Radiocarbon as a diagnostic tracer in ocean and carbon cycle modeling

Models which are used to study the evolution of oceanic anthropogenic CO2 uptake in a warmer climate need to be adequately tested before their results are used to influence science and national policy, let alone predict future regional climate. In order to study circulation and the redistribution of carbon in the ocean, we have simulated the uptake and redistribution of bomb radiocarbon in a state of the art ocean general circulation model. The model does reasonably well in simulating the gross surface prebomb distribution of radiocarbon as well as some of the finer details resolved during Geochemical Ocean Section Study and World Ocean Circulation Experiment observations. In areas of downwelling the simulated surface-ocean bomb C-14 maxima occur too early with too much amplitude. This indicates inadequate vertical mixing and coupling between the wind driven and deeper regions of the ocean with a piling up of radiocarbon and CO2 in the upper ocean. This inadequacy will hamper efforts to predict ocean CO2 uptake on decadal to centennial timescales, the equivalent ventilation time of the respective water masses. These results are not specific to our model and indicate a systemic problem in many ocean models.