An organic carbon isotopic record of glacial-postglacial change in atmospheric pCO2 in the sediments of Lake Biwa, Japan

Abstract

A 12 m piston core of sediment from Lake Biwa, Japan, provides a high-resolution record of sedimentary organic matter accumulation over the Pleistocene-Holocene transition. Organic carbon concentrations are generally 1-2% in sediments deposited since 15 kyr ago. C/N ratios indicate that the organic matter is predominantly from aquatic production. A shift in organic carbon isotopic composition from -21[per mille sign] to -25[per mille sign] occurs over the glacial-postglacial boundary. Changes in lake productivity, organic matter preservation, sources of organic matter, and water temperature can be eliminated as probable causes of the observed organic carbon isotopic shift. Annual overturn of lake waters and rapid dissolution of biogenic carbonates maintain equilibrium between atmospheric CO2 and dissolved CO2 in this lake. The isotopic composition of organic matter buried in the sediments of Lake Biwa consequently appears to record the shift in atmospheric pCO2 from 200 ppm to 280 ppm which occurred at the Pleistocene-Holocene transition.