Rates and Mechanisms of Turbulent Mixing in a Coastal Embayment of the West Antarctic Peninsula

Abstract

Ice shelves in the West Antarctic sector are experiencing the greatest mass loss anywhere in Antarctica, with basal melt rates of up to ∼5 m yr −1 (Rignot et al., 2013). The melting and thinning of these floating tongues of land-based ice cause the grounded glaciers that feed them to accelerate, contributing significantly to sea level rise (Dupont & Alley, 2005;Rott et al., 2002). The West Antarctic Peninsula (WAP) also contains hundreds of marine-terminating glaciers, the majority of which are retreating, with the potential to further raise global sea level (Cook et al., 2016;Huss & Farinotti, 2014). The ice shelf and glacial melting have been attributed to an increased intrusion of warm, saline Circumpolar Deep Water (CDW), which originates in the mid-layers of the Antarctic Circumpolar Current (ACC; Cook et al., 2016;Jacobs et al., 1996). Off

Mixing and Overturning Across the Brazil‐Malvinas Confluence

“…This is more easily accomplished than directly estimating a mesoscale eddy flux and decomposing that vector field into convergent and rotational components, as the contribution to χ from eddy stirring relates to the downgradient portion of the eddy flux (see Naveira Garabato et al (2016) for further detail). The enabling of frequent and extensive high-quality microstructure sampling from autonomous platforms-such as floats (Lien et al, 2016;Roemmich et al, 2019) and gliders (Fer et al, 2014;Scott et al, 2021)-by recent technological advances opens up new opportunities to utilize our approach in addressing a range of traditionally challenging problems featuring (sub-)mesoscale eddies. Such problems include the assessment of physical exchanges across major current systems such as the ACC, or between western boundary currents and mid-ocean regions, and the export of recently ventilated waters from areas of mode water formation or deep convection sites.…”

Observations of Modified Warm Deep Water Beneath Ronne Ice Shelf, Antarctica, From an Autonomous Underwater Vehicle

“…The RSI MicroRider package had four microstructure probes sampling at a rate of 512 Hz: two orthogonally positioned shear probes that provide an estimate of the rate of turbulent kinetic energy dissipation (TKE; ε), and two thermistor probes that provide an estimate of the rate of thermal variance dissipation (χ). The microstructure data were processed following standard methods (e.g., Inall et al., 2022; Kimura et al., 2016; Piccolroaz et al., 2021; Scott et al., 2021). Under the assumption of small‐scale isotropy, ε can be estimated as $$${\varepsilon}=\frac{15}{2}\nu \left\langle {\left(\frac{{\partial u}^{\prime }}{\partial z}\right)}^{2}\right\rangle =\frac{15}{2}{\nu}\int \nolimits_{0}^{{k}_{I}}{\psi }_{S}(k)\,dk,$$$ where ν is the temperature‐dependant kinematic viscosity of seawater and $$\left\langle {\left({\partial u}^{\prime }/\partial z\right)}^{2}\right\rangle $$ is the variance of the velocity shear fluctuations perpendicular to ALR's path (Osborn, 1974) derived from integrating the velocity shear spectrum $${\psi }_{S}$$ in wavenumber space $$k$$ up to $${k}_{I}$$.…”

“…The RSI MicroRider package had four microstructure probes sampling at a rate of 512 Hz: two orthogonally positioned shear probes that provide an estimate of the rate of turbulent kinetic energy dissipation (TKE; ε), and two thermistor probes that provide an estimate of the rate of thermal variance dissipation (χ). The microstructure data were processed following standard methods (e.g., Inall et al, 2022;Kimura et al, 2016;Piccolroaz et al, 2021;Scott et al, 2021). Under the assumption of small-scale isotropy, ε can be estimated as…”

Influence of seasonally varying sea-ice concentration and subsurface ocean heat on sea-ice thickness and sea-ice seasonality for a ‘warm-shelf’ region in Antarctica

“…More generally on the WAP, other than by entrainment during brine rejection, cross-pycnocline mixing of CDW heat is believed to occur primarily through shear-driven instability (as opposed to double-diffusive convection; Howard and others, 2004; Brearley and others, 2017). Vertical heat fluxes out of the CDW layer have been estimated by combining observed temperature gradients with diffusivities estimated from parameterizations (using observations of shear and stratification; Howard and others, 2004; Brearley and others, 2017; McKee and others, 2019) or, more recently, from microstructure measurements of dissipation (Scott and others, 2021; Inall and others, 2022), and background values range from less than 1 W m −2 to about 2 W m −2 with large spreads, indicating mixing is intermittent. As for the origin of the shear, Howard and others (2004) determined that near-inertial waves were the primary source whereas Brearley and others (2017) showed the origin varies depending on the sea ice cover.…”

“…When sea ice is present, wind input is damped so that inertial waves are suppressed and tides, though weak, are the main source of shear. Other important mixing processes that drive vertical heat movement are tied to bathymetry, including mixing associated with overflows at sills by which colder pycnocline waters are entrained into the CDW (Venables and others, 2017), and hydraulic control at ridges by which persistent, larger heat fluxes (~5 Wm −2 ) can supply CDW heat to the pycnocline after which episodic wind-driven mixing can tap into it (Scott and others, 2021).…”