Minze Stuiver

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

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.

The preindustrial atmospheric14CO2 latitudinal gradient as related to exchanges among atmospheric, oceanic, and terrestrial reservoirs

A three-dimensional global tracer transport model (derived from a general circulation model) simulates geographic variations in atmospheric Δ14C in response to oceanic boundary conditions. Regional atmosphere-ocean 14CO2 fluxes are controlled by regional wind-dependent gas exchange coefficients (E), air-sea pCO2 differences (ΔpCO2) and oceanic 14C/12C deficiencies. We find that various preindustrial oceanic scenarios reconstructed from reasonable sets of such air-sea variables all produce model latitudinal gradients in atmospheric Δ14CO2 (the “NS Δ14C”) significantly greater than the measured preindustrial NS Δ14C of +4.4 ± 0.5‰ (45°N to 45°S), as estimated from pre-twentieth century tree rings. The NS Δ14C is insensitive to regional ΔpCO2 but is strongly contingent on the chosen values for surface ocean Δ14C and E of southern high latitudes (>50°S). The simultaneous seasonality in sea ice extent and high-latitude wind speeds may in part explain the discrepancy between modeled and measured preindustrial NS Δ14C. Terrestrial 14C sinks with longer turnover times (such as peatlands) also potentially may help to reduce the NS Δ14C. With our best estimates for preindustrial surface ocean Δ14C, ΔpCO2, and E values for other regions, we find a “best fit” ocean scenario in which the preindustrial southern surface ocean Δ14C is −95 ± 10 ‰, its ΔpCO2 is 0 ± 20 ppmv, and its E is 0.088 ± 0.010 M m−2 yr−1 μatm−1 (about 20% reduced from the widely accepted value of 0.110). An independent estimate of +6.5 ± 0.5 kg yr−1 for the net preindustrial oceanic 14C uptake is an important constraint on global mean and Antarctic E.

GISP2 Oxygen Isotope Data

Measured at University of Washingtons Quaternary Isotope Laboratory. Timescale (down to 2808 m) includes revisions by Meese as of Sept 1994. Depths below 167 m are D core; above 167 meters depths are B core+1.09 meters. Depth is top of interval.