Ocean mixing beneath Pine Island Glacier ice shelf, West Antarctica

Abstract

Ice shelves around Antarctica are vulnerable to an increase in ocean‐driven melting, with the melt rate depending on ocean temperature and the strength of flow inside the ice‐shelf cavities. We present measurements of velocity, temperature, salinity, turbulent kinetic energy dissipation rate, and thermal variance dissipation rate beneath Pine Island Glacier ice shelf, West Antarctica. These measurements were obtained by CTD, ADCP, and turbulence sensors mounted on an Autonomous Underwater Vehicle (AUV). The highest turbulent kinetic energy dissipation rate is found near the grounding line. The thermal variance dissipation rate increases closer to the ice‐shelf base, with a maximum value found ∼0.5 m away from the ice. The measurements of turbulent kinetic energy dissipation rate near the ice are used to estimate basal melting of the ice shelf. The dissipation‐rate‐based melt rate estimates is sensitive to the stability correction parameter in the linear approximation of universal function of the Monin‐Obukhov similarity theory for stratified boundary layers. We argue that our estimates of basal melting from dissipation rates are within a range of previous estimates of basal melting.

Turbulence Observations Beneath Larsen C Ice Shelf, Antarctica

“…In line with the increasing energy levels as a function of mean flow speed, the rate of TKE dissipation increases from a minimum of ~10 ‐9 W/kg at both MAVS to a maximum of ~10 ‐6 W/kg at the upper MAVS and ~10 ‐7 W/kg at the lower MAVS (Figures a and b). The rate of TKE dissipation is similar to that observed under sea ice in the Arctic (McPhee, ; Peterson et al, ) and the Antarctic (McPhee, ; McPhee & Martinson, ), but is greater than that observed beneath Pine Island Ice Shelf (~10 ‐9 W/kg; Kimura et al, ) and George VI Ice Shelf (~10 ‐10 W/kg; Venables et al, ). As a function of mean flow speed, ε scales as a power law at the upper MAVS ( r 2 = 0.93) and exponentially at the lower MAVS ( r 2 = 0.93).…”

“…Buoyancy effects appear to be negligible, and the input of freshwater from basal melting appears to play little role in the TKE budget. While buoyancy forces are known to be important elsewhere (e.g., beneath George VI Ice Shelf or Pine Island Ice Shelf; Kimura et al, 2015Kimura et al, , 2016Stanton et al, 2013), these locations are characterized by substantially weaker tidal forcing and lower shear production rates of TKE. Therefore, we propose that strong tidal forcing is a key factor in generating the shear-dominated regime such as that we have observed beneath Larsen C Ice Shelf.…”

Ocean Tide Influences on the Antarctic and Greenland Ice Sheets

“…Velocity sensors on autonomous underwater vehicles (AUVs) such as the UK Autosub (Jenkins et al, , ; Kimura et al, ; Nicholls et al, ) could also reveal information on the tidal contribution to currents under an ice shelf over a broader region than can be obtained from a few moorings deployed through the ice. However, explicit separation of the tidal component from the continuum of ocean current components would require long missions that return to specific locations to measure currents at carefully determined times.…”

Implementation and performance of adaptive mesh refinement in the Ice Sheet System Model (ISSM v4.14)

“…This argument is based on the results shown here, for both MISMIP3d and MISMIP+ setups. Some mesh packages and finite element libraries related to NeoPZ are Deal II (Bangerth et al, 2007), Hermes (Šolín et al, 2008), libMesh (Kirk et al, 2006) and HP90 (Demkowicz et al, 1998). Mesh generators related to Bamg are MMG (Dapogny et al, 2014), Yams (Frey, 2001) and Gmsh (Geuzaine and Remacle, 2009).…”