Moored observations of upper-ocean turbulence and polynya processes

• Main Author: Miller, Una Kim
• Format: Thesis
• Language: English
• Published: 2023
• Subjects: Oceanography; Climatology; Polynyas; Turbulence; Ocean salinity; Bottom water (Oceanography); Oceanic mixing; Antarctic; Pacific; Langmuir; Antarc*
• Online Access: https://doi.org/10.7916/ttvn-rv16

The upper ocean mediates the transfer of heat and carbon between the atmosphere and ocean interior. The study of this dynamic environment, made possible in part by long-term time series gathered from oceanographic moorings, is therefore crucial to our understanding of Earth’s climate. In this thesis, we use moored datasets from the Southeast Pacific and Southern Oceans to explore two upper-ocean processes relevant to the transfer and eventual sequestration of atmospheric heat and carbon into the deep ocean: wind-, wave-, and buoyancy-forced turbulence and the release of brine in Antarctic polynyas that drives the formation of Antarctic Bottom Water (AABW). In Chapter 1, we use measurements of turbulence kinetic energy (TKE) dissipation rate (ε) collected at 8.4 m depth on the long-established Stratus Mooring in the Southeast Pacific (20° S, 85° W) to assess the applicability of Monin-Obukhov similarity theory (MOST), Law of the Wall (LOW), and other boundary layer similarity scalings to turbulence in the upper ocean. TKE facilitates the mixing of heat, momentum, and solutes within and between the ocean and atmosphere and is generated in the upper ocean primarily by wind, waves, and buoyancy fluxes. Its production can generally be assumed to equal its dissipation, and measurements of ε therefore serve as a means for quantifying turbulence in a system. We present 9 months of ε measurements, a remarkably long time series made possible by the use of a moored pulse-coherent Acoustic Doppler Current Profiler (ADCP), a new methodology for measuring ε that uniquely allows for concurrent surface flux and wave measurements across an extensive length of time and range of conditions. We find that turbulence regimes are quantified similarly using the classic Obukhov length scale (L_M=(u_*³)/(κ????ₒ), where u_* is ocean-side friction velocity, κ is the von Kármán constant, and B_0 is surface buoyancy flux) and the newer Langmuir stability length scale (L_L=(〖u_s u〗_*²)/B_0 , where u_s is surface Stokes drift velocity), ...