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Reduced Stability of the Atlantic Meridional Overturning Circulation due to Wind Stress Feedback during Glacial Times
 

Summary: Reduced Stability of the Atlantic Meridional Overturning Circulation due to
Wind Stress Feedback during Glacial Times
OLIVIER ARZEL, MATTHEW H. ENGLAND, AND WILLEM P. SIJP
Climate Change Research Centre, School of Mathematics and Statistics, University of New South Wales,
Sydney, New South Wales, Australia
(Manuscript received 18 October 2007, in final form 3 February 2008)
ABSTRACT
A previous study by Mikolajewicz suggested that the wind stress feedback stabilizes the Atlantic ther-
mohaline circulation. This result was obtained under modern climate conditions, for which the presence of
the massive continental ice sheets characteristic of glacial times is missing. Here a coupled ocean­
atmosphere­sea ice model of intermediate complexity, set up in an idealized spherical sector geometry of
the Atlantic basin, is used to show that, under glacial climate conditions, wind stress feedback actually
reduces the stability of the meridional overturning circulation (MOC). The analysis reveals that the influ-
ence of the wind stress feedback on the glacial MOC response to an external source of freshwater applied
at high northern latitudes is controlled by the following two distinct processes: 1) the interactions between
the wind field and the sea ice export in the Northern Hemisphere (NH), and 2) the northward Ekman
transport in the tropics and upward Ekman pumping in the core of the NH subpolar gyre. The former
dominates the response of the coupled system; it delays the recovery of the MOC, and in some cases even
stabilizes collapsed MOC states achieved during the hosing period. The latter plays a minor role and
mitigates the impact of the former process by reducing the upper-ocean freshening in deep-water formation

  

Source: Arzel, Olivier - Climate Change Research Centre, University of New South Wales
England, Matthew - Climate Change Research Centre & School of Mathematics and Statistics, University of New South Wales

 

Collections: Environmental Sciences and Ecology; Geosciences