Carbon Isotopic Variation and the Paleoclimate of Sediments from Lake Biwa

Paleoclimatic features in central Japan based on the stable isotope compositions of Lake Biwa sediments and speleothems.

“…According to Kanari's estimation (1975) based on several pieces of data of 14C and fission-track ages, the deepest horizon of the cored column showed the age of 550 x 103 years B.P. One of the present writers previously reported the vertical variations of organic carbon contents and the 13C/12C ratios of the sediments and suggested that the 13C/12C ratios widely fluctuated through the cored column and the fluctuation is caused by cyclic paleoclimate changes (Nakai 1972(Nakai , 1975.…”

“…Experimental procedure. Sediment samples for 13C/12C analyses were taken at intervals of 5 m from the cored column of 200 m length and analyzed with respect to 13C/12C ratios as described by Nakai (1972). Stalactite and flowstone samples were collected from Otaki Cave, Gifu Prefecture, near Lake Biwa.…”

“…The CaCO3 samples were drilled out of the cross-section of stalactite and the vertical section of flowstone at every interval of 1 to 5 mm and analyzed for 180/160 ratios as reported by Epstein et al (1953) (Fig. 1) has been explained by changes of the kinetic isotope effect with temperature during the past photosynthetic process in the lake (Nakai 1972(Nakai ,1975 . A general feature of these results obtained so far seems to be a tendency toward larger 5130 values when organic carbon contents, amounts of organic residues, are larger.…”

Paleoenvironmental features of Lake Biwa deduced from carbon isotope compositions and organic C/N ratios of the upper 800-m sample of 1,400-m cored column.

“…For carbon isotope analyses, sedimentary organic carbon was converted to carbon dioxide by the procedure described by Nakai (1960 and1978) and then the CO2 was purified with a liquid N2-n. penthane trap to remove SO2 and water vapor. The purified CO2 was isotopically determined with a VARIAN MAT CH-7 dual collector mass spectrometer.…”

“…On the other hand, small o13C values having large organic C/N can be understood as a large contribution of land plants. Besides the difference in organic sources, the O 13C value changes with temperature dependence of the kinetic isotope effect during photosynthesis (Nakai, 1972) . In general, from this effect one can expect an unquestionable tendency toward larger 513C values of the product during warmer periods resulting in a high lake-water level.…”