Modeling the effect of abrupt ocean circulation change on marine reservoir age

Radiocarbon surface reservoir age is required for precise dating of marine organisms. Although often assumed constant, changes in atmospheric radiocarbon content, ocean circulation, and ocean mixing imprint changes on this quantity. The spatial and temporal variations of marine surface and bottom reservoir ages in response to a shutdown and subsequent recovery of Atlantic meridional overturning circulation (MOC) are analyzed using a cost-efficient, three-dimensional ocean circulation model. Generally, surface reservoir age changes are limited to the Atlantic Ocean with a reduction of about 100 yr after the MOC shutdown, followed by a slow increase and a peak at the time of MOC resumption. Parameter sensitivity studies with respect to the roles of gas exchange, diffusivity and North Atlantic ice cover show that ice cover has the largest effect on the transient evolution of surface reservoir age during the shutdown. Our model results agree well with a recent reconstruction of surface reservoir age changes during the Younger Dryas when we reduce the rate of gas exchange in the model and include a parametrization of seasonal ice cover in the North Atlantic.