The Effect of a Succession of Ocean Ventilation Changes on 14C

Abstract

Using the model of Stocker and Wright (1996), we investigate the effect of a succession of ocean ventilation changes on the atmospheric concentration of radiocarbon, Delta-14C(atm), the surface reservoir ages, the top-to-bottom age differences, and the calendar-14C age relationships in different regions of the ocean. The model includes a representation of the cycling of 14C through the atmosphere, the ocean and the land biosphere. Ocean ventilation changes are triggered by increasing rates of freshwater discharge into the North Atlantic, which are determined according to a simple feedback mechanism between the melting rates and the climatic state of the North Atlantic region. The results demonstrate that ventilation changes can cause Delta-14C(atm) fluctuations of 25%, surface reservoir age fluctuations of 100 yr in the Pacific (200 yr in the Atlantic) and top-to-bottom age variations of 500 yr in the Pacific (1000 yr in the Atlantic). We also show that 14C age estimates based on marine organisms that live in the near-surface region of the ocean and take up the signal of surface 14C can result in apparent age reversals if the assumption of a constant reservoir age is made.