Importance of ice-ocean interactions for the global ocean circulation: A model study

Numerical experiments are conducted with a coarse-resolution global ice-oce an model in order to determine to what degree the sea ice-ocean exchanges o f heat, salt/freshwater, and momentum control the general circulation of th e world ocean on long timescales. These experiments reveal that the formati on of North Atlantic Deep Water (NADW) in the model results from the strong heat losses that occur at the oceanic surface in the high-latitude North A tlantic. The large-scale ice-ocean interactions have nearly no influence on this process. In particular, neglecting the freshwater flux associated wit h the southward ice transport at Fram Strait does not impact seriously on t he salinity of the Greenland and Norwegian Seas. At equilibrium the absence of this freshwater flux is balanced by an enhanced oceanic freshwater tran sport from the Arctic. Furthermore, it appears that the model NADW formatio n does not critically depend on the media (ice or ocean) transporting the f reshwater. Besides, both the salt/freshwater and heat exchanges between sea ice and ocean are crucial in the Southern Ocean for the deep water product ion, properties, and export. The large amount of brine released during ice formation on the model Antarctic continental shelf leads to very high salin ities there. The resulting dense shelf waters are then transported toward g reat depths after some mixing with ambient waters, finally forming the Anta rctic Bottom Water body. On the other hand, the net ice melting associated with ice convergence in some areas, such as the southwestern Pacific, stabi lizes the water column and forbids deep mixing in these regions. Furthermor e, the contact with the ice imposes that the polar surface waters must be m aintained very close to their freezing point temperature. Our results sugge st that this process takes an important part in increasing the density of t he Antarctic Bottom Water. We also show that the modifications of the stres s at the ocean surface induced by the internal ice stress have only a regio nal effect.