Zhuang, Kelin (2010-08). Occurrence and Stability of Glaciations in Geologic Time. Doctoral Dissertation. Thesis uri icon


  • Earth is characterized by episodes of glaciations and periods of minimal or no ice
    through geologic time. Using the linear energy balance model (EBM), nonlinear EBM
    with empirical ice sheet schemes, the general circulation model coupled with an ice
    sheet model, this study investigates the occurrence and stability of glaciations in
    geologic time.
    The simulations since the last glacial maximum (LGM) suggest that the summertime
    thawline of ice sheets conforms closely to the equatorward edge of the ice sheets and
    implies the relative stability toward deglaciation.
    CO2 levels are indispensable in controlling the initiation of ice sheet in the Cretaceous.
    At low CO2 levels, ice sheets exist in all periods no matter LGM or the last interglacial
    (LIG) orbital elements; however, at high CO2 levels ice sheets rarely exist.
    The simulations agree well with recent geological evidence of the hysteresis of
    glaciations in the Permo-Carboniferous. Gondwanaland reached its glacial maximum
    when CO2 level was roughly the same or slightly higher than the preindustrial value.
    With a further increase of CO2, deglaciation dominates and results in an ice free state.
    Again, if CO2 decreased to the present level, Gondwanaland would be glaciated once
    more and start a new cycle of glaciation and deglaciation.
    Simulations from five paleogeography maps in Gondwanaland with a suite of CO2 levels
    and different orbital elements reveal that paleogeography, CO2 levels and the
    Milankovitch cycles all contribute to the glaciations of Gondwanaland.
    This study shows that orbital elements alone are insufficient to account for the evolution
    of ice sheets. Net radiative forcing caused by greenhouse gases, such as CO2 and solar
    constant change are the primary drivers to glacial inception or demise. Continental
    geography, CO2 levels, solar constant change, and the Milankovitch cycles complicate
    the glacial history of Earth.

publication date

  • August 2010