THE EFFECT OF A SUCCESSION OF OCEAN VENTILATION CHANGES ON C-14

Using the model of Stocker and Wright (1996), we investigate the effec t of a succession of ocean ventilation changes on the atmospheric conc entration of radiocarbon, Delta(14)C(atm), the surface reservoir ages, the top-to-bottom age differences, and the calendar-C-14 age relation ships in different regions of the ocean. The model includes a represen tation of the cycling of C-14 through the atmosphere, the ocean and th e land biosphere. Ocean ventilation changes are triggered by increasin g rates of freshwater discharge into the North Atlantic, which are det ermined according to a simple feedback mechanism between the melting r ates and the climatic state of the North Atlantic region. The results demonstrate that ventilation changes can cause Delta(14)C(atm) fluctua tions of 25 parts per thousand, surface reservoir age fluctuations of 100 yr in the Pacific (200 yr in the Atlantic) and top-to-bottom age v ariations of 500 yr in the Pacific (1000 yr in the Atlantic). We also show that C-14 age estimates based on marine organisms that live in th e near-surface region of the ocean and take up the signal of surface C -14 can result in apparent ago reversals if the assumption of a consta nt reservoir age is made.