Geological Sciences Theses and Dissertations

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Browsing Geological Sciences Theses and Dissertations by Author "Abib, Nicole"

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    From Terminus to Sill: Feedbacks between Fjord Stratification, Subglacial Discharge, and Glacier Ice
    (University of Oregon, 2024-08-07) Abib, Nicole; Sutherland, David
    Mass loss from tidewater glaciers worldwide has increased in recent decades, partially attributed to changes occurring at the ice-ocean interface. The melting of the Greenland and Antarctic Ice Sheets have contributed up 14 mm of sea level rise over the past 20 years, and there remains large uncertainty into how these numbers will evolve into the future. At present, ~one-half of the ice lost annually from the Greenland Ice Sheet is due to frontal ablation, or the combination of submarine melting and iceberg calving, with similar percentages observed in Antarctica and other locations where glaciers reach the ocean. Frontal ablation changes the geometry of a glacier’s terminus, influencing glacier dynamics, the fate of upwelling plumes, and the distribution of submarine meltwater input into the ocean. Directly observing frontal ablation and terminus morphology below the waterline is difficult, however, limiting our understanding of these coupled ice-ocean processes. In this dissertation, I use both remotely sensed and field-based observations to investigate the processes that contribute to tidewater glacier evolution. In Chapter II, I combine 3-D multibeam point clouds of the subsurface ice face at LeConte Glacier, Alaska, with concurrent environmental conditions to show that the terminus morphology is predominately overcut despite high multibeam sonar-derived melt rates. This finding challenges the assumption that tidewater glacier termini are largely undercut during periods of high submarine melting and suggests that important glacier-ocean feedbacks are missing from current submarine melt rate theory. In Chapter III and IV, I examine one currently understudied piece of glacial fjord dynamics – the input of meltwater from ice mélange in the upper layers of the water column. I use field observations collected before and after an ephemeral ice mélange event in front of Kangilliup Sermia, Greenland, to directly investigate the extent to which ice mélange meltwater can modify glacier-adjacent water properties. I show that ice mélange can cause substantial cooling and freshening of the water column, leading to a stratification change down to the depth of the outflowing discharge plume and substantial modification of upper layer hydrography. I then expand this analysis to a suite of glacial fjords in Central West Greenland to investigate the conditions under which ice mélange forms and dissipates, finding that for glacial fjords with a deep grounding line, ice mélange breakup date is highly correlated with subglacial discharge plume evolution. This implies that future changes to ocean stratification or subglacial discharge magnitude will alter the duration over which ice mélange is present, thereby changing the timing of its meltwater injection into the proglacial fjords on which it sits and the length of time it is able to supply buttressing force to glacier termini. This dissertation includes previously published and unpublished co-authored material.