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Climate of the Past An interactive open-access journal of the European Geosciences Union

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Clim. Past Discuss., 5, 2019-2051, 2009
© Author(s) 2009. This work is distributed
under the Creative Commons Attribution 3.0 License.
28 Jul 2009
Review status
This discussion paper has been under review for the journal Climate of the Past (CP). A final paper in CP is not foreseen.
Orbital modulation of millennial-scale climate variability in an earth system model of intermediate complexity
T. Friedrich1, A. Timmermann1, O. Timm1, A. Mouchet2, and D. M. Roche3
1IPRC, University of Hawaii, 2525 Correa Road, Honolulu, HI 96822, USA
2Département Astrophysique, Géophysique et Océanographie, Université de Liège, Liège, Belgium
3Section Climate Change and Landscape Dynamics, Department of Earth Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands

Abstract. 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.

Citation: Friedrich, T., Timmermann, A., Timm, O., Mouchet, A., and Roche, D. M.: Orbital modulation of millennial-scale climate variability in an earth system model of intermediate complexity, Clim. Past Discuss., 5, 2019-2051, doi:10.5194/cpd-5-2019-2009, 2009.
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