Regional 14 CO 2 Offsets in the Troposphere: Magnitude, Mechanisms, and Consequences

Radiocarbon dating methods typically assume that there are no significant tropospheric 14 CO 2 gradients within the low- to mid-latitude zone of the Northern Hemisphere. Comparison of tree ring 14 C data from southern Germany and Anatolia supports this assumption in general but also documents episodes of significant short-term regional 14 CO 2 offsets. We suggest that the offset is caused by an enhanced seasonal 14 CO 2 cycle, with seasonally peaked flux of stratospheric 14 C into the troposphere during periods of low solar magnetic activity, coinciding with substantial atmospheric cooling. Short-term episodes of regional 14 CO 2 offsets are important to palaeoclimate studies and to high-resolution archaeological dating.