CLIMATE INVESTIGATIONS USING ICE SHEET AND MASS BALANCE MODELS WITH EMPHASIS ON NORTH AMERICAN GLACIATION

CLIMATE INVESTIGATIONS USING ICE SHEET AND

MASS BALANCE MODELS WITH EMPHASIS ON

NORTH AMERICAN GLACIATION

By Sean D. Birkel

Thesis Advisor: Dr. Peter O. Koons

An Abstract of the Dissertation Presented

in Partial Fulfillment of the Requirements for the

Degree of Doctor of Philosophy

(in Earth Sciences)

December, 2010

This dissertation describes the application of the University of Maine Environmental Change Model (UM-ECM) and Ice Sheet Model (UM-ISM) to understanding the small and large-scale glaciation of North America.  The UM-ECM was developed through this research to provide high-resolution solutions of global climate.  The UM-ECM is a flexible tool for both climate research and education, and the web-based interface has been tested with a group of middle school science teachers with a focus on local to global-scale climate learning.  UM-ISM is an existing framework for reconstructing the dynamical evolution of ice sheets.

In the first of two research applications, UM-ISM is driven by climate information from the UM-ECM to reconstruct a Pleistocene glacier system over Wind River Mountains, Wyoming.  The modeled ice cap forms in response to a 5-6 °C cooling in conjunction with a doubling of precipitation relative to modern conditions.  Moreover, when subjected to the present warm climate, the ice cap disappears from the mountain range within 90 years.  These results support hypotheses that the western U.S. became wetter during glacial periods due to a southward-shifted North American storm track in response to Laurentide Ice Sheet orography, and that former western U.S. ice caps were exceptionally sensitivity to climatic perturbation.

In the second research application, the ice sheet and climate models are used to examine coupling between the Laurentide Ice Sheet and climate during ice-age cycles.  The classic “sawtooth” pattern of global sea-level change known from climate records is reproduced by linking size of the cold air trough over eastern Canada to area of the Laurentide Ice Sheet and the magnitude of orbital insolation forcing.  Results also indicate that mechanical collapse of the Laurentide Ice Sheet (e.g. through rapid iceberg discharge) is a requisite for the deglaciation of North America.  In the absence of collapse, and with consideration of ice sheet-atmosphere feedbacks, Canada would remain glaciated to present time with an ice sheet large enough to lower global sea level 15-40 m.  These results support a hypothesis that feedbacks inherent to the Laurentide Ice Sheet drive much of the global sea-level signal during ice ages.