The Maunder Minimum: An interlaboratory comparison of Delta C-14 from AD 1688 to AD 1710

Measurements on same-age tree-ring samples from proximal Ural Mountain tree s by the Ioffe Institute research group and at the University of Arizona de monstrate a variance corresponding to a standard deviation of +/-5.1 parts per thousand for Ioffe compared to +/-2.1 parts per thousand for Tucson. Th ere is also a calibration difference of 4.3 +/- 1.2 <(sigma)over bar>parts per thousand. Comparison of the same years measured in Seattle on wood from the Pacific Northwest shows an offset of 2.2 +/- 0.5 <(sigma)over bar>part s per thousand. This is not a calibration error, but rather is expected fro m the well-documented evidence for divergence and upwelling of C-14-deplete d CO2 along the west coast of North America.