貝殻化石中アスパラギン酸のラセミ化から推定する古環境温度

概要

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Temperature-dependent ammo acid racemization reaction has been utilized to estimate paleotemperatures for three fossil shells excavated at Hokkaido, Aichi, and Okinawa. The radiocarbon ages of these samples were determined to 5,700±100 B.P., 5,100±20 B.P., 26,860±1860 B.P., respectively. After complete removal of the contaminants of the shells, they were heated to proceed racemization based on simulation in a temperature range of 90-190℃ and for a time period of 4-600 hours. The heat-treated shells were dissolved in dilute HCl and then dialyzed in water to remove free amino acids and low molecular-weight peptides. The protein fraction was hydrolyzed into free amino acids with subsequent analysis of the D, L ratios of aspartic acid by HPLC. From the Arrhenius plots, the three samples have been estimated the average temperature to be 8.5℃ at Hokkaido, 14.6℃ at Nagoya, and 11.5℃ at Okinawa, respectively. Average temperatures obtained from Hokkaido and Nagoya have been considered to be reasonable, however, the sample from Okinawa has shown the average temperature unexpectedly low. The low average temperature of the Okinawa sample has been considered to be involved in the glacial and chilliness periods in its burial progress.
大阪府立工業高等専門学校の論文