High precision radiocarbon concentrations in tree rings from Northeastern Mexico: A new record with annual resolution for dating the recent past

We present a new record of atmospheric Delta C-14 from 1926-2002 AD constructed from annual measurements of dendrochronologically dated tree rings from Nuevo Leon in Northeast (NE) Mexico. The results are very similar to the Northern Hemisphere Zone 2 compilation, indicating that this location provides a suitable record of background atmospheric Delta C-14. Closer examination of the atmospheric bomb peak years (1962-1965 AD), however reveals subtle differences from the Zone 2 compilation that may reflect transport of C-14-depleted air from the south during the summer season influenced not only by the northward migration of the Intertropical Convergence Zone but also by the North American Monsoon system and tropical storms and hurricanes over the Gulf of Mexico. These differences decrease after 1965 indicating that Northern Hemisphere atmospheric mixing had largely occurred by this point. Examination of the pre-bomb peak period reveals a steady decrease in (FC)-C-14 associated with fossil fuel derived CO2 emissions from 1922-1950 AD. The NE Mexico record is enriched in C-14 relative to a record from the Pacific Northwest during this period, potentially reflecting a greater impact of fossil fuel emissions and/or release of aged CO2 from Pacific upwelling in this region. This record from NE Mexico represents the longest such record from North America and will contribute to improved characterization of the spatial and temporal variability of atmospheric Delta C-14 in the Northern Hemisphere.