Climate of the Past Discussions www.clim-past-discuss.net 1814-9340 1814-9359 5 4 2009 10.5194/cpd-5-1751-2009 http://www.clim-past-discuss.net/5/1751/2009/ http://www.clim-past-discuss.net/5/1751/2009/cpd-5-1751-2009.html http://www.clim-past-discuss.net/5/1751/2009/cpd-5-1751-2009.pdf 1751 1762 2009-07-01 Strong indications for nonlinear dynamics during Dansgaard-Oeschger events H. Braun holger.braun@iup.uni-heidelberg.de Heidelberg Academy of Sciences and Humanities, Heidelberg, Germany Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Denmark Many climate records show the occurrence of large amplitude (10–15 K), millennial-scale warming events during glacial times, the Dansgaard-Oeschger (DO) events. So far these events have almost exclusively been investigated by means of linear time series analysis. The scope of this paper is to test if the assumption of linearity is fulfilled during DO events. By means of a surrogate-based Monte Carlo method, I here demonstrate that the 60 000-year long δ¹⁸O-record from the NGRIP ice core from Greenland allows to reject the null hypothesis of linearity beyond any reasonable level of doubt. Instead, the ice core record supports the interpretation that the events represent regime switches between different states of operation of glacial climate. As a conclusion, future studies on DO events should focus on the development and the application of more adequate (i.e., nonlinear) methods of time series analysis. Alley, R., Marotzke, J., Nordhaus, W., Overpeck, J., Peteet, D., Pielke Jr., R., Pierrehumbert, R., Rhines, P., Stocker, T., Talley, L., and Wallace, J.: Abrupt Climate Change, Science 299, 2005–2010, 2003. Bond, G., Broecker, W., Johnsen, S., McManus, J., Labeyrie, L., Jouzel, J., and Bonani, G.: Correlations between climate records from North Atlantic sediments and Greenland ice, Nature, 365, 143–147, 1993. Broecker, W. S., Peteet, D. M., and Rind, D.: Does the ocean-atmosphere system have more than one stable mode of operation?, Nature, 315, 21–26, 1985. Dansgaard, W., Clausen, H. B., Gundestrup, N., Hammer, C. U., Johnsen, S. F., Kristinsdottir, P. M., and Reeh, N.: A New Greenland Deep Ice Core, Science, 218, 1273–1277, 1982. Ditlevsen, P. D., Andersen, K. K., and Svensson, A.: The DO-climate events are probably noise induced: statistical investigation of the claimed 1470 years cycle, Clim. Past, 3, 129–134, 2007. Grootes, P. M. and Stuiver, M.: Oxygen 18/16 variability in Greenland snow and ice with 10³ to 10$^5$-year time resolution, J. Geophys. Res., 102, C12, 26455–26470, 1997. Grootes, P. M., Stuiver, M., White, J. W. C., Johnsen, S., and Jouzel, J.: Comparison of oxygen isotope records from the GISP2 and GRIP Greenland ice cores, Nature, 366, 552–554, 1993. Kantz, H. and Schreiber, T.: Nonlinear time series analysis, Cambridge Nonlinear Science Series No. 7, Cambridge University Press, Cambridge UK, 1997. Marwan, N. and Kurths, J.: Nonlinear analysis of bivariate data with cross recurrence plots, Phys. Lett. A, 302, 299–307, 2002. Marwan, N., Romano, M. C., Thiel, M., and Kurths, J.: Recurrence plots for the analysis of complex systems, Physics Reports 438, doi:10.1016/j.physrep.2006.11.001, 2007. Muscheler, R. and Beer, J.: Solar forced Dansgaard/Oeschger events?, Geophys. Res. Lett., 33, L20706, doi:10.1029/2006GL026779, 2006. Oeschger, H., Beer, J., Siegenthaler, U., Stauffer, B., Dansgaard, W., and Langway, C. C.: Late glacial climate history from ice cores, in: Climate Processes and Climate Sensitivity, Geophys. Monogr. Ser., 5, edited by: Hansen, J. E. and Takahashi, T., 299–306, AGU, Washington, DC, 1984. Schulz, M.: On the 1,470-year pacing of Dansgaard-Oeschger warm events, Paleoceanography, 17(2), 1014, doi:10.1029/2000PA000571, 2002. Spötl, C. and Mangini, A.: Stalagmite from the Austrian Alps reveals Dansgaard–Oeschger events during isotope stage 3: Implications for the absolute chronology of Greenland ice cores, Earth Planet. Sc. Lett., 203, 507–518, 2002. Svensson, A., Andersen, K. K., Bigler, M., Clausen, H. B., Dahl-Jensen, D., Davies, S. M., Johnsen, S. J., Muscheler, R., Parrenin, F., Rasmussen, S. O., Röthlisberger, R., Seierstad, I., Steffensen, J. P., and Vinther, B. M.: A 60 000 year Greenland stratigraphic ice core chronology, Clim. Past, 4, 47–57, 2008.