) and abundances relative to high ice years (i.e., 2007-2011, 2013-2015), likely the result of the preferential photoalteration of humic material when sea ice concentration was reduced. Significant time increases were found in tryptophan-like C3 in UPML and terrestrially derived humic-like C4 in LPML, suggesting an increase in the proteinaceous and terrigenous character of FDOM in UPML and LPML during the 11-year period, respectively. No interannual variation in dissolved organic carbon concentration was found in LPML and UPML. Weak but positive Spearman correlations were found between the humic-like intensities and abundances, and sea ice concentration in UPML waters, a consequence of reduced photodegradation in ice covered waters. This 11-year survey provides the first insight into the influence of summer sea ice concentration and river runoff on the quality and quantity of CDOM and FDOM.