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RAPID: Quantifying turbulent mixing and heat flux in the Mackenzie Canyon and across the Beaufort continental slope in the Arctic Ocean


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Ocean & fiord systems
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The Arctic Ocean is the one place in the world where the warm, salty waters from the Atlantic Ocean meet the colder and fresher waters of the Pacific Ocean. Because the Pacific Water is fresher, it is lighter and floats above Atlantic Water (AW), which is warm but heavy and sinks to fill the depths of the Arctic Ocean. As such, the Pacific waters act as a physical barrier that prevents warm Atlantic waters from reaching the surface where they can cause increased melting of sea ice. Because the flow of Atlantic Water is approximately ten times stronger than the flow of Pacific Water, it represents a huge potential for influencing sea ice coverage. However, because it is salty and heavy, Atlantic waters cannot reach the ocean surface unless they are actively drawn to the surface. The ocean’s tides and winds provide energy sources for lifting these heavy waters and the mechanisms for raising these waters to the surface are not well understood. This project studies how the Mackenzie Canyon - a submarine canyon - can act as a conduit to draw up the deep, warm Atlantic Water to the shallow shelves, and mix it into shallow, near-surface water masses where it may influence sea-ice processes. Redistribution of heat by turbulent mixing plays an important role in controlling the ocean climate in the Arctic. This is a unique opportunity that documents the dynamics and mechanisms during a time where ice-cover and the Arctic Ocean structure is rapidly evolving. For this project, the research team uses special custom-made mixing sensors and a commercially available acoustic instrumentation aboard an already-planned field experiment to allow characterization of the rate at which heat is being drawn to the Arctic Ocean’s surface through turbulent mixing processes. The individual processes and sources of energy responsible for this heat transfer (e.g., tides, winds, and mean flow) vary depending on how details of the forcing combine, often creating geographic hotspots of mixing that dominate the net turbulent heat fluxes. Continental slopes have been identified as one such conduit for heat. This project determines how much and by what mechanism warmer Atlantic Water (AW) is modified and upwelled due to the presence of the slope-incising topography of the Mackenzie Canyon, compared to the smoother Beaufort continental slope. Aims include providing turbulent instrumentation added to the Arctic Observing Network (AON) conductivity, temperature, and depth (CTD) survey sections to estimate turbulent dissipation rate and heat fluxes within the canyon and across the AON hydrographic transects of the Beaufort Sea, where there are relatively few known turbulence observations. As a result of this work, the project obtains a comprehensive map of the turbulent heat flux and dissipation rate across the Beaufort slope via the AON transects and within the Mackenzie Canyon. This work is important for measuring ocean dynamics and increases understanding of the influence of incising topography to the upward heat flux from the Atlantic Water in the Arctic Ocean. While canyons represent a small percentage of the coastline in the Arctic, this project’s measurements quantify their contribution to the modification and transport of heat in the Beaufort Sea. On a larger scale, this work contributes to refining methods for calculating turbulent quantities using two different CTD-mounted instruments in the Arctic, a region rich with warm lateral intrusions and significant heat flux across regions of variable and complex topography.