Insights Into Water Mass Origins in the Central Arctic Ocean From In‐Situ Dissolved Organic Matter Fluorescence

Abstract

The Arctic Ocean receives a large supply of dissolved organic matter (DOM) from its catchment and shelf sediments, which can be traced across much of the basin's upper waters. This signature can potentially be used as a tracer. On the shelf, the combination of river discharge and sea‐ice formation, modifies water densities and mixing considerably. These waters are a source of the halocline layer that covers much of the Arctic Ocean, but also contain elevated levels of DOM. Here we demonstrate how this can be used as a supplementary tracer and contribute to evaluating ocean circulation in the Arctic. A fraction of the organic compounds that DOM consists of fluoresce and can be measured using in‐situ fluorometers. When deployed on autonomous platforms these provide high temporal and spatial resolution measurements over long periods. The results of an analysis of data derived from several Ice Tethered Profilers (ITPs) offer a unique spatial coverage of the distribution of DOM in the surface 800 m below Arctic sea‐ice. Water mass analysis using temperature, salinity and DOM fluorescence, can clearly distinguish between the contribution of Siberian terrestrial DOM and marine DOM from the Chukchi shelf to the waters of the halocline. The findings offer a new approach to trace the distribution of Pacific waters and its export from the Arctic Ocean. Our results indicate the potential to extend the approach to separate freshwater contributions from, sea‐ice melt, riverine discharge and the Pacific Ocean.

Climate warming-driven changes in the flux of dissolved organic matter and its effects on bacterial communities in the Arctic Ocean: A review

“…The fluxes of DOM into the Arctic Ocean were estimated to be 23 ± 2 Tg C yr -1 and 155 ± 13 Tg C yr -1 by inflow from the Pacific Ocean and the North Atlantic, respectively (Monteith et al, 2007;Bif and Hansell, 2019;Vetrov and Romankevich, 2019). Meanwhile, the concentration of DOM from the Pacific was estimated to be ~70 µM (Anderson and Amon, 2015), which is dominated by allochthonous DOM with a strong aliphatic character with very low light absorptivity (Pugach et al, 2018) and FDOM (~0.017 RU) (Stedmon et al, 2021;Cai et al, 2022). The DOC concentration in Atlantic seawater input was reported to be approximately 60 µM (Borsheim and Drinkwater, 2014;, which is characterized by a relatively low abundance of chromophoric DOM (cDOM) (Paulsen et al, 2018) and FDOM (~0.01 RU) (Stedmon et al, 2021), suggesting a lower contribution from terrestrial DOM compared to the Pacific seawater.…”

“…Meanwhile, the concentration of DOM from the Pacific was estimated to be ~70 µM (Anderson and Amon, 2015), which is dominated by allochthonous DOM with a strong aliphatic character with very low light absorptivity (Pugach et al, 2018) and FDOM (~0.017 RU) (Stedmon et al, 2021;Cai et al, 2022). The DOC concentration in Atlantic seawater input was reported to be approximately 60 µM (Borsheim and Drinkwater, 2014;, which is characterized by a relatively low abundance of chromophoric DOM (cDOM) (Paulsen et al, 2018) and FDOM (~0.01 RU) (Stedmon et al, 2021), suggesting a lower contribution from terrestrial DOM compared to the Pacific seawater. The DOM from the surface waters of both the Atlantic and Pacific was found to be relatively bio-refractory, with only 10% of the bio-labile fraction in the total pool (Amon and Benner, 2003).…”

“…The chemical makeup of DOM in the Arctic sea water varies with changing dominant input sources (or different regions) with dissimilar compositions of different organic components (Table 1). In the central Arctic Ocean, carbohydrates (i.e., glucose) and five distinctive fluorescent components, including tryptophan-like, tyrosine-like, terrestrial humic-like and two humic-like components, were detected (Piontek et al, 2021;Williford et al, 2021), and intensity of in-situ DOM fluorescence (water depths <25 m) reached >0.030 RU (up to 0.089 RU) (Stedmon et al, 2021). The Canadian Basin surface waters were characterized by high percentage of autochthonous CDOM (a 375 = 0.21 m -1 ), and the surface waters of the Eurasian Basin (100 m depth) showed a riverine feature (a 375 = 0.41 m -1 ) (Rossel et al, 2020).…”

“…These environmental processes contain and generate high quantities of dissolved organic matter (DOM). Climate change-related repercussions have led these processes to become DOM generators, accumulating substantial volumes of DOM in the Arctic Ocean, particularly in surface water (Tanaka et al, 2016;Stedmon et al, 2021). The role of DOM in marine ecosystems, notably as a substrate for bacterial communities, is highly dependent on its concentration and composition, both of which are closely related to its sources (Carlson, 2014).…”

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

“…Fluorescent components C3 and C4 can thus trace the distribution of Pacific water in the western Arctic Ocean. Other studies also indicate the potential to use DOM fluorescence in distinguishing between freshwater contributions of melt water, river water, and Pacific inflow [47].…”