UVM Theses and Dissertations
Format:
Print
Author:
Graly, Joseph
Dept./Program:
Geology
Year:
2010
Degree:
MS
Abstract:
Isotopic records of glacial ice volume indicate four brief periods during the Pleistocene when global ice volume was smaller than the present minimum, indicating temperatures warmer than present. Constraining the response of Earth's ice sheets to these past warm periods aids the prediction of ice sheet response to future warming. Mathematical models of ice sheet climate response suggest that melting of the Greenland Ice Sheet may have dominated sea level increase during these Pleistocene warming events.
To directly test whether the Greenland Ice Sheet has retreated beyond its present margin, the cosmogenic isotope meteoric ¹⁰Be was measured in ice-bound fine sediment collected from three West Greenland sites. Because meteoric ¹⁰Be is formed in the atmosphere and deposited on the ice sheet during glacial periods, any substantial meteoric ¹⁰Be inventory in ice-bound sediment originates from periods when the western Greenland Ice Sheet was smaller than present. The three sites varied bllatitude from 67°N to 72.5°N. Meteoric ¹⁰Be concentrations between 2.10⁶ and 2·10⁸ atoms/g were found at the northern two sites. Significantly lower concentrations between 2·10⁶ and 5.10⁷ atoms/g were found at the southernmost site.
As this ice-bound sediment is ultimately sourced from sub-ice soils, previous studies on meteoric ¹⁰Be's distribution in soil were exhaustively compiled. The compellation demonstrates that meteoric ¹⁰Be is consistently retained in soil and that its distribution is unique and not exclusively controlled by anyone soil property. This compellation also shows that meteoric ¹⁰Be distribution with depth is sufficiently consistent to allow for the modeling of its long-term evolution and the prediction of the total inventory of meteoric ¹⁰Be in a soil profile from the soil's maximum meteoric ¹⁰Be concentration.
To translate inferred soil meteoric ¹⁰Be inventories into soil ages, short and longterm meteoric ¹⁰Be deposition rates were likewise compiled from the literature. This study finds that while short term meteoric ¹⁰Be deposition rates are predictable by latitude and precipitation within ~20%, changes in geomagnetic field, dust flux, and climate may cause long-term meteoric ¹⁰Be deposition rates to vary. Warm-period meteoric ¹⁰Be deposition rates for Greenland are best predicted from mid-Holocene values.
Based on the compiled meteoric ¹⁰Be depth distribution data and the global ice volume record, a forward model of meteoric ¹⁰Be evolution under the Greenland Ice Sheet is constructed. This model shows that the high meteoric ¹⁰Be concentrations found at the northern two sites are best explained by the slow erosion of pre-glacial regolith. The meteoric ¹⁰Be concentrations at the southern site likely developed during Pleistocene interglacial periods, and indicate that the Southern Greenland Ice Sheet leads global ice volume in warm period retreat.
To directly test whether the Greenland Ice Sheet has retreated beyond its present margin, the cosmogenic isotope meteoric ¹⁰Be was measured in ice-bound fine sediment collected from three West Greenland sites. Because meteoric ¹⁰Be is formed in the atmosphere and deposited on the ice sheet during glacial periods, any substantial meteoric ¹⁰Be inventory in ice-bound sediment originates from periods when the western Greenland Ice Sheet was smaller than present. The three sites varied bllatitude from 67°N to 72.5°N. Meteoric ¹⁰Be concentrations between 2.10⁶ and 2·10⁸ atoms/g were found at the northern two sites. Significantly lower concentrations between 2·10⁶ and 5.10⁷ atoms/g were found at the southernmost site.
As this ice-bound sediment is ultimately sourced from sub-ice soils, previous studies on meteoric ¹⁰Be's distribution in soil were exhaustively compiled. The compellation demonstrates that meteoric ¹⁰Be is consistently retained in soil and that its distribution is unique and not exclusively controlled by anyone soil property. This compellation also shows that meteoric ¹⁰Be distribution with depth is sufficiently consistent to allow for the modeling of its long-term evolution and the prediction of the total inventory of meteoric ¹⁰Be in a soil profile from the soil's maximum meteoric ¹⁰Be concentration.
To translate inferred soil meteoric ¹⁰Be inventories into soil ages, short and longterm meteoric ¹⁰Be deposition rates were likewise compiled from the literature. This study finds that while short term meteoric ¹⁰Be deposition rates are predictable by latitude and precipitation within ~20%, changes in geomagnetic field, dust flux, and climate may cause long-term meteoric ¹⁰Be deposition rates to vary. Warm-period meteoric ¹⁰Be deposition rates for Greenland are best predicted from mid-Holocene values.
Based on the compiled meteoric ¹⁰Be depth distribution data and the global ice volume record, a forward model of meteoric ¹⁰Be evolution under the Greenland Ice Sheet is constructed. This model shows that the high meteoric ¹⁰Be concentrations found at the northern two sites are best explained by the slow erosion of pre-glacial regolith. The meteoric ¹⁰Be concentrations at the southern site likely developed during Pleistocene interglacial periods, and indicate that the Southern Greenland Ice Sheet leads global ice volume in warm period retreat.