The effect of a succession of ocean ventilation changes on (super 14) C.

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 (super 14) C (super atm) , the surface reservoir ages, the top-to-bottom age differences, and the calendar- (super 14) C age relationships in different regions of the ocean. The model includes a representation of the cycling of (super 14) C 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 (super 14) C (super 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 (super 14) C age estimates based on marine organisms that live in the near-surface region of the ocean and take up the signal of surface (super 14) C can result in apparent age reversals if the assumption of a constant reservoir age is made.