A reconstruction of radiocarbon production and total solar irradiance from the Holocene <sup>14</sup>C and CO<sub>2</sub> records: implications of data and model uncertainties

Abstract

Abstract. Radiocarbon production, solar activity, total solar irradiance (TSI) and solar-induced climate change are reconstructed for the Holocene (10 to 0 kyr BP), and TSI is predicted for the next centuries. The IntCal09/SHCal04 radiocarbon and ice core CO2 records, reconstructions of the geomagnetic dipole, and instrumental data of solar activity are applied in the Bern3D-LPJ, a fully featured Earth system model of intermediate complexity including a 3-D dynamic ocean, ocean sediments, and a dynamic vegetation model, and in formulations linking radiocarbon production, the solar modulation potential, and TSI. Uncertainties are assessed using Monte Carlo simulations and bounding scenarios. Transient climate simulations span the past 21 thousand years, thereby considering the time lags and uncertainties associated with the last glacial termination. Our carbon-cycle-based modern estimate of radiocarbon production of 1.7 atoms cm−2 s−1 is lower than previously reported for the cosmogenic nuclide production model by Masarik and Beer (2009) and is more in-line with Kovaltsov et al. (2012). In contrast to earlier studies, periods of high solar activity were quite common not only in recent millennia, but throughout the Holocene. Notable deviations compared to earlier reconstructions are also found on decadal to centennial timescales. We show that earlier Holocene reconstructions, not accounting for the interhemispheric gradients in radiocarbon, are biased low. Solar activity is during 28% of the time higher than the modern average (650 MeV), but the absolute values remain weakly constrained due to uncertainties in the normalisation of the solar modulation to instrumental data. A recently published solar activity–TSI relationship yields small changes in Holocene TSI of the order of 1 W m−2 with a Maunder Minimum irradiance reduction of 0.85 ± 0.16 W m−2. Related solar-induced variations in global mean surface air temperature are simulated to be within 0.1 K. Autoregressive modelling suggests a declining trend of solar activity in the 21st century towards average Holocene conditions.

The impact of geomagnetic spikes on the production rates of cosmogenic 14C and 10Be in the Earth's atmosphere

“…Both spikes drive a decrease in 14 C production rate, which is due to the concomitant increase in the dipole field moment (Figure 2b). Model M13 gives a practically negligible decrease, well within the uncertainties of ±(0.05-0.08) at/cm 2 /s estimated by Roth and Joos [2013]. For the M65 model, the spike-related decrease is about 0.1 at/cm 2 /s (∼ 6%).…”

“…The impact on Q ( 14 C ) is modeled to be about 6% of the mean production rate over the period of concern [Roth and Joos, 2013]; the impact is even stronger (about 10%) on D ( 10 Be )…”

“…are then compared with the 14 C production rates reconstructed by Roth and Joos [2013] from the tree-ring-based measurements of INTCAL-2009[Reimer et al, 2009. In order to model data of 10 Be measured in polar ice, the 10 Be production is computed using the model of Kovaltsov and Usoskin [2010].…”

Level and length of cyclic solar activity during the Maunder minimum as deduced from the active-day statistics

“…On the other hand, estimates of the cycle length based on cosmogenic 14 C data suggest much longer cycles during Grand minima (13−16 years). We note, however, that 14 C data cannot resolve individual cycles, because of the global carbon cycle attenuating high-frequency variability (Roth & Joos 2013), but instead yields the mean periodicity over the interval analysed (e.g. Miyahara et al 2004).…”

Implications of potential future grand solar minimum for ozone layer and climate

“…The reconstructions reveal cycles in the order of hundreds of years, called "grand solar minima" and "grand solar maxima". Several recent publications suggest a new grand solar minimum to 30 occur in the 21 st century (Abreu et al, 2010;Lockwood et al, 2011;Roth and Joos, 2013) and to last even until the end of 22 nd century . Such events might have a significant impact on climate and on the ozone layer.…”