Anthropogenic and solar components of hemispheric ¹⁴C

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.