Modeling the Vertical Structure of Ice Shelf-Ocean Boundary Current under Supercooled Condition with Suspended Frazil Ice Processes

Chen Cheng, Nanjing University of Information Science & Technology, School of Marine Sciences, Nanjing, China, Adrian Jenkins, NERC British Antarctic Survey, Cambridge, United Kingdom, Zhaomin Wang, Hohai University, Nanjing, China and Chengyan Liu, Nanjing University of Information Science and Technology, Nanjing, China
In contrast with the severe thinning of the ice shelves along the coast of west Antarctic, large ice shelves with deep grounding lines gained mass during 1994-2012. This positive mass budget is inevitably associated with the marine ice production which is originated from the supercooled Ice Shelf Water plume carrying suspended frazil ice along the ice shelf base. In addition, the outflow of this supercooled plume from beneath ice shelf arguably exerts a pronounced influence on the Antarctic Bottom Water properties and its production. However, the knowledge of this buoyant and frictional supercooled flow is still limited nowadays, let alone its vertical structure that is generally assumed to be vertically uniform. Here we extend the vertical one-dimensional model of ice shelf-ocean boundary current from Jenkins (2016) by incorporating the frazil ice module and a fairly sophisticated turbulence closure with density stratification effects. Based on this extended model, we reproduce the measured thermohaline properties of a perennially-prominent supercooled ice shelf-ocean boundary current underneath the Amery Ice Shelf, East Antarctic, and carry out extensive sensitivity runs to a wide range of factors including vertical convection, horizontal advection, far-field geostrophic currents, basal slope, roughness length, frazil ice size configuration, and turbulence closure. Based on the simulated results, following conclusions can be drawn: First, using the constant eddy viscosity/diffusivity can hardly reproduce reasonably the vertical structure of ice shelf-ocean boundary current. Second, the size of the finest ice crystals plays an important role in controlling the ice shelf-ocean boundary current. Last but more important, the ice shelf-ocean boundary layer response to the gradient of frazil ice concentration is to reduce appreciably the level of turbulence. Therefore, this study highlights the importance of strong interactions between the frazil ice formation and the hydrodynamics of ice shelf-ocean boundary layer. That should be sufficiently resolved in the existing three-dimensional ice shelf-ocean coupled models once they are applied in the cold ice cavities, with potential consequences for the overall ice shelf mass balance and Antarctic Bottom Water production.