ABSTRACT: Variation of Labrador Sea Water formation over the Last Glacial cycle in a climate model of intermediate complexity.

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Abstract

The variation of North Atlantic Deep Water (NADW) formation over the Last Glacial cycle, from Oxygen Isotopic Substage 5e (OIS-5e; the Eemian) to future global warming projections, is investigated using the UVic Earth System Climate Model. The results are compared with available micropaleontological and stable isotope proxy paleo-reconstructions. 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 all global warming projections, the LSW formation initially ceases as atmospheric CO2 rises, but recovers once the level is held fixed in the atmosphere. Convection in the north extends further into the Nordic Seas as the sea ice edge retreats. In all simulations convection remains active in the eastern North Atlantic, with its latitude depending on the position of the sea ice edge, suggesting that the formation of lower NADW is a robust feature of Late Quaternary climate. As the Labrador Sea is found to be very sensitive to the freshwater forcing, it suggests that this region represents an ideal location for the concentration of observational studies to monitor a possible oceanic response to anthropogenic climate change.

Bibliography of Canadian Geomorphology