Composition and distribution of dissolved carbohydrates in the Beaufort Sea Mackenzie margin (Arctic Ocean)

• Dissolved organic carbon (DOC) and dissolved carbohydrate (TDCHO) patterns in the Beaufort Sea Mackenzie margin
• TDCHO to DOC ratios and freshness of carbohydrates
• Sources and cycling of dissolved carbohydrates in the Beaufort Sea Mackenzie margin

The carbohydrate 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 the 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 carbohydrates 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 and 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 the shelf and basin stations, respectively. Semi-labile DOC estimated values accounted for 10–40% and 20–50% of DOC in the slope and basin areas and agreed well with the above TDCHO/DOC values suggesting a gradient of carbohydrate freshness 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.