Reconstructing the Global Ocean Ventilation from the Atmospheric Radiocarbon Record Using the Inverse Method


OCCI Project Funded: 2001

Proposed Research

In the modern climate the deficit in the radiative balance of the high latitudes in both hemispheres is partly compensated by poleward heat fluxes in the atmosphere and ocean. A large fraction of the oceanic heat flux in the northern hemisphere occurs in the North Atlantic. Warm waters coming from the tropics are advected to the northern North Atlantic, where they release heat to the atmosphere. The consequent decrease in buoyancy of the surface waters leads to the formation of deep waters, which today contribute to the ventilation of the whole ocean volume. The rate of global ocean ventilation (hereafter GOV) is thus a quantity of prime climatic interest. Here we propose to reconstruct the evolution of the GOV during the last deglaciation, when the ocean-atmosphere system probably experienced significant reorganizations, using recent, high-resolution records of 14C activity and production in the atmosphere. Our assumption is that the atmospheric 14C activity is sensitive to GOV changes, as a significant portion of 14C produced in the atmosphere is introduced into the deep sea during deep-water formation at high latitudes. An inverse method will be used to combine the records of 14C activity and production on the one hand, and the documentation of the climatic changes in the circum-North Atlantic on the other hand, will be tied to the same, accurate time scale (from the GISP2 ice core, central Greenland). Hence we should be able to produce a robust time correlation between these climatic changes and the probable variations in the GOV during the deglaciation. Our study should give insight into the general problem of the potential of the global ocean circulation, and of the North Atlantic circulation in particular, to respond to, or to cause, abrupt climate changes.