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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/cp-2019-19
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2019-19
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 25 Feb 2019

Research article | 25 Feb 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Climate of the Past (CP).

Objective extraction and analysis of statistical features of Dansgaard-Oeschger events

Johannes Lohmann and Peter D. Ditlevsen Johannes Lohmann and Peter D. Ditlevsen
  • Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Denmark

Abstract. The strongest mode of centennial to millennial climate variability in the paleoclimatic record are the Dansgaard-Oeschger (DO) cycles. Despite decades of research their dynamics and physical mechanism remain poorly understood. Valuable insights can be obtained by studying high-resolution Greenland ice core proxies, such as the NGRIP δ18O record. However, conventional statistical analysis is complicated by the high noise level, the cause of which is partly due to glaciological effects unrelated to climate, and which is furthermore changing over time. We remove the high-frequency noise and extract the most robust features of the DO cycles, such as rapid warming and interstadial cooling rates, by fitting a consistent piecewise-linear model to three Greenland ice core records. With statistical hypothesis tests we aim to obtain an empirical, mechanistic understanding of what controls the of amplitudes and durations of the DO cycles. To this end, we investigate distributions of and causalities in between different features, as well as modulations of them in time by external climate factors, such as CO2 and insolation. Our analysis suggests different mechanisms underlying warming and cooling transitions due to contrasting distributions and external influences of the stadial and interstadial durations, as well as the fact that the interstadial durations can be predicted to some degree by the linear cooling rates already shortly after interstadial onset.

Johannes Lohmann and Peter D. Ditlevsen
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Johannes Lohmann and Peter D. Ditlevsen
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Latest update: 15 Jul 2019
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Short summary
Greenland ice core records show that the climate of the last glacial period was frequently interrupted by rapid warming events, followed by cooling episodes of vastly different duration. We fit a generic waveform to the noisy ice core record in order to extract a robust climate signal and empirically study what controls amplitude and duration of the warmings and coolings. We find that cooling transitions are more predictable then warmings, and are influenced by different climate forcings.
Greenland ice core records show that the climate of the last glacial period was frequently...
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