Tree-ring and varve scales combined, c. 13500 B.C. to A.D. 1977
Abstract Varve chronologies are of several kinds but glacial varves respond to summer temperature and fluvial varves to summer rainfall. Tree-ring chronologies near the timberline respond to summer temperature but European oak chronologies respond to summer rainfall. Certain global features of the weather of the summer season, notably the Biennial Index, are therefore parameters that can be used for cross-dating both varves and tree-rings in different continents. Characteristic curves for different parameters in the Late Glacial (Zones Ia, Ib and II) and in the past thousand years are presented. A moisture curve is given for the North European Plain (200 B.C.–A.D. 1100). A conversion chart for tree-rings and radiocarbon dates is extended back into the Late Glacial on the tentative assumption that the radiocarbon error was about 950 years at the beginning of the Holocene (III/IV), i.e. that 10300 b.p. should be 11250 B.P. or 9300 B.C. Supplementary sources of information useful in obtaining approximate dates include: (a) palaeomagnetism; (b) tephrochronology and X-ray analysis; (c) cycle analysis; (d) climatic peculiarities associated with specific radiocarbon centuries; (e) X-ray analysis of specific varves; and (f) new methods of varve-analysis. The varve-series used for the Late Glacial, if the author's cross-dating between North America and Scandinavia is acceptable, constitute a floating chronology of about 4000 years. Given approximate 14 C dates for any long series of varves or tree-rings in one part of the world, it is now possible to obtain cross-dating with any other long series in another part of the world, and it will be easy to replace the tentative ‘950-year’ error by a precise figure determined from a combined varve and tree-ring scale extending back from the present day to (say) the zero of Sauramo's scale for varves in Finland. In the meantime the ‘950’ is mnemonically convenient, as this would make the year on the B.C. scale one thousand less than the year on the b.p. scale.