Abstract
Amino acids dissolved in sea water either in free or combined forms were determined in the wide area of the western North Pacific by means of a fluorometric method of o-phthalaldehyde-amino acids adduct. The concentration of the total amino acids ranged from 44 to 213 μg l-1 and it is found that the concentration in water to the north of the Kuroshio front shows a slightly lower value than that of the south side. The ratio of free to the total amino acids is less than 0.2. In general, the concentration of amino acids was high in the surface and decreased to a nearly constant value in the intermediate and deep water. The molecular size distribution of amino acids revealed that about 60% of amino acids is involved in organic matters with molecular weight ranging from 1.5×103 to 5×104. About 10% of amino acids is involved in organic matters with molecular weight of 15×104. The composition of amino acids indicates that a major group of amino acids is involved in neutral aliphatic amino acids. Among the total amino acids, 40 to 80% is adsorbed on XAD-2 resin and a major fraction is involved in organic matters with molecular weight ranging from 5×103 to 2×104, in which most of the metal organic compounds are included. The composition of individual amino acids adsorbed on the XAD-2 resin is a little different from that of original sea water.
