No abstract

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.

C-14 datings can not only provide us with estimates of the absolute age of objects or occupation layers, but also, when available in sufficient numbers, with initial and terminal datings for cultural phases, thus defining their duration. The value of this is obvious: differential duration in different areas can at last provide definitive answers to long-disputed questions concerning the direction of cultural movement.Working with large numbers of C-14 dates is, however, not entirely free of problems. We are, for example, regularly confronted with larger differences between datings expected to be of similar age than can be accounted for by mere statistical error (Vogel, 1969a) or which can be explained by contamination or other simple causes. One can stop at this point and accept a limited testimonial value for C-14 dates (e.g. Steuer and Tempel, 1968), or one can try to go further by calculating average dates, assuming (for the most part incorrectly) that the chance of a date being too young is equal to its chance of being too old (Neustupný, 1968). The danger in this procedure is that one loses sight of the individual character of each determination: in fact one sample is much more securely associated and more closely contemporary with finds of a particular cultural phase than another, and the chance of contamination or admixture is different for each sample.Another problem is that the number of C-14 dates that one must take into consideration is often so large that they cannot be digested without some form of graphic presentation, and for this there is as yet no uniformity of practice.

An attempt has been made to assemble the large number of C14 dates measured in Groningen since the last date list was published in 1958. We have not succeeded in preparing all the measurements done in this time; the present list contains a more or less random selection. It is hoped the rest will be included in next year's list.

In late 1962 the old radiocarbon laboratory in Groningen was demolished and new dating equipment was erected in an underground cellar specially built for the purpose.