The sharp rise of DELTA-14C ca. 800 cal BC: possible causes, related climatic connections and the impact on human environments

In this study we report on accelerator mass spectrometry (AMS) wiggle-match dating of selected macrofossils from organic deposits ca. 800 cal BC (ca. 2650 BP). Based on paleological, archaeological and geological evidence, we found that the sharp rise of atmospheric 14C between 850 and 760 cal BC corresponds to the following related phenomena: 1. In European raised bog deposits, the changing spectrum of peat forming mosses and a sharp decline in decomposition of the peat indicate a sudden change from relatively dry and warm to cool, moist climatic conditions. 2. As a consequence of climate change, there was a fast and considerable rise of the groundwater table so that peat growth started in areas that were already marginal from a hydrological point of view. 3. The rise of the groundwater table in low-lying areas of the Netherlands resulted in the abandonment of settlement sites. 4. The contemporaneous earliest human colonization of newly emerged salt marshes in the northern Netherlands (after loss of cultivated land) may have been related to thermal contraction of ocean water, causing a temporary stagnation in the relative sea-level rise. Furthermore, there is evidence for synchronous climatic change in Europe and on other continents (climatic teleconnections on both hemispheres) ca. 2650 BP. We discuss reduced solar activity and the related increase of cosmic rays as a cause for the observed climatological phenomena and the contemporaneous rise in the 14C-content of the atmosphere. Cosmic rays may have been a factor in the formation of clouds and precipitation, and in that way changes in solar wind were amplified and the effects induced abrupt climate change