CPD Climate of the Past Discussions CPD Clim. Past Discuss. 1814-9359 Göttingen, Germany 10.5194/cpd-5-2019-2009 Orbital modulation of millennial-scale climate variability in an earth system model of intermediate complexity Friedrich T. 1 Timmermann A. 1 Timm O. 1 Mouchet A. 2 Roche D. M. 3 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 28 07 2009 5 4 2019 2051 Copyright: © 2009 T. Friedrich et al. 2009 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://cp.copernicus.org/preprints/5/2019/2009/cpd-5-2019-2009.html The full text article is available as a PDF file from https://cp.copernicus.org/preprints/5/2019/2009/cpd-5-2019-2009.pdf

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. Stochastic excitations of the density-driven overturning circulation in the Nordic Seas can create regional sea-ice anomalies and a subsequent reorganization of the atmospheric circulation. The resulting remote atmospheric anomalies over the Hudson Bay can release freshwater pulses into the Labrador Sea leading to a subsequent reduction of convective activity. The millennial-scale AMOC oscillations disappear if LGM bathymetry (with closed Hudson Bay) is prescribed. Furthermore, our study documents the marine and terrestrial carbon cycle response to millennial-scale AMOC variability. Our model results support the notion that stadial regimes in the North Atlantic are accompanied by relatively high levels of oxygen in thermocline and intermediate waters off California – in agreement with paleo-proxy data.

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