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Bonneau, Jérémie

University of British Columbia

This thesis investigates physical oceanographic processes and ice-ocean interactions in Milne Fiord, a unique environment in the Canadian High Arctic where a floating ice shelf, a detached glacier tongue, and tidewater glacier coexist. Motivated by the importance of the ocean in modulating the retreat of ice shelves and tidewater glaciers, this research combines observations with a high-resolution realistic numerical model to study the circulation, heat fluxes, and melting dynamics in Milne Fiord. The numerical model, validated using long-term (>8 years) observational datasets, reveals that although Milne Fiord is relatively calm (currents <3 cm/s⁻¹), the ocean circulation is highly three-dimensional and unsteady. This complex circulation is characterized by three distinct modes – eddy, front, and barotropic – which alternate in response to offshore density variations in the coastal shelf current. These offshore density variations are also correlated with the upfjord oceanic heat flux throughout the fjord, except near the glacier face, where buoyancy forcing (freshwater input from direct submarine melt and subglacial discharge) controls the heat flux. Model results also indicate that submarine melting beneath Milne Ice Shelf is limited and that surface ablation is more significant, except near the calving front and areas where the ice is >50 m thick. Predicted ocean warming in the region (>1°C at 200 m depth) is likely to accelerate the retreat of Milne Glacier by more than doubling the submarine melt rates at depth near the grounding line. Momentum, heat, and salt budgets, combined with observations from a basal channel under Milne Ice Shelf, enabled the estimation of the drag and heat transfer coefficients, which are critical parameters for parameterization of melt/freeze at the ice-ocean boundary. The diverging values of these coefficients compared to previous studies are attributed to the observed high ice roughness, strong density stratification and frazil ice formation inside the basal channel. These findings contribute to our understanding of glacial fjords and ice shelf cavities from fine- (∼10 cm) to meso-scales (∼100 km). Advancements in this field are essential to better predict the fate of tidewater glaciers and ice shelves, which is intimately linked to sea level rise.

Text

2025-04-22

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/90714

Civil Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/