Constraining the Asthenospheric Viscosity Using Observations of Relative Sea Level Change Associated With the Glacial Isostatic Adjustment Process

Biassey-Bogart, Sedinam

Undergraduate Honors Thesis

Constraining the Asthenospheric Viscosity Using Observations of Relative Sea Level Change Associated With the Glacial Isostatic Adjustment Process Public Deposited

Analytics

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/r207tr03c

Abstract

Glacial Isostatic Adjustment (GIA) refers to the solid Earth’s response (i.e., surface uplift and subsi- dence) to the growth and decay of ice sheets, which is directly linked to variations in sea level. Large amounts of water can be stored on the continents as ice. When ice sheets decay or melt, the water returns to the oceans, causing sea levels to rise. Some areas experience crustal uplift due to the melting of ice sheets, and this causes sea levels to fall.

Observations of plate tectonics and seismology have provided compelling evidence for the existence of the asthenosphere, which is the mechanically weak and ductile portion of Earth’s upper mantle beneath the lithosphere. The asthenosphere is recognized as significant in Earth dynamics, yet most recent GIA models overlook its influence when predicting relative sea level change. Global sea levels are therefore affected by the volume of glacial ice on land as well as the shape of the sea floor due to tectonic activities such as uplift and subsidence.

We use analytic GIA models to compute the Earth’s viscoelastic response to loading and unloading of ice sheets. We seek to investigate how the asthenosphere influences predictions of relative sea level change at sites in North America, Fennoscandia, and in the Oceanic Islands. We do this by using different combinations of asthenosphere and lower mantle viscosities coupled with two ice models to predict relative sea level change. We then compare the model predictions to observed data of relative sea level change, thus placing constraints on the mantle viscosity structure.

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