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Modelling ice-shelf/ocean interaction

Galton-Fenzi, BK 2009 , 'Modelling ice-shelf/ocean interaction', PhD thesis, University of Tasmania.

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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 1°C 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 Type: Thesis - PhD
Authors/Creators:Galton-Fenzi, BK
Copyright Information:

Copyright 2009 the author

Additional Information:

Thesis (PhD)--University of Tasmania, 2009. Includes bibliographical references

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