Atmospheric P CO2 changes recorded in lake sediments

Abstract

Recent studies of polar ice cores indicate that there have been appreciable secular variations1–4 in atmospheric CO2 concentrations during the past 40,000 yr. We have now theoretically examined the expected steady state changes in atmospheric Δ14C (a measure of the 14C/12C ratio) for different sizes of the atmospheric CO2 reservoir, keeping fixed the rate of production of 14C as well as the global carbon cycle exchange parameters. These calculations show that atmospheric Δ14C is highly sensitive to changes in total atmospheric CO2. Appreciable changes in Δ14C can also result from changes in the large-scale ocean circulation5–7. Thus, the interpretation of the atmospheric Δ14C palaeorecord requires supplementary geophysical evidence such as changes in sea level and in the carbonate chemistry of the oceans. We discuss the available data on past atmospheric Δ14C with regard to changes in global carbon cycle parameters and in the rate of production of 14C due to changes in Earth's dipole magnetic field.