|Composition and distribution of dissolved carbohydrates in the Beaufort Sea Mackenzie Margin (Arctic Ocean) |
(Article) Publié: Marine Chemistry, vol. 166 p.92–102 (2014)
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The sugar composition (TDCHO) of dissolved organic matter (DOM) was studied in the Mackenzie margin (Southeast Beaufort Sea) in summer 2009 as a part of the MALINA project. Sampling was performed in shelf (bottom depth ≤100 m), slope (100 m < bottom depth ≤1000 m), and basin (bottom depth > 1000 m) areas of the Mackenzie margin. Our results showed that sugar concentrations did not follow dissolved organic carbon (DOC) patterns, which decreased from shelf to basin stations (from 115 to 65 µM), but instead remained rather constant (965-900 nM), indicating an accumulation of sugars in surface waters (0-80 m). TDCHO concentrations exhibited their highest values (> 1000 nM) and higher relative abundance to DOC in the central sector of the studied area, especially in the zone between 130-135°W indicating differences in their distribution in the broader area and possible various sources. TDCHO represented 6 ± 2% and 8 ± 3% of DOC (TDCHO-C/DOC) for shelf and basin stations, respectively. Based on values of bacterial carbon demand and glucosidase activities, it was estimated that ~4% of DOC was available as carbohydrate for bacterial utilization within the basin area, whereas the value drops to <0.5% of DOC in the shelf area. These results agree well with the above TDCHO/DOC values suggesting a gradient of carbohydrate lability from inshore to offshore stations. The high Fucose + Rhamnose relative abundances (Fuc. + Rha. 15-18%) and high C/N ratios (19-13) recorded in the surface waters of the shelf area are indicative of soil-derived matter delivered by the Mackenzie River, possibly with contributions from mainly gymnosperm terrestrial plants. The high abundance of glucose (up to 50%) suggests that the carbohydrate component of the DOM in the Mackenzie margin appears to have a more pronounced marine autochthonous origin with an important contribution of terrestrial sources, especially for the shelf stations. Overall, these results suggest a largely uniform distribution of TDCHO carbohydrates within the area with occasional patches of lower concentrations.