An atlas of megadroughts in Europe and in the Mediterranean Basin during the Common Era provides insights into climate variability.

May–June precipitation is the primary limiting factor in annual tree‐ring growth of the oaks of northeastern Greece and northwestern Turkey (39–42°N, 22–37°E). In a regional tree‐ring chronology of historic building and modern forest samples, the May–June precipitation explains at least 40% of the variance for 1900–1985, and is reconstructed here from A.D. 1089–1989. The reconstruction is compared to three other precipitation reconstructions for Turkey. The mean temperature of May and June is also a growth‐limiting factor owing to its effect on the availability of precipitation to the trees, but is more difficult to calibrate and reconstruct accurately owing to the trees' indirect response and the low number of long‐temperature records available for the interior of northwestern Turkey.An analysis of the various methods of manipulating oak tree‐ring data for regional climate reconstruction shows that removing all but the high‐frequency variability plus normalizing the oak data sets before combining them into a master chronology are optimal techniques for a reasonable precipitation reconstruction of the entire area over the instrumental period. However, these methods do remove the low‐frequency signal and dampen some of the evidence of local extremes in May–June precipitation; these issues are discussed here and will be addressed in future research. Copyright © 2007 Royal Meteorological Society

Radiocarbon data suggest the need to reconsider current dates and assumptions for contact-era Iroquoian history.

A single Northern Hemisphere calibration curve has formed the basis of radiocarbon dating in Europe and the Mediterranean for five decades, setting the time frame for prehistory. However, as measurement precision increases, there is mounting evidence for some small but substantive regional (partly growing season) offsets in same-year radiocarbon levels. Controlling for interlaboratory variation, we compare radiocarbon data from Europe and the Mediterranean in the second to earlier first millennia BCE. Consistent with recent findings in the second millennium CE, these data suggest that some small, but critical, periods of variation for Mediterranean radiocarbon levels exist, especially associated with major reversals or plateaus in the atmospheric radiocarbon record. At high precision, these variations potentially affect calendar dates for prehistory by up to a few decades, including, for example, Egyptian history and the much-debated Thera/Santorini volcanic eruption.Downloaded from chronology, D. Brown for supplying the IrO samples from the Queen's University Belfast chronology, D. P. Mielke and P. Hnila for the samples from OYM and sharing 14 C dates on these and for collaboration on this material, and H. Grudd for supplying dendrochronologically dated Swedish pine. We thank C. Kocik and B. Lorentzen for work on the NOC and OYM tree ring samples. We thank M. Baillie for advice on IrOs. We thank the three referees for helpful and constructive comments. We acknowledge the Italian Ministry of Cultural Heritage and Activities (MiBAC) and the Municipality of NOC for supporting the archaeological excavation of the site.

SignificanceWe observe a substantive and fluctuating offset in measured radiocarbon ages between plant material growing in the southern Levant versus the standard Northern Hemisphere radiocarbon calibration dataset derived from trees growing in central and northern Europe and North America. This likely relates to differences in growing seasons with a climate imprint. This finding is significant for, and affects, any radiocarbon application in the southern Levant region and especially for high-resolution archaeological dating—the focus of much recent work and scholarly debate, especially surrounding the timeframe of the earlier Iron Age (earlier Biblical period). Our findings change the basis of this debate; our data point to lower (more recent) ages by variously a few years to several decades.