From the Subglacial Environment to the Coastal Ocean: Exploring Feedbacks Between Glacial Meltwater and Tidewater Glacier Dynamics.
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Date
2023-03-24
Authors
Hager, Alexander
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Publisher
University of Oregon
Abstract
Mass loss from the Antarctic and Greenland ice sheets has accelerated in recent decades and is predicted to contribute < 40 cm of mean sea level rise in the 21st Century. However, there is significant uncertainty in projections of ice sheet mass balance arising from unknowns in the dynamic response of tidewater glaciers to ocean forcing. At both the ice-ocean and ice-bed boundaries, glacial meltwater plays a vital role in governing the dynamics of tidewater glaciers, yet many meltwater processes are difficult to observe and are subsequently parameterized with unvalidated approximations in ice sheet models. Here, I employ a suite of numerical modeling experiments and observations to investigate how glacial meltwater at the bed and in the ocean affects the susceptibility of tidewater glaciers in Antarctica, Alaska, and Greenland to enhanced ocean forcing.
It has historically been assumed that the formation of channelized subglacial drainage beneath Antarctic ice sheets is not possible, leading to the use of simplifying parameterizations of subglacial drainage under Antarctic ice sheets. However, recent observations have suggested subglacial channels exist beneath some Antarctic tidewater glaciers and could have a substantial impact on ice shelf ablation and glacier dynamics. In Chapter II, I pair numerical modeling experiments with observed radar specularity content from Thwaites Glacier, West Antarctica, to demonstrate that enough basal meltwater exists to form subglacial channels, which increase frontal ablation and basal friction beneath Thwaites Glacier.
In Chapter III and IV, I transition to investigating the impact of glacial meltwater on glacial fjord dynamics. Leveraging numerical modeling with hydrographic observations from LeConte Bay, Alaska, I show that the sill-driven mixing and buoyancy forcing of subglacial discharge drives strong seasonal circulation regimes in LeConte Bay and may impede ice sheet models from accurately parameterizing ocean thermal forcing of tidewater glaciers. I then run further modeling experiments to test the accuracy ocean thermal forcing parameterizations in Greenland ice sheet models. By identifying the dominant local controls on local water transformation, I develop simple improvements to existing thermal forcing parameterizations that decrease parameterization error by < 89%.
This dissertation includes previously published and co-authored material.
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Keywords
Alaska, Antarctica, Glacial Fjords, Greenland, Ice-ocean Interactions, Tidewater Glaciers