| Summary: | My dissertation investigates the physics of double-diffusive convection, a small-scale mixing process that causes vertical heat transport from Arctic Ocean waters toward the overlying sea ice cover. This diffusive-convective mechanism is evidenced by its signature staircase, comprised of adjacent pairs of thick mixed layers and thin interfaces in temperature and salinity. The necessary temperature and salinity conditions for double-diffusive convection are prevalent in the Arctic Ocean, where cool and fresh waters sit above the warm and salty Atlantic Water Layer, whose waters have originated from the Atlantic Ocean. At the top of this Atlantic Water Layer, a double-diffusive staircase is often found. In this dissertation, I investigate the physical mechanisms which govern the vertical heat fluxes associated with these Arctic staircases, staircase temporal and spatial evolution, and the fluid dynamical processes underlying the persistence and manifestation of Arctic staircase features. A combination of analytical theory, numerical simulations, and in-situ observations are invoked to both understand the physics governing staircase properties in the Arctic Ocean, as well as to investigate how double-diffusive structures and associated vertical heat transport may be modified in a changing Arctic Ocean. Specifically, I have conducted the first Arctic-wide analysis of double-diffusive staircase properties. I use data from Ice-Tethered Profilers to explore these properties and to quantify vertical double-diffusive heat fluxes, generally of O(0.1)~Wm$^{-2}$, arising from the Arctic's warm Atlantic Water Layer. Through characterization of the double-diffusive staircase across the entire Arctic, I find evidence that staircases are absent in boundary regions, raising the idea that energetic regions of the Arctic, possibly subject to shear-driven turbulence, may lead to the disruption of the double-diffusive staircase. In the next chapter, I describe the development of a mathematical model to explore the effects of ...
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