Ocean Sci. Discuss., 10, 1895-1931, 2013
www.ocean-sci-discuss.net/10/1895/2013/
doi:10.5194/osd-10-1895-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Ocean Science (OS). Please refer to the corresponding final paper in OS.
The role of subpolar deep water formation and Nordic Seas overflows in simulated multidecadal variability of the Atlantic overturning
K. Lohmann1, J. H. Jungclaus1, D. Matei1, J. Mignot2,3, M. Menary4, H. R. Langehaug5,6, J. Ba7, Y. Gao5,6, O. H. Otterå6,8, W. Park7, and S. Lorenz1
1Max Planck Institute for Meteorology, Hamburg, Germany
2LOCEAN, Institute Pierre Simon Laplace, University Pierre and Marie Curie, Paris, France
3Climate and Environmental Physics, and Oeschger Centre of Climate Change Research, University of Bern, Switzerland
4Met Office Hadley Center, Exeter, UK
5Nansen Environmental and Remote Sensing Center, Bergen, Norway
6Bjerknes Centre for Climate Research, Bergen, Norway
7Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
8Uni Research, Bergen, Norway

Abstract. We investigate the respective role of variations in subpolar deep water formation and Nordic Seas overflows for the decadal to multidecadal variability of the Atlantic meridional overturning circulation (AMOC). This is done by analysing long (order of 1000 yr) control simulations with five coupled climate models as well as sensitivity experiments performed with one of the models, in which we suppress the variability of either subpolar deep water formation or Nordic Seas overflows. For all models, the maximum influence of variations in subpolar deep water formation is found at about 45° N, while the maximum influence of variations in Nordic Seas overflows is rather found at 55° N to 60° N. Regarding the two overflow branches, the influence of variations in the Denmark Strait overflow is, for all models, substantially larger than that of variations in the overflow across the Iceland–Scotland–Ridge. The influence of variations in subpolar deep water formation is, on multi-model average, larger than that of variations in the Denmark Strait overflow. This is true both at 45° N, where the maximum standard deviation of decadal to multidecadal AMOC variability is located for all but one model, and at the more classical latitude of 30° N. At 30° N, variations in subpolar deep water formation and Denmark Strait overflow explain, on multi-model average, about half and one third respectively of the decadal to multidecadal AMOC variance.

Citation: Lohmann, K., Jungclaus, J. H., Matei, D., Mignot, J., Menary, M., Langehaug, H. R., Ba, J., Gao, Y., Otterå, O. H., Park, W., and Lorenz, S.: The role of subpolar deep water formation and Nordic Seas overflows in simulated multidecadal variability of the Atlantic overturning, Ocean Sci. Discuss., 10, 1895-1931, doi:10.5194/osd-10-1895-2013, 2013.
 
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