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Modelling Ice-Shelf/Ocean Interaction


Galton-Fenzi, B, Modelling Ice-Shelf/Ocean Interaction (2009) [PhD]


The effect of climate change on the mass balance of ice shelves and bottom water formation is investigated using a terrain-following three-dimensional numerical ocean model. The Regional Ocean Modeling System was modified to simulate the thermodynamic processes beneath ice shelves, including direct basal processes and frazil ice dynamics. Process-orientated studies of simplified ice-shelf-ocean cavities investigate the sensitivity of the melting/freezing to the various parametrisations which describe the internal physics of the models. The Amery Ice Shelf/ocean model is forced with tides, seasonal winds and relaxation to seasonal lateral boundary climatologies. The open ocean surface fluxes are modified by an imposed climatological sea-ice cover that includes the seasonal effect of polynyas.

The circulation and basal melting and freezing show good agreement with glaciological and oceanographic observations that have been collected from beneath the Amery Ice Shelf via boreholes through the ice and in the adjacent area of Prydz Bay. Strong horizontal and thermohaline ("ice-pump") circulation is primarily driven by melting and refreezing of the ice shelf. The net basal melt rate is ~ 45 Gt year−1 (~ 0.7 m year−1), which represents 67 % of the total mass loss of the Amery Ice Shelf. The total amount of refreezing is ~ 5.3 Gt year−1, of which 70 % is due to frazil accretion. The seasonal variability of the basal melt/freeze (up to 1 m year−1) within 100 km of the open ocean is the same magnitude as the area-averaged melt rates. The annual averaged bottom water formation rates are ~1.2 Sv to the west of the Amery, in the vicinity of Cape Darnley.

The Amery Ice Shelf/ocean model is used to investigate the sensitivity of the basal melt/freeze and bottom water formation to the inclusion of various physical mechanisms and changes in forcing. Direct comparison with glaciological observations shows that ice-shelf models that include frazil processes improve the simulated pattern of marine ice accretion. Simulations without ice-shelf/ocean thermodynamic processes overestimate bottom water formation by up to 2.8 times as much as simulations with ice-shelf/ocean thermodynamic processes, due to the missing buoyant freshwater from the melting ice shelf. Climate change sensitivity studies suggest that an ocean warming of 1C above present day temperatures can potentially remove the Amery Ice Shelf in ~500 years, solely due to increased basal melting, and can also lead to a significant decrease in the formation of bottom water. This research contributes to understanding how interaction between ice shelves and various forcing mechanisms can lead to changes in basal melt/freeze and dense water formation, which has major implications for the stability of ice shelves, sea level rise, and the salt budget of the global oceans.

Item Details

Item Type:PhD
Research Division:Earth Sciences
Research Group:Oceanography
Research Field:Physical oceanography
Objective Division:Environmental Management
Objective Group:Management of Antarctic and Southern Ocean environments
Objective Field:Antarctic and Southern Ocean oceanic processes
UTAS Author:Galton-Fenzi, B (Dr Ben Galton-Fenzi)
ID Code:71235
Year Published:2009
Deposited By:Research Division
Deposited On:2011-07-11
Last Modified:2011-07-11

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