Alexei N. Peristykh

Secular variation of Delta C-14 during the Medieval Solar Maximum: A progress report

The Earth is within the Contemporaneous Solar Maximum (CSM), analogous to the Medieval Solar Maximum (MSM). If this analogy is valid, solar activity will continue to increase well into the 21st century. We have completed 75 single-ring and 10 double-ring measurements from AD 1065 to AD 1150 to obtain information about solar activity during this postulated analog to solar activity during the MSM. Delta (super 14) C decreases steadily during the period AD 1065 to AD 1150 but with cyclical oscillations around the decreasing trend. These oscillations can be successfully modeled by four cycles. These four frequencies are 1/52 yr (super -1) , 1/22 yr (super -1) , 1/11 yr (super -1) , and 1/5.5 yr, i.e., the 4th harmonic of the Suess cycle, the Hale and Schwabe cycles and the 2nd harmonic of the Schwabe cycle.

Solar cycle length and 20th Century northern hemisphere warming: Revisited

It has been suggested that the length of the solar cycle (SCL) is related to solar forcing of global climate change [Friis-Christensen and Lassen, 1991]. Although no physical mechanism had been proposed, the relation seemed to be supported by interesting correlations with several paleoclimate records and, separately, with the 20th century Northern Hemisphere instrumental record. Actually, what has been correlated is the quasi-sinusoidal Gleissberg cycle which is slightly greater in the 18th century than in the 20th century. Using the pre-industrial record as a boundary condition, the SCL-temperature correlation corresponds to an estimated 25% of global warming to 1980 and 15% to 1997.

Radiocarbon production by the gamma-ray component of supernova explosions

Supernova explosions occur at the rate of about two per century in a standard galaxy whose light is equal to 1010 Suns, assuming that the Hubble constant is 100 km-1 s per Mpc (Murdin 1990). In our galaxy, seven supernovas have been visually observed since the 2nd century AD. There are also two optical supernova remnants and one that is only a radio remnant, for a total of 10 in 18 centuries, or alittle more than one every other century (Table 1, Fig. 1). Supernovas are the source of not only visible, but also ultraviolet and infrared light, as well as neutrinos and cosmic rays. Cosmic rays include nuclides (ionized hydrogen and helium as well as heavier elements), X rays and y rays.

MODULATION OF ATMOSPHERIC 14C CONCENTRATION BY THE SOLAR WIND AND IRRADIANCE COMPONENTS OF THE HALE AND SCHWABE SOLAR CYCLES

14C abundance on the Earth can be modulated by both the solar wind and irradiance components of the solar cycle. The magnetic field component of the solar wind modulates 14C production whereas the irradiance component can result in a change in the exchange rate between the various reservoirs of the carbon biogeochemical cycle. The effects would be nearly synchronous and difficult to separate. The 0.1 % amplitude of irradiance variation during the two most recent solar cycles is well known. A 22-yr cycle exists also in the measured global temperature record.

Regional Radiocarbon Effect Due to Thawing of Frozen Earth

Accelerator mass spectrometry (AMS) measurement of 25 single-year tree rings from AD 1861-1885 at ca. ±3.5‰ precision shows no evidence of an anomalous 11-yr cycle of 14C near the Arctic Circle in the Mackenzie River area. However, the ∆14C measurements are lower on average by 2.7 ± 0.9 (v)‰ relative to 14C measurements on tree rings from the Pacific Northwest (Stuiver and Braziunas 1993). We attribute this depression of 14C to thawing of the ice and snow cover followed by melting of frozen earth that releases trapped 14C-depleted CO2 to the atmosphere during the short growing season from May through August. Correlation of ∆14C with May-August estimated temperatures yields a correlation index of r = 0.60. The reduction in ∆14C is dominated by seven years of anomalous depletion. These years are 1861, 1867-1869, 1879-1880 and 1883. The years 1867-1869 are coincident with a very strong ENSO event.

Solar and Climatic Implications of the Centennial and Millennial Periodicities in Atmospheric Δ14C Variations

Temporal changes in atmospheric 14 C require high precision calibration of the radiocarbon time scale. The calibration process also provides Δ 14 C which is the age and fractionated corrected deviation of past atmospheric 14 C relative to an international standard. The dominant cause of atmospheric 14 C fluctuation is changes in the geomagnetic dipole moment. Detrending yields residual Δ 14 C which can be related to solar activity and climate change. The biogeochemical cycle of 14 C acts as a lowpass filter that greatly attenuates the high frequency components of solar activity. This attenuation is compensated by higher production rate and higher measurement precision relative to other cosmogenic isotopes. The spectrum of Δ 14 C contains many periods, overtones and combination tones. We are concerned here with the millennial and centennial periods. The Suess cycle (208 yr) and Gleissberg (88 yr) are discrete solar cycles that can be related to forcing of climate change whereas the millennial cycles do not appear to have an independent existence but are required by Fourier analysis to reconstruct the variance of the century scale cycles. We find the most effective way of demonstrating the relationship between residual Δ 14 C and climate is to match the pattern of residual Δ 14 C with the pattern of climate change.