Characteristics of dissolved sugars in the Southern Yap Trench from sea surface to hadal zone

2,4,6-Tripyridine-s-triazine (TPTZ) spectrophotometric method was applied to determine the concentrations of dissolved monosaccharides (MCHO), polysaccharides (PCHO), and total carbohydrate (TCHO) in seawater samples collected from sea surface to hadal zone and sediment-seawater interface of the Southern Yap Trench in the Western Pacific Ocean. Results show that the concentrations of MCHO, PCHO, and TCHO ranged from 6.3 to 22.3 mu mol C/L, 1.1 to 25.4 mu mol C/L, and 12.1 to 44.9 mu mol C/L, respectively, from the euphotic layer to the hadal zone of the trench. At different sampling stations, the concentrations of MCHO, PCHO, and TCHO in the seawater showed complex vertical variation characteristics, but the overall variation trends were decreasing with water depth. In the Southern Yap Trench, the maximum concentration of MCHO in the seawater appeared in the euphotic layer, and the minimum in the hadal zone. The maximum concentration of PCHO appeared in the euphotic layer, and the minimum in the bathypelagic layer. The water layer where the maxima and minima of the average concentration of TCHO appeared was consistent with that of PCHO. PCHO was the major component of TCHO in the seawater of the Southern Yap Trench. In the seawater from the sediment-seawater interface, the concentrations of MCHO, PCHO, and TCHO ranged from 8.4 to 10.6 mu mol C/L, 3.8 to 5.8 mu mol C/L, and 12.2 to 15.2 mu mol C/L, respectively, and MCHO was the major component of TCHO. The key factors affecting the concentration and existing forms of dissolved sugars in the seawater of the Southern Yap Trench included photosynthesis, respiration, polysaccharide hydrolysis, adsorption and desorption of particulate matter, trench "funnel effect", deep ocean currents, sediment resuspension, and etc. This study provided fundamental data about labile organic matter in abyss and hadal zone of marine environment, which is significant for further understanding of deep-sea organic carbon cycle.