Modelling the Northern Hemisphere Climate and Ice Sheets during the

• Main Authors: Last Deglaciation, Lauren J. Gregoire
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2010
• Subjects: Ice Sheet
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.651.1828; http://homepages.see.leeds.ac.uk/~earljg/documents/Thesis_L_Gregoire_final.pdf

Over the past 1.8 Million years, climate has oscillated between cold and warm states, causing large ice sheets to build up and decay in the Northern Hemisphere, but we do not fully understand the mechanisms and feedbacks which are important. Cli-mate and ice sheet modelling can help improve our understanding of how changes in the Earth’s orbit and atmospheric CO2 concentrations contributed to these glacial-interglacial cycles. In this thesis, we evaluate the forcings of the Northern Hemi-sphere deglaciation using the FAMOUS low resolution general circulation model and the Glimmer ice sheet model. First, we performed a tuning of FAMOUS to improve the present day and Last Glacial Maximum (LGM; 21 kyr BP) climates and evaluate the uncertainty in the modelling. Using a Latin Hypercube Sampling method, we created an ensemble of 100 model configurations, and evaluated this ensemble against present day and LGM data. We obtained 10 optimal configurations, with more realistic LGM ocean circulation and higher sensitivities to LGM boundary conditions than the original configuration. We then built up the LGM ice sheets through the last glacial cycle, by interpo-lating present day and LGM equilibrium climate runs with a climate index. Sensi-tivity tests to input climate, run using the ensemble of tuned FAMOUS simulations, showed that the Eurasian ice sheet was particularly sensitive to the climate forcing. Starting with our LGM ice sheets, we modelled the deglaciation (21-9 kyr BP) by forcing Glimmer with a transient simulation from Kahana et al. (in prep.). We found that the separation of the Laurentide and Cordilleran ice sheets generated a meltwater flux equivalent in terms of timing and amplitude to Meltwater Pulse 1a. The orbital forcing contributed to around two thirds of the deglaciation of North America, while the CO2 forcing contributed to one third.