ABSTRACT

Core samples of sediments at depths of 0-300 cm at Rikubetsu, Hokkaido, Japan were analyzed for total organic carbon (TOC) concentration, total hydrolyzed amino acids (THAA) and density of viable microorganisms. TOC, THAA and density of viable microorganisms were greatest at the surface and decreased with the depth: THAA showed 62 μmol/g at a depth of 0-5 cm. The correlation coefficients (r) for TOC and THAA versus cell density were 0.97 and 0.98, respectively. The alteration of dicarboxylic amino acids, aspartic acid and glutamic acid, to β-alanine and γ-aminobutyric acid respectively, via specific decarboxylation due to diagenesis were observed. Rate constant of aspartic acid racemization, k_ASP was determined to be 3.8 × 10^-5 at 4, 420 yrBP and 2.6 × 10^-5 at 9, 290 yrBP. Some anomalies in vertical distribution of THAA and cell density in the core sediment may indicate the presence of the past warmer period called “Hypsithermal” in Rikubetsu, Hokkaido, Japan.