Filling in the Map: Understanding Arctic Ocean mixing rates, mechanisms and space-time geography from ocean observations

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• Stephanie Waterman, Department of Earth, Ocean & Atmospheric Sciences, University of British Columbia
• Monday 23 January 2023, 13:00-14:00
• MR5, CMS.

If you have a question about this talk, please contact Prof. John R. Taylor.

The rates and mechanisms of ocean mixing are important controls on how the oceans function; yet, our understanding of mixing in the ocean is significantly limited by complex variability in mixing rates and processes, and by a scarcity of direct observations. In the Arctic Ocean, the challenges of understanding ocean mixing are significant: mixing measurements are especially sparse, and latitude, ice, and stratification make the mixing environment unique.

In this talk, I’ll discuss our group’s work that uses a variety of pan-Arctic observations and observational methods to better understand Arctic Ocean mixing rates, mechanisms, and space-time geography. Specifically, I will consolidate results from different studies to provide statistical characterizations of Arctic Ocean mixing rate and mixing flux distributions in time and space over a range of scales, as well as insights into the mechanisms driving and/or modulating the observed mixing space-time geography.

Our results show that turbulence and mixing in the Arctic Ocean is highly variable in space and time over a large range of scales; despite this, there are large-scale spatial and temporal patterns that relate to forcing fields. They also show that in the ocean interior, stratification typically inhibits turbulent overturning, but rare cases where and when it does not can be dominant in setting net mixing fluxes. Finally, they suggest that mixing fluxes in the central Arctic have increased over the past two decades, underpinned by stronger and more prevalent internal wave-driven mixing in summer in more recent years.

I will use this opportunity to also present some thought-provoking observations in attempts to enlist the interest of observationalists and theoreticians alike. First, I’ll show that turbulence in the Arctic Ocean interior appears to frequently be in a buoyancy-controlled regime, thus requiring an appropriate mixing efficiency to translate turbulent dissipation to diapycnal diffusivity. Next, I’ll show that in laminar and very weakly turbulent conditions in the Arctic halocline, the mixing of heat can be significantly enhanced above theoretical expectations. Finally, I’ll suggest that the prevalence of different mixing processes sets the dominant large-scale patterns of the pan-Arctic map of average effective diffusivity, with the competing stabilizing vs. destabilizing effects of double-diffusive vs. turbulent mixing processes potentially being an important control on stratification in the Arctic Ocean interior.

This talk is part of the Quantitative Climate and Environmental Science Seminars series.

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