Readjustment of glacial radiocarbon chronologies by self-consistent three-dimensional ocean circulation modeling

A critical problem in radiocarbon dating is the spatial and temporal variability of marine C-14 reservoir ages. This is particularly true for the time scale beyond the tree-ring calibration range. Here, we propose a method to assess the evolution of marine reservoir ages during the last deglaciation by numerical modeling. We apply a self-consistent iteration scheme in which existing radiocarbon chronologies can be readjusted by transient, three-dimensional simulations of marine and atmospheric Delta C-14. To estimate the uncertainties regarding the ocean ventilation during the last deglaciation, we consider various ocean overturning scenarios which are based on different climatic background states. An example readjusting C-14 data from the Caribbean points to marine reservoir ages varying between 200 and 900 a during the last deglaciation. Correspondingly, the readjustment leads to enhanced variability of atmospheric Delta C-14 by +/- 30 parts per thousand, and increases the mysterious drop of atmospheric Delta C-14 between 17.5 and 14.5 cal ka BP by about 20 parts per thousand. (C) 2011 Elsevier B.V. All rights reserved.