Climatic, Solar, Oceanic, and Geomagnetic Influences on Late-Glacial and Holocene Atmospheric 14C/12C Change

Abstract

Late-glacial and Holocene 14 C/12 C ratios of atmospheric CO 2 vary in magnitude from a few per mil for annual/decadal pertubations to more than 10% for events lasting millennia. A data set illuminating 10- to 10 4-yr variability refines our understanding of oceanic (climatic) versus geomagnetic or solar forcing of atmospheric 14 C/12 C ratios. Most of the variance in the Holocene atmospheric 14 C/12 C record can be attributed to the geomagnetic (millennia time scale) and solar (century time scale) influence on the flux of primary cosmic rays entering the atmosphere. Attributing the observed atmospheric 14 C/12 C changes to climate alone leads to ocean circulation and/or global wind speed changes incompatible with proxy records. Climate-(ocean-)related 14 C redistribution between carbon reservoirs, while evidently playing a minor role during the Holocene, may have perturbed atmospheric 14 C/12 C ratios measurably during the late-glacial Younger Dryas event. First-order corrections to the radiocarbon time scale (12,000–30,000 14 C yr B.P.) are calculated from adjusted lake-sediment and tree-ring records and from geomagnetically defined model 14 C histories. Paleosunspot numbers (100–9700 cal yr B.P.) are derived from the relationship of model 14 C production rates to sunspot observations. The spectral interpretation of the 14 C/12 C atmospheric record favors higher than average solar activity levels for the next century. Minimal evidence was found for a sun-weather relationship.