The Suki Manabe Symposium

1.3

Climate change associated with melting events in the northern and southern hemispheres

Andrew J Weaver, University of Victoria, Victoria, BC, Canada

The variation of North Atlantic Deep Water (NADW) formation over the Last Glacial cycle is investigated using the UVic Earth System Climate Model. Equilibrium simulations for the Eemian (125 kyr BP) and the Last Glacial Maximum (LGM--21 kyr BP) both reveal the absence of Labrador Sea Water (LSW) formation although NADW formation still occurs, albeit at a reduced rate relative to the modern times. For the Eemian, the location of convection in the eastern North Atlantic is similar to the present, although it is generally shallower and less extensive. In the case of the LGM, deep convection has moved southward to the western coast of Europe and is much more localised. The inferred inception of a modern-like circulation slightly before 7 kyr BP revealed by proxy reconstructions is not captured by the model unless the meltwater forcing from the Laurentide ice sheet is applied in a long transient simulation. This raises questions concerning the applicability of equilibrium simulations in capturing the early Holocene climate. In addition the link is explored between Meltwater pulse 1A (mwp-1A) and the onset of the Bolling-Allerod (Bollerod) event (14,600 yr BP). It is demonstrated that if a large component of mwp-1A occurs in the Southern Hemisphere, the strength of the Atlantic Meridional Overturning (AMO) increases, thereby warming the North Atlantic region and providing an explanation for the onset of the Bollerod. This finding, together with its associated hysteresis behaviour, underlines the significance of the understudied Antarctic Intermediate Water formation in controlling the strength of the AMO.

Session 1, Suki Manabe Symposium
Monday, 10 January 2005, 9:00 AM-5:15 PM

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