HR: 0800h
AN: C41C-0213    [Abstracts]
TI: Internal Melt of Ridge Keels
AU: * Amundrud, T
EM: trish@eos.ubc.ca
AF: Department of Earth and Ocean Sciences University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AU: Melling, H
EM: mellingh@dfo-mpo.gc.ca
AF: Institute of Ocean Sciences Department of Fisheries and Oceans, 9860 West Saanich Road P.O. Box 6000, Sidney, BC V8L 4B2 Canada
AU: Ingram, G
EM: gingram@eos.ubc.ca
AF: Department of Earth and Ocean Sciences University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AB: Ridged ice forms a large fraction of the total volume of pack ice in the Arctic Ocean. Therefore, a realistic parameterization of the physical processes maintaining ice ridges is essential for accurate modelling of pack-ice evolution. However, the deterioration of ice ridges by melting is poorly understood. Observations of ridged sea ice during the melt season reveal that the thinning of ridges is much more rapid than the melt of surrounding level ice. We suggest that this enhanced melt is associated with the porous structure of the ridges, which allows warm oceanic water to penetrate the ridge permitting melting over a very large surface area relative to volume. To explore the effect of internal melt on ridges, a simple model of porous flow through the keel and the accompanying heat transfer has been developed. Using observations of pack-ice draft in the Beaufort Sea, a draft-dependent melt rate for a population of ice ridges can been calculated based on upper ocean temperature, relative ice-ocean velocity and geometrical parameters of idealized ridges. Predicted internal melt rates may be an order of magnitude greater than that of level ice and are found to dominate the loss of ice volume through ablation. The estimated rate of ridge deterioration using this model is comparable to the rate of ablation derived from observations of ice draft ablation by moored ice-profiling sonar. A model for ice-draft redistribution has been configured to simulate local conditions in the Beaufort Sea where data on ice draft are available. Running the model with and without internal melt has demonstrated that the porous flow through ridged ice and accompanying heat transfer can account for the enhanced rates of melt that are observed. Simulations that do not incorporate the internal melting of keels greatly overestimate the volume of the thick ice. Internal melt of ridged ice is thus an important element in the continual re-distribution of pack-ice volume. Important factors include the temperature of under-ice boundary layer and the size and packing of the blocks that form ridge keels. Clearly, accurate simulation of ridge melt processes will require more detailed information about the ice cover and ocean boundary layer than has been previously thought necessary.
DE: 4207 Arctic and Antarctic oceanography
DE: 4540 Ice mechanics and air/sea/ice exchange processes
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting