Master Thesis Defense by Mathias Winther Kjeldsen

Title: A refined signal of abrupt climate change in the last glacial period

Abstract:
The signal from several incidents of abrupt climate change are preserved in the Greenland ice cores. During the last glacial period, the climate oscillated from cold stadials into warmer interstadials – referred to as Dansgaard-Oeschger (DO) events – and back into the cold. The transitions into interstadials were extremely rapid increasing Greenland temperature up to 16.5°C in decades. A variety of proxies from the ice core records allow us to study the patterns of these climatic changes. Since the transitions happen so fast, noise in the proxy signal poses a challenge when studying them. This study aims to refine the signal by stacking three ice cores into one combined record and investigate the patterns of the proxies and the sequence of the climatic changes. There is somewhat agreement that the Atlantic Meridional Overturning Circulation (AMOC) plays an important role at the onset of the DO events, but despite much effort the ultimate trigger of the events remains elusive. Considering present concerns about the resilience of the AMOC and the stability of the Earth system in general, it is absolutely relevant to improve and understand whatever record describing sudden changes in the system. This study manages to refine a proxy record by stacking of ice core records and hereby infer a phasing of proxies that indicates an AMOC induced shift in the Intertropical Convergence Zone (ITCZ) initially affecting weather patterns and eventually inducing the dramatic temperature increases in Greenland.

Supervisors: Anders Svensson and Sune Olander Rasmussen
Censor: Sebastian Bjerregaard Simonsen (DTU)