ABSTRACT

The carbon isotope ratios of bog peat in the Ozegahara peatland, Japan, were measured. The vertical variation of the bulk peat featured: 1) rapid decrease of the carbon isotope ratio (δ¹³C) near the surface, 2) broad rises in the ratio around depths corresponding to 3000, 5500, 7500 years BP with a period of approximately 2500 years, and 3) a further decrease toward the bottom. In order to understand the reasons for the changes, peat components were separated and their isotopic composition measured along with modern peat-forming vegetation. The selective decay of holocellulose is responsible for the rapid decrease of δ¹³C in the surface layers, and the transition from earlier vegetation caused the further decrease of δ¹³C near the bottom. The decay constant for holocellulose was estimated to be as small as 0.001 yr^–1. The variation of δ¹³C seemed to be synchronized with sea level change, but showed poor correlation with solar activity and the temperature change estimated from pollen analysis. The δ¹³C of peat mosses lacking in stomata would increase with the rise in atmospheric CO₂. The increase in the atmospheric CO₂ occurring synchronously with sea level rise could be the reason for the periodical change. Some climatic information of the Holocene period may have been recorded in the Ozegahara bog peat.