REVISITING THE SEA-SAW DURING THE DEGLACIATION

Coral records of the sea-level rise that accompanied the last deglaciation have shown evidence of a prominent meltwater pulse, labelled MWP-1A, shortly before 13,800 calendar years before present (BP). Since relatively warm conditions prevailed in the Northern Hemisphere between the onset of the Bølling warm phase until the Younger Dryas (i.e. between 14,600 and 12,700 years BP), this discovery questioned earlier interpretations assuming that such meltwater pulses triggered shut-off of the oceanic thermohaline circulation and, subsequently, abrupt coolings in the Northern Hemisphere. Here, we adress this issue with transient simulations of the last deglaciation performed with an ocean-atmosphere-ice sheet coupled model. Special attention has been paid to the consequences of Heinrich Event 1 (HE1) on the climatic evolution. It is suggested that the abrupt warming recorded in the Sajama Bolivian ice core near 14,600 years BP was simultaneous to the onset of the Bølling warm phase, both events resulting from an overshoot of the ocean circulation. The model also simulates a major meltwater pulse near 14,600 years BP, but although the amplitude of the latter is much larger than the one associated to HE1, it does not perturb significantly the formation of North Atlantic Deep Water.