香蕉视频

Please join us as we welcome Dr. Satoshi Kimura, a聽 numerical modeler from from the British Antarctic Survey for his seminar titled "Estimation of ice shelf melt rate in the presence of a thermohaline staircase". Refreshments will be served.

Abstract

Ice shelves are floating extensions of ice sheets that form along the coastal margins where the ice sheets are not thick enough to maintain contact with a bed. Thinning of ice shelves reduces the basal and lateral drags of outlet glaciers, cause an acceleration of the seaward flow of the ice sheets upstream and change the ice sheet鈥檚 contribution to the sea-level rise. Oceanic conditions beneath the ice shelves are isolated from the atmospheric forcing by ice (typically between 100 and 2000 m thick), and the major forcing is the phase change at the ice-shelf base. We observed 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 produces cool, freshwater above the warmer, saltier water, the water mass distribution favourable 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 a three-equation model, which assumes a fully developed, unstratified turbulent flow over hydraulically smooth surfaces. These prerequisites are clearly not met in the presence of a thermohaline staircase.聽 I will discuss an approach to estimate the basal melt rate by applying an existing heat flux parameterization for diffusive convection in conjunction with the measurements of oceanic conditions at one site beneath George VI Ice Shelf.