Sun, ocean, climate and atmospheric 14CO2 : an evaluation of causal and spectral relationships

Abstract

Solar (heliomagnetic), geomagnetic and oceanic forcing all play a role in atmospheric ¹⁴CO₂ change. Here we assign the variance associated with certain periodicities in a single year (0-450 cal. BP) and a Holocene bidecadal (0-11400 cal. BP) ¹⁴CO₂ record to specific forcing factors. In the single-year time series the variance in the 2-6-year periodicity range is attributable to El Niño-Southern Oscillation (ENSO) ocean perturbations. A 10-11-year component is partially tied to solar modulation of the cosmic ray flux, and multidecadal variability may relate to either solar modulation or instability of the North Atlantic thermohaline circulation. For the early Holocene bidecadal ¹⁴C record we derive a 512-year atmospheric ¹⁴C periodicity which relates to instabilities in North Atlantic thermohaline circulation. North Atlantic deep water formation increased near the start, instead of the termination, of the Younger Dryas interval. The ubiquitous 206-year ¹⁴C cycle is assigned either to solar modulation, or to solar modulation modified by a climate (ocean) response. The latter modification is discussed as part of a hypothetical mechanism explaining postulated climate-14C relationships in which a minor solar- induced Maunder Minimum climate change is amplified by salinity effects on North Atlantic thermoha line circulation.