A source-weighted Benthic minus Planktonic radiocarbon method for estimating pure ocean water age

This paper introduces the Benthic minus-weighted-Planktonic (BwP) age method to estimate the pure water age of the deep ocean. It combines radiocarbon data with water mass composition evolution in an ocean model under realistic surface forcings accounting for multiple water sources, marine reservoir age, and the evolving atmospheric \({14\atop}C\) content. Instead of using local planktonic radiocarbon age, the source water radiocarbon age is derived from global planktonic data weighted by their water mass contributions, with weights simulated by dye tracers. An iterative approach is used to account for the effect of the temporal variation of the atmospheric radiocarbon or the so-called projection age issue. In this ocean model, we demonstrate that our BwP age effectively reproduces the pure water age that results from the interior ocean circulation. Preliminary application to the North Pacific suggests that the pure water age at the Last Glacial Maximum (LGM) is not much older than today.