What is the role of staircase and staircase-like structures in setting heat and buoyancy fluxes from the Atlantic Water layer on a pan-Arctic scale?

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• Stephanie Waterman (University of British Columbia)
• Wednesday 22 May 2024, 11:30-12:00
• Seminar Room 1, Newton Institute.

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ADIW03 - Climate Applications of Layering

Stephanie Waterman1, Hayley Dosser2, Melanie Chanona1, Nicole Shibley3 and Mary-Louise Timmermans4 1The University of British Columbia; 2Institute of Ocean Sciences; 3Princeton University; 4Yale University Quantifying ocean mixing rates in the Arctic Ocean is critical to our ability to understand upwards oceanic heat flux, freshwater distribution, and circulation. The presence of sea ice, the high latitude, and distinct density stratification structure, with warm water underlying cooler water, all make the Arctic Ocean mixing environment unique: the Arctic Ocean exhibits a variety of mixing processes as a consequence. Low turbulence levels in the deep basins allow for the persistence of double-diffusive staircases in the upper Atlantic Water thermocline; double-diffusive fluxes associated with these staircases are the main mechanism for vertical heat transport from the warm Atlantic Water where and when staircases are present. Further, double diffusive fluxes associated with staircase structures make a unique contribution to the competition between mixing and stratification, owing to their tendency to flux buoyancy up-gradient and re-stratify the water column. In this way, they may be a critical mechanism to maintain the Atlantic Water thermocline stratification. In this work, we use year-round observations from Ice-Tethered Profilers and an archived record of ship-based measurements to: 1. characterize the prevalence of select mixing regimes, including double diffusion, internal wave breaking and non-turbulent mixing processes, in the Atlantic Water thermocline on a pan-Arctic scale; and 2. quantify the relative contribution of select mixing regimes to net heat and buoyancy transports from the Atlantic Water layer. Our results detail important regional differences in the prevalence of different mixing regimes and the significance of their relative contributions. Further, they highlight the tight competition between the de-stratifying effects of internal wave-driven mixing and the re-stratifying effects of double diffusion in the Amerasian Basin. Finally, they expose an important need to better understand mixing in the so-called transitional regime, a regime in which staircase-like features are partially-formed, disrupted, or eroded, to obtain a full description of the mixing of Atlantic Water heat and buoyancy.

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