TEMPORAL-GEOGRAPHICAL MELTWATER INFLUENCES ON THE NORTH-ATLANTIC CONVEYOR - IMPLICATIONS FOR THE YOUNGER DRYAS

The temporal and geographical roles of meltwater discharge (from the L aurentide ice sheet) on North Atlantic Deep Water (NADW) production ar e investigated utilizing a global, realistic geometry, coupled climate model which does not require the use of flux adjustments. Model resul ts suggest that preconditioning by meltwater discharge (to the Mississ ippi) prior to the Younger Dryas (YD) is capable of pushing NADW beyon d the limit of its sustainability. The diversion of meltwater to the S t. Lawrence then merely serves to completely inhibit NADW production. The modeled change in surface air temperature generally agrees with th e global pattern and magnitude of temperature change seen in paleoclim atic reconstructions of the YD and is intimately linked to changes in NADW formation. The global thermohaline circulation provides an interh emispheric teleconnection with the Southern Oceans, while changes in t he atmospheric heat transport (reacting to a global redistribution of oceanic heat transport) provide a mechanism for interbasin teleconnect ion. Although the primary thermodynamic and hydrological cycle feedbac k processes are included within the atmospheric model, in the absence of additional feedbacks an equilibrium without the presence of NADW is possible. The inclusion of the wind stress/speed feedback is found to significantly contribute to the resumption of NADW production, as sug gested by previous studies. Contrary to these same studies, however, t he coupled model indicates an advective spin-up timescale is required for resumption of NADW production and hence the termination of the mod eled YD-like climate event (as opposed to a decadal-century timescale) . The reason for the discrepancy is unclear but may be associated with the use of fixed salt flux fields applied in previous studies, or the duration, strength, and geographical location of the imposed meltwate r applied.