4.7 Article

Sub-Ice Platelet Layer Physics: Insights From a Mushy-Layer Sea Ice Model

Journal

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
Volume 126, Issue 6, Pages -

Publisher

AMER GEOPHYSICAL UNION
DOI: 10.1029/2019JC015918

Keywords

Antarctic sea ice; mushy layer; platelet ice; ice shelf-ocean interaction; sea ice properties; sea ice simulation

Categories

Funding

  1. University of Otago
  2. JSPS [18F18794]
  3. Claude McCarthy Fellowship
  4. New Zealand Foundation for Research Science and Technology [IPY UOOX0705]
  5. Ministry of Business, Innovation and Employment [C01X1226]
  6. NIWA [CAOA1703]
  7. Velodrome of Roubaix
  8. Deep South National Science Challenge project, Targeted observations and process-informed modeling of Antarctic sea ice
  9. New Zealand Ministry of Business, Innovation & Employment (MBIE) [C01X1226] Funding Source: New Zealand Ministry of Business, Innovation & Employment (MBIE)
  10. Grants-in-Aid for Scientific Research [18F18794] Funding Source: KAKEN

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This study describes the halo-thermodynamic mechanisms driving the development and stability of the sub-ice platelet layer (SIPL) near Antarctic ice shelves. Through sea ice model simulations, the researchers were able to predict a realistic model analogue for the SIPL by imposing a large initial brine fraction on newly forming ice and utilizing brine rejection via advective desalination. The favorable conditions for SIPL formation include cold air, supercooled waters, and thick enough ice and snow to provide sufficient thermal insulation.
The sub-ice platelet layer (SIPL) is a highly porous, isothermal, friable layer of ice crystals and saltwater, that can develop to several meters in thickness under consolidated sea ice near Antarctic ice shelves. While the SIPL has been comprehensively described, details of its physics are rather poorly understood. In this contribution we describe the halo-thermodynamic mechanisms driving the development and stability of the SIPL in mushy-layer sea ice model simulations, forced by thermal atmospheric and oceanic conditions in McMurdo Sound, Ross Sea, Antarctica. The novelty of these simulations is that they predict a realistic model analogue for the SIPL. Two aspects of the model are essential: (a) a large initial brine fraction is imposed on newly forming ice, and (b) brine rejection via advective desalination. The SIPL appears once conductive heat fluxes become insufficient to remove latent heat required to freeze the highly porous new ice. Favorable conditions for SIPL formation include cold air, supercooled waters, and consolidated ice and snow that are thick enough to provide sufficient thermal insulation. Thermohaline properties resulting from large liquid fractions stabilize the SIPL, in particular a low thermal diffusivity. Intense convection within the isothermal SIPL generates the SIPL-consolidated ice contrast without transporting heat. Using standard physical constants and free parameters, the model successfully predicts the SIPL and consolidated ice thicknesses at six locations. While most simulations were performed with 50 layers, an SIPL emerged with moderate accuracy in thickness for three layers proving a low-cost representation of the SIPL in large-scale climate models.

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