The Dynamic Interplay of Ice Mélange and Calving Glacier Interfaces
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Rashed, Ziad
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Abstract
Future sea level projections are subject to uncertainties in ice sheet processes, including slow variations in ice flow speed and fast variations in melting and calving, which are driven by increasing oceanic and atmospheric temperatures. Recent studies suggest that the contribution of ice sheets to sea level rise over coming centuries is likely to be higher than previously projected due to the potential for rapid ice fracture and iceberg calving from the edge of ice sheets. This thesis seeks to address this issue by investigating the dynamic feedbacks between glaciers and the icebergs they generate through calving, with a particular emphasis on the role of ice mélange. Ice mélange is a slushy amalgamation of icebergs and sea ice, which is thought to function like an ice shelf by slowing glacier flow from the ice sheet interior and preventing fracturing and calving of new icebergs. Although mélange currently persists seasonally or throughout the year at numerous glaciers in Greenland and Antarctica, its importance may rise in conjunction with escalated calving rates. The principal aim of this research is to resolve open scientific questions concerning the role of ice mélange in the mechanics of iceberg calving and the retreat of glaciers.
In the first project described in this thesis, I employ the Helsinki Discrete Element Model (HiDEM) to simulate calving-mélange feedbacks down to spatial scales of meters and temporal scales of seconds. This high-fidelity model facilitates understanding of how mélange buttressing influences the stress state at the glacier terminus and enables the identification of variations in calving rates and styles. I analyze bulk calving statistics from this model, including calving event size and recurrence time, which provide insights into short time-scale events that regulate glacier calving. Though such a high-fidelity model is useful for conducting process studies of glacier calving, its high computational expense prevent its use for projecting ice sheet behavior over climate-relevant time scales of decades and longer. Consequently, I conduct a case study of Sermeq Kujalleq, the fastest flowing glacier in Greenland, using the Ice-Sheet and Sea-Level System Model (ISSM) to discern the relative impacts of submarine melting and a weakened ice mélange on the glacier's recent retreat. By adjusting the sensitivity of melt rates and a calving stress threshold parameter, I conclude that Sermeq Kujalleq's ocean-induced retreat starting in the late 1990's was predominantly driven by a weakened ice mélange following an influx of warm ocean waters. However, parameterized representation of mélange variations hinder the ability of such models to project future coupled evolution of mélange and glacier calving. To remedy this shortcoming of current models, I develop a two-dimensional continuum model of ice mélange, GLACIOME2D, which integrates the granular physics of mélange and its mechanical interactions with the ice-ocean environment over climate-relevant timescales. Collectively, my findings integrate insights from high-fidelity discrete element modeling with efficient continuum modeling to provide advances in long-term projections of ice sheet mass loss and contributions to sea level rise.
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Date
2025-12
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Dissertation (PhD)