Estimation of Ice Shelf Melt Rate in the Presence of a Thermohaline Staircase

Tuesday, 16 December 2014
Satoshi Kimura, Keith W Nicholls and Emily Venables, NERC British Antarctic Survey, Cambridge, United Kingdom
We observed diffusive-convection favorable thermohaline staircases directly beneath George VI Ice Shelf, Antarctica. A thermohaline staircase is one of the most pronounced manifestations of double-diffusive convection. Cooling and freshening of the ocean by melting ice produce cool, fresh water above the warmer, saltier water, the water mass distribution favorable to a type of double-diffusive convection known as diffusive convection. While the vertical distribution of water masses can be susceptible to diffusive convection, none of the observations beneath ice shelves so far have shown signals of this process and its effect on melting ice shelves is uncertain. The melt rate of ice shelves is commonly estimated using a parameterization based on three equations model, which assumes a fully-developed, unstratified-turbulent flow over hydraulically smooth surfaces. These pre-requisites are clearly not met in the presence of a thermohaline staircase. We estimate the basal melt rate by applying an existing heat flux parameterization for diffusive convection in conjunction with our measurements of oceanic conditions at one site beneath George VI Ice Shelf. Our estimates yield a possible range of melt rates between 0.1 and 1.3 m/yr, where the observed melt rate of this site is ~1.4 m/yr. Limitations of the formulation and implications of diffusive convection beneath ice shelves are discussed.