The distribution of amino acids in submarine sediments from the eastern part of the East China Sea

Abstract

Two muddy core samples and three carbonate surface samples from the eastern part of the East China Sea were examined for total concentration and composition of amino acids and amino sugars. The core samples, one 140 cm long and obtained from the basin (Danjo Basin, core No. 69-63), the other 110 cm long and taken from the continental shelf (China Continent, core No. 69-22), were divided into 10 cm lengths, and analyzed on an aminoacid analyzer. In the muddy core sediments, total amino-acid contents range from 0.339 to 2.92 mg g −1. However, the content in the basin sediments is 1.84–2.92 mg g −1, and that in the shelf sediments is 0.339–1.31 mg g −1. The ratios of basic amino acids to total amino acids are also higher in the basin. The vertical distribution of acidic amino acids changes irregularly in both the basin and continental shelf, the largest fluctuation being found in the continental shelf sediments. The ratios of non-protein amino acids to total amino avids are higher in the continental shelf. Corcerning the content of D-alloisoleucine and L-isoleucine, only trace amounts of D-alloisoleucine are found in the basin sediments, but high ratios of D-alloisoleucine to L-isoleucine are recognized in some muddy sediments (20, 60 and 100 cm deep) from the continental shelf, indicating the possibility that these are the relict sediments. The differences in concentration and composition of amino acids in the muddy sediments from the basin and continental shelf, are believed mainly due to the differences in the quantity of organic matter supply, composition of source materials, sedimentary environment and diagenetic changes. Moreover, the fluctuations in vertical distribution of total amino acids and the composition of amino acids may be caused by paleoenvironmental changes. In the carbonate sediments, the amino-acid composition is strikingly different from that in any of the muddy core sediments, namely, the carbonate sediments are characterized by a low content of basic amino acids, remarkably high concentration of acidic amino acids and trace amounts of non-protein amino acids. Aspartic acid is the most abundant constituent, amounting to ∼22.8–31.6% of the total amino acids. Such a predominant amino acid is not found in the muddy core sediments. The controlling factor which has influenced the difference in amino-acid composition between the two sediments seems to be the differences in the amino-acid composition of the source materials; for carbonate sediments the source materials are skeletal carbonate protein, whereas for muddy sediments they are plankton and soil organic materials. Two of the three carbonate sediments have high ratios of D-alloisoleucine to L-isoleucine, supporting the possibility that they are Pleistocene relict sediments.