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

Abstract

The Arctic region is undeniably changing, with significant losses in sea ice cover and changing riverine inputs to the Arctic Ocean (Peterson et al., 2006). A record low sea ice extent was reported in September 2012 (D. Perovich et al., 2012) and the summer sea ice has not exceeded or returned to pre-2007 levels yet (Perovich et al., 2019). The rapid reduction of Arctic summer sea ice causes an increase in the amount of light penetrating into the ocean (Nicolaus et al., 2012), enhancing sea-ice melt (Markus et al., 2009) and affecting the aquatic ecosystems (Arrigo & van Dijken, 2015; Arrigo et al., 2012). Arrigo and van Dijken (2015) showed that the 30% increase in the annual net primary production in the Arctic Ocean between 1998 and 2012 was associated with reduced sea ice. Planktonic dissolved organic matter (DOM) is considered as a major source of marine DOM (Osburn et al., 2019). The increase in the primary production of the Arctic Ocean (Arrigo et al., 2008) could contribute to increased production of autochthonous DOM in polar waters (Shen et al., 2018). Optical properties including absorbing and fluorescing properties have been used to assess DOM composition and fate (Coble, 2007; Nelson & Gauglitz, 2016), and trace water masses in Arctic waters (Dainard Abstract 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. Plain Language Summary The Arctic Ocean is a hostile environment undergoing rapid changes. However, it is not clear how the fast decline in sea cover and the increase in freshwater content in the Beauf...

Spatial Distribution of Colored Dissolved Organic Matter in the Western Arctic Ocean

“…Rather, CDOM variations may be related to internal production by a microbial carbon pump that is more active in the basin area than on the shelf. Microbial-origin CDOM fluorescent components are abundant in basin water [19], with previous studies having found a significant increase in levels of the smallest phytoplankton (picophytoplankton) in the basin area in response to environmental changes [39,40].…”

“…Previous report also found that the subsurface layer of basin area has distinctive enriched terrestrial humic EEM signatures [19]. Fluorescent components C3 and C4 can thus trace the distribution of Pacific water in the western Arctic Ocean.…”

“…Such changes in physical and biogeochemical processes (e.g., expansion of Pacific water inflow, terrestrial input, and microbial degradation) are likely to alter the biogeographic distribution of CDOM. Previous reports have indicated the considerable temporospatial variability of CDOM concentrations in response to changes in hydrographic and sea-ice conditions [18,19], which influence phytoplankton bloom [18] and photodegradation of humic material [19]. The bioavailability of DOM, which supports microbial food webs, also exhibits considerable pan-Arctic variability, with high labile DOM observed in productive shelves (e.g., Chukchi and Barents Seas) and low labile DOM in oligotrophic shelves (e.g., Beaufort and East Siberian Seas) [20].…”

Spatial Distributions of Riverine and Marine Dissolved Organic Carbon in the Western Arctic Ocean: Results From the 2018 Korean Expedition

“…Although bulk DOC concentration provides quantitative information regarding DOC production (or input) and consumption (or loss), previous studies have shown that the seasonal production of bioavailable marine DOC via primary production as well as the influence of riverine DOC is not apparently reflected in bulk DOC distribution in the western Arctic Ocean (e.g., the Chukchi and Beaufort Seas) (e.g., Davis & Benner, 2005; DeFrancesco & Guéguen, 2021; Jung, Son, et al., 2021; Mathis et al., 2007; Shen et al., 2012). For example, Davis and Benner (2005) reported that concentrations of bulk DOC did not exhibit a significant seasonal change in surface water of the Canada Basin, but dissolved amino acids concentrations (indicators of bioavailable DOC) increased by 45% between spring and summer.…”

“…This is probably because the elevated production of marine DOC in summer is masked by the concurrently enhanced input of riverine DOC, making the changes in bulk DOC concentrations less discernible during productive seasons (Shen, Fichot, et al., 2016). Furthermore, DeFrancesco and Guéguen (2021) found no interannual variation in bulk DOC concentration in the polar mixed layer of the Canada Basin over an 11‐year period (2007–2017), although the composition of dissolved organic matter (DOM) showed pronounced changes over time. The aforementioned previous studies suggest that the seasonal variations in marine or riverine DOC are reflected in the composition of DOC but less in bulk DOC concentrations.…”