南極産二枚貝Laternula ellipticaの殻に残された安定同位体の記録 : 南極の融氷水の歴史

• Main Authors: 河合 庸展, 和田 秀樹
• Format: Report
• Language: Japanese
• Published: 静岡大学地球科学教室 1999
• Subjects: oxygen isotope; carbon isotope; Antarctica; Laternula elliptica; melt water history; 450; Antarctic; Antarc*; Ice Sheet
• Online Access: http://hdl.handle.net/10297/358; https://shizuoka.repo.nii.ac.jp/?action=repository_uri&item_id=429

Stable isotopes of oxygen and carbon are useful tools in understanding the paleoclimates. The stereome isotopic data of an organism is indicative of the isotopic composition of the ocean water where the organism lived. In this study we measured stable carbon and oxygen isotopes of the shell an Antarctic Bivalvia Laternula elliptica. Samples of fossil Antarctic Bivalvia L. elliptica shell from the Pliestocene (46ka) and Holocene (3.5 ka-4ka) were collected from Lutzow Holm Bay and from the Recent L. elliptica at MucMurdo Sound in Antarctica. The quantity of meltwater from ice sheet militating the ocean water can be estimated from the δ^<l8>O of shells of Laternula. Detailed microsampling within a shell also sheds light on seasonal isotopic variation. We measured two modern as well as three fossil shells (3.5ka-4ka) and some 46ka shell fragments. The δ^<l3>C values suggest that in L. elliptica inception of carbon occurred during the course of growth. The δ^<l8>O values have a seasonal variation of about 1‰. The light values are suggestive of addition of meltwater indicating summer season and the heavy values are likely to winter. This seasonality gives important information about the life span of a molluscan shell. Using these data the life span of the Recent L. elliptica might have been for 7 years and that of the fossil Laternula about 9 years. The δ^<l8>O fluctuation within Recent shells are in the range of 1‰, and that of the fossil shells in 3‰, which shows that there was a greater variation of oxygen isotopes during the course of life 3.5ka-4ka than the Recent. The ^<l8>O depleted value suggests that there was mass mixing of meltwater with the sea water at 3.5ka-4ka which decreased toward the Recent. In this study the shell data of the three periods indicate that the biggest meltwater effect was the highest recorded at 3.5ka-4ka and the second was around 46ka. publisher