The Arctic is warming rapidly, and its hydrological systems are evolving in response. The Mackenzie River, as the largest North American freshwater source to the Arctic Ocean, plays a critical role in the Canadian Basin’s freshwater and heat budgets. This dissertation examines the Mackenzie River’s influence through three interconnected studies. First, using five decades of observations and 21st-century climate model projections, we assess trends in river discharge, water temperature, and heat flux. Observed spring flow has increased and the annual peak discharge has shifted earlier, while river water temperatures in late summer increased, doubling the river’s September heat input to the Arctic Ocean. Under a high emission climate scenario, further warming of up to 8°C in spring water temperatures is projected by 2100, potentially tripling the river’s heat delivery and reinforcing delays in autumn sea ice formation. Second, we analyze high-resolution ocean reanalysis data (1993 - 2016) to quantify how the Mackenzie Delta’s complex channel network partitions freshwater into the Beaufort shelf. Around 75 - 80% of the river’s flow exits through western distributaries, and although total freshwater export shows a slight decline over the study period, the heat carried by the river has increased substantially. These changing fluxes have led to earlier spring ice breakup and diminished summer sea-ice cover in the delta and coastal Beaufort Sea. Third, we investigate freshwater pathways within the Arctic Ocean’s Canadian Basin using ocean reanalysis and Lagrangian particle tracking. The Beaufort Gyre has been accumulating freshwater since the 1990s under predominantly anticyclonic wind regimes, with an exceptional influx in 2007 - 2008. During that period, an unusually strong anticyclonic circulation, combined with anomalously high Mackenzie discharge and Pacific (Bering Strait) inflow, drove a pulse of fresh water into the gyre, causing record freshening observed by moorings. Lagrangian experiments confirm that Mackenzie River outflow constitutes a significant portion of the Beaufort Gyre’s freshwater, especially during such episodic events. Collectively, these findings highlight the far-reaching impact of a changing Mackenzie River on Arctic Ocean stratification and sea-ice conditions, highlighting the importance of integrating evolving river inputs into future Arctic climate assessments.
Marie Catherine McCrary (Thu,) studied this question.