Reviewing the Mid-First Millennium BC 14C “warp” using 14C/bristlecone pine data

AMS-based 14C measurements have been obtained on 53 dendrochronologically-dated Bristlecone pine (Pinus longaeva) wood samples in decadal increments spanning 2300-2750 cal BP with particular interest focused on the decades centered on 2405 cal BP and 2625 cal BP. In general, there is overall agreement with the current IntCal04/09 consensus calibration curve for this period. For the 2400-2410 cal BP interval, our Bristlecone-based 14C value is consistent with the 14C value obtained by Belfast on Irish oak for that decade but not on German oak values obtained by Seattle. Our 14C value for the 2620-2630 cal BP interval is consistent with the German oak (Heidelberg)-based 14C decadal value. The 10Be-based reconstruction of 14C variations over the 2620-2630 cal BP interval also supports the Heidelberg data although clearly additional clarifications are required before the current tree ring-based 14C and ice core-based 10Be data for this interval can be accurately interpreted and valid inferences obtained.