Strong indications for nonlinear dynamics during Dansgaard-Oeschger events
Heidelberg Academy of Sciences and Humanities, Heidelberg, Germany
Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Denmark
Received: 31 May 2009 – Accepted for review: 11 Jun 2009 – Discussion started: 01 Jul 2009
Abstract. 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.
Braun, H.: Strong indications for nonlinear dynamics during Dansgaard-Oeschger events, Clim. Past Discuss., 5, 1751-1762, doi:10.5194/cpd-5-1751-2009, 2009.