Temporal and spatial variations of particulate and dissolved amino acids in the East China Sea

Concentrations of amino acids in dissolved and particulate pools in the East China Sea (ECS) were determined during two cruises (October-November 2013 and May-June 2014). The spatial distributions of total hydrolyzed amino acids (THAA), dissolved combined amino acids (DCAA), dissolved free amino acids (DFAA), and particulate amino acids (PAA) in the study area were considerably influenced by phytoplankton biomass and circulations. In addition, in situ phytoplankton production and terrestrial input are the major sources of amino acids in the ECS. The %C-PAA and %N-PAA positively correlated with chlorophyll a (Chl-a), thus reflecting their phytoplankton sources. The concentrations of amino acids were higher in coastal waters than in open sea, revealing the effects of terrestrial input on amino acid concentrations. Moreover, the vertical distributions of THAA, DCAA, DFAA, and PAA exhibited similar patterns, i.e., decreasing trends from the surface water to the bottom water. Our study indicated that the deposition of phytoplankton biodetritus may affect the vertical distributions of amino acids. The major constituents of THAA were glycine, serine, and glutamic acid, whereas the major constituents of PAA are glycine, glutamic acid, and alanine. The diel variation of THAA presented a certain hysteresis, following the variation of Chl-a. Particle sorption had a contribution in describing the particulate pool and dissolved pool in the Changjiang River.