Master Thesis defense by Anna Maria Klüssendorf

Title: Bipolar Phasing of Abrupt Climate Change During the Last Glacial Period


The Last Glacial Period is characterised by a strong climate variability, where millennial-scale warming events identified in paleoclimatic data from the Greenland ice sheet have interrupted the cold glacial climate. These abrupt climate changes are a typical example for pre-historic tipping points in the climate system with global consequences. Presumably initiated in the North Atlantic region, atmospheric and oceanic interhemispherical coupling result in fi ngerprints of the Northern Hemisphere warming events to modulate the temperature in Antarctica. According to the bipolar see-saw hypothesis, the hemispheres are in distinct anti-phase, with Antarctic temperature decreases lagging Greenland abrupt warming. Despite being related to oscillations in the strength of the Atlantic Meridional Ocean Circulation, the physical mechanisms underlying the climate fluctuations, however, are not yet fully understood. With progressive modern climate change, the need for a comprehensive understanding of the processes behind abrupt changes has increased in order to drive climate models predicting possible tipping points. As one main feature of the pre-historic temperature fluctuations, this study approaches the bipolar phasing between Antarctica and Greenland over stadial-interstadial transitions. For this purpose, the onsets of 33 Greenland interstadials associated with Dansgaard-Oeschger (DO) events during the entire last glacial are defi ned in the NGRIP stable oxygen isotope record. This enables the determination of the Antarctic response time relative to Greenland temperature rises. Based on bipolar volcanic synchronisation, the Antarctic average response time is reduced compared to previous studies. Investigating the climate across different groups of DO events classified by the time of occurrence and size, possible processes provoking the abrupt changes are assessed. The climate interpretation is further extended by a comparison between the ice core records and temperature pro les provided by a global climate model simulating DO events under distinct CO2 forcing. This suggests a tight connection between abrupt temperature rises and rapid sea ice retreat in the North Atlantic and Northern Seas. Therefore, this work discusses the potential for future abrupt climate changes as experienced during the last ice age under ongoing anthropogenic climate change.

Supervisor: Anders Svensson
Censor: Nanna B. Karlsson (GEUS)