Solar Modulation Effects in Terrestrial Production of Carbon-14

Abstract

ABSTRACT. This paper is concerned with the expected deviations in the production rate of natural 14C on the earth due to changes in solar activity. We review the published estimates of the global production rates of 14C due to galactic and solar cosmic ray particles, and present new estimates of the expected secular variations in 14C production, taking into account the latest information available on galactic cosmic ray modulation and long-term variations in solar activity.Estimated secular variations are related to data on atmospheric 14Cf 12C ratios based on tree rings. It is concluded that the observed higher frequency wiggles in atmospheric "C/12C ratios occurring with time scales of about two hundred years and of 1 to 2 percent in magnitude (de Vries, 1958; Suess, 1970a,b;1979;Damon, Lerman, and Long, 1978), are largely due to solar activity dependent modulation of the galactic cosmic ray flux by solar plasma. These variations override a slowly varying sinusoidal change of about 10 percent in magnitude during the last approximately 8000 years, which is believed to be primarily due to changes in the geomagnetic field. The high frequency modulation effect in 14C production is substantial, about 20 percent, which, considering the response function of the atmosphere (cf Houtermans, Suess, and Oeschger, 1973), is adequate to explain the observed 14C wiggles (also named Suess wiggles or de Vries oscillations) if in the past, periods of large modulation effects and also periods of weak modulation persisted, ie, the sun remained both active and inactive over long periods of time, of the order of several decades to centuries. The pioneering investigations of Eddy (1976; 1977) of the ancient records of solar activity make it plausible that the 14C wiggles in the ancient 14C/12C ratios are primarily due to modulation of galactic cosmic ray flux by a varying sun. Thus, the 14C wiggles are good indicators of solar activity in the past.We also present revised estimates of the production rates of 14C on the earth due to solar flare accelerated cosmic rays and limits of direct accretion of 14C on the earth.

Large 14 C excursion in 5480 BC indicates an abnormal sun in the mid-Holocene

“…According to several studies, if the solar modulation parameter becomes zero, the 14 C production rate can increase to ∼3 atoms per square centimeter per second (19,25,26). Averages of the production data for the periods of 5476-5471 BC (6 y) and 5482-5471 BC (10 y) are 2.9 and 2.6 atoms per square centimeter per second, respectively.…”

A history of solar activity over millennia

“…Several models have been developed for this cascade, in particular its hadronic branch with emphasis on the generation of cosmogenic isotope production. The first models were simplified quasi-analytical (e.g., Lingenfelter 1963;O'Brien and Burke 1973) or semiempirical models (e.g., Castagnoli and Lal 1980). With the fast advance of computing facilities it became possible to exploit the best numerical method suitable for such problems-Monte-Carlo (e.g., Beer 1999, 2009;Webber and Higbie 2003;Webber et al 2007;Usoskin and Kovaltsov 2008b;Kovaltsov and Usoskin 2010;Kovaltsov et al 2012;Argento et al 2013).…”

Assessment of different sunspot number series using the cosmogenic isotope 44 Ti in meteorites

“…The spectrum of Galactic cosmic rays (GCR) near Earth can be described by the force-field parametrization using a single parameter, called the modulation potential (Gleeson & Axford 1968;Castagnoli & Lal 1980;Usoskin et al 2005), which depends on the level of solar magnetic activity. One of the main heliospheric parameters, affecting the modulation potential, φ, is the OSF.…”