Distribution and composition of dissolved amino acids in seawater at the Yap Trench

The distributions and compositions of total hydrolyzed amino acids ( THAA) , dissolved combined amino acids ( DCAA) and dissolved free amino acids ( DFAA) were investigated after analyzing seawater samples collected from different depths by CTD and from the sediment-seawater interface by the Jiaolong submersible, at 4 stations located in the Yap Trench in June, 2016. The results showed that the average concentration of THAA was (2.44±0.85) μmol /L, while the average concentrations of DCAA and DFAA were (1.97±0.82) μmol /L and (0.47±0.34)μmol /L, respectively.The concentrations of THAA and DCAA displayed a decreasing trend from surface layer to deep layer. In the vertical distribution, the concentrations of THAA varied differently in superficial layer (above 1000 meters). THAA, DFAA and DCAA had a similar concentrations below 1000 meter depth. In the study area, major constituents of dissolved amino acids were methionine, threonine , histidine, glutamic acid , valine and glycine. At the Yap Trench, neutral dissolved amino acids were dominant in total dissolved amino acids. The trend of vertical distributions of various types of THAA, DFAA, and DCAA were similar with the total THAA, DFAA, and DCAA. In sediment-seawater interface, the seawater in the northwest of the trench has high concentrations of THAA and DCAA, while the concentrations of DFAA were similar in the seawater at the sediment-seawater interface.