The role of the atmosphere on Northern Hemisphere ice sheet evolution during the late Pleistocene

• Main Author: Niu, Lu
• Other Authors: Lohmann, Gerrit, Schulz, Michael
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Bremen 2019
• Subjects: Northern Hemisphere ice sheets; Ice sheet modelling; Coupled climate-ice sheet modelling; The glacial-interglacial cycles; Dansgaard-Oeschger events; Marine Isotope Stage 13; 500; 500 Science; ddc:500; Eisschild*; Ice Sheet
• Online Access: https://media.suub.uni-bremen.de/handle/elib/1738; https://nbn-resolving.org/urn:nbn:de:gbv:46-00108568-17

During the late Pleistocene, the Northern Hemisphere ice sheets waxed and waned with a periodicity of around 100 kyr. They are among the largest topographic features that can amplify, pace or drive global climate change on different time scales. Studying ice sheet-climate feedback through numerical modelling is necessary for understanding the physical mechanisms of the Earth system. As mainly land-based ice sheets, the role of the atmosphere on Northern Hemisphere ice sheet evolution during the late Pleistocene is investigated. The evolution of Northern Hemisphere ice sheets through the last glacial cycle is simulated with the glacial index method by using the climate forcing from a general circulation model, COSMOS. By comparing the simulated results to geological reconstructions, we first show that the modelled climate is capable of capturing the main features of the ice-sheet evolution. However, large deviations exist, likely due to the absence of nonlinear interactions between ice sheet and other climate components. The model uncertainties of the climate forcing are examined using the output from nine climate models from the Paleoclimate Modelling Intercomparison Project Phase III. The results show a large variability in simulated ice sheets between the different models. We find that the ice sheet extent pattern resembles summer surface air temperature pattern at the Last Glacial Maximum, confirming the dominant role of surface ablation process for high-latitude Northern Hemisphere ice sheets. This study shows the importance of the upper boundary condition for ice sheet modelling, and implies that careful constraints on climate output is essential for simulating realistic glacial Northern Hemisphere ice sheets. Evidence from proxy records indicates that millenniala scale abrupt climate shifts, called Dansgaard-Oeschger events, happened during past glacial cycles. We show that the Dansgaard-Oeschger events can regulate the mean state of the Northern Hemisphere ice sheets. Sensitivity experiments show that the ...