Natural Radiocarbon Distribution in the Deep Ocean

We present for the first time objectively mapped natural radiocarbon (14C) abundance in the global deep ocean using mostly new measurements from the World Ocean Circulation Experiment (WOCE). Compared to earlier data from the Geochemical Ocean Sections Study, the new data number almost seven times more. Also, the WOCE data collected during the 1990s have sufficient spatial coverage to make objective mapping meaningful. The new natural ∆14C maps clearly show the deep path of the well-known global thermohaline circulation. We compare the new maps with simulation results from three versions of the Princeton Ocean Biogeochemistry Model, as a means to illustrate how such maps can be used to constrain ocean carbon cycle models. We show that the three Princeton models, which are not necessarily atypical of currently available coarse resolution ocean general circulation models, have a wide range of behavior in simulating the deep natural 14C distribution. Some deviate significantly from the observed in both amplitude and spatial pattern. The same models make significantly different centennial time scale projections of future anthropogenic carbon uptake by the ocean. This highlights the importance of using the new natural 14C data to properly evaluate the performance of ocean carbon cycle models in ventilating the deep ocean.