Confirmation of the Suess wiggles: 3200–3700 BC

Abstract

USING dendrochronologically dated tree rings de Vries1 showed that the atmospheric 14C concentration has not been entirely constant during the past few hundred years. By extending the North American bristlecone pine tree-ring chronology2 to nearly 8,000 yr ago, several radiocarbon laboratories succeeded in measuring deviations in the 14C concentration from the mid-nineteenth century natural 14C level to a maximum of about 10% around 4000 BC (refs 3–7). Superimposed on this general trend, Suess drew with ‘cosmic schwung’, medium-term variations through his data. These so-called ‘wiggles’ should correspond with variations in the abundance of radiocarbon in atmospheric carbon dioxide on a time scale between one decade and a few centuries. The resulting irregular shape of Suess' calibration curve has been questioned during the past few years8,9. The overall result, however, is that no generally accepted 14C calibration curve is yet available. It would be most convenient to measure 14C concentrations in single tree rings with much higher precision than the usual 4–6‰. For this, however, much larger samples are required than are available from the bristlecone pine tree. An excellent opportunity was presented by the sub-fossil oak trunks discovered in the river valley sediments of southern Germany9; our measurements of these trunks are reported here.