Geoscientific Model Development Discussions www.geosci-model-dev-discuss.net 1991-9611 1991-962X 3 1 2010 10.5194/gmdd-3-273-2010 http://www.geosci-model-dev-discuss.net/3/273/2010/ http://www.geosci-model-dev-discuss.net/3/273/2010/gmdd-3-273-2010.html http://www.geosci-model-dev-discuss.net/3/273/2010/gmdd-3-273-2010.pdf 273 307 2010-02-25 Internally generated millennial-scale climate variability in an earth system model of intermediate complexity: sensitivity to ocean bathymetry and orbital forcing T. Friedrich tobiasf@hawaii.edu A. Timmermann L. Menviel O. Timm A. Mouchet D. M. Roche IPRC, University of Hawaii, 2525 Correa Road, Honolulu, HI 96822, USA Département Astrophysique, Géophysique et Océanographie, Université de Liège, Liège, Belgium Section Climate Change and Landscape Dynamics, Department of Earth Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands The effect of orbital variations on simulated millennial-scale variability of the Atlantic Meridional Overturning Circulation (AMOC) is studied using the earth system model of intermediate complexity LOVECLIM. It is found that for present-day topographic boundary conditions low obliquity values (~22.1°) favor the triggering of internally generated millennial-scale variability in the North Atlantic region. Reducing the obliquity leads to changes of the pause-pulse ratio of the corresponding AMOC oscillations. 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