CORRECTION OF IN SITU COSMOGENIC NUCLIDE PRODUCTION RATES FOR GEOMAGNETIC FIELD INTENSITY VARIATIONS DURING THE PAST 800,000 YEARS

Abstract

We present integrated relative production rates for cosmogenic nuclides in rock surfaces, which take into account reported variations of the geomagnetic field intensity during the past 800,000 yr. The calculations are based on the model simulating cosmic ray particle interactions with the Earth's atmosphere given by Masarik and Beer [''Simulation of particle fluxes and cosmogenic nuclide production in the Earth's atmosphere,'' J. Geophys. Res. 104(D10), 12099-12111, 1999]. Corrections are nearly independent on altitude between sea level and at least 5000 m. The correction factors are essentially identical for all stable and radioactive cosmogenic nuclides with half-lives longer than a few hundred thousand years. At the equator, integrated production rates for exposure ages between ~40,000 to 800,000 yr are 10 to 12% higher than the present-day values, whereas at latitudes >40°, geomagnetic field intensity variations have hardly influenced in situ cosmogenic nuclide production. Correction factors for in situ 14C production rates differ from those of longer-lived nuclides. They are always smaller than ~2% because the magnetic field intensity remained rather constant during the past ~10 kyr, when the major fraction of the 14C extant today was produced.