Anthropogenic and solar components of hemispheric 14C

Abstract

A variable solar (helio-magnetic) modulation of the cosmic ray flux causes atmospheric 14C to change on a decadal to century timescale. Ocean-atmosphere exchange rates and atmospheric circulation patterns play a role in Northern-Southern Hemispheric 14C offsets and regional 14C differences that are significant for radiocarbon dating. Time dependent radiocarbon age differences, relative to Washington, were determined for Alaska (A.D. 1884 - 1932), South Chile (A.D. 1850 - 1952 and A.D. 1670 - 1722), Tasmania (A.D. 1895 - 1950) and Siberia (A.D. 1545 - 1715). Twentieth century fossil fuel CO2, lacking 14C and mostly released in the Northern Hemisphere (N), has entered the Southern Hemisphere (S) by atmospheric N-S exchange. Regional 14C time series show that initial (19th century) positive N-S 14C offsets switch to negative values by AD 1940. First order carbon reservoir modeling predicts such crossovers.