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Coupled ocean/sea-ice modelling in the Southern Ocean


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Marsland, SJ 1999 , 'Coupled ocean/sea-ice modelling in the Southern Ocean', PhD thesis, University of Tasmania.

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The ocean/sea-ice interaction in the Southern Ocean is investigated using
the Hamburg Ocean Primitive Equation Model (HOPE). The ocean
model is three dimensional and prognostically calculates velocity, temperature,
salinity and sea-surface elevation on a multi-level staggered Arakawa
E-grid. Coupled to this is a thermodynamic model of sea-ice growth and
melt, and a dynamic model with viscous-plastic rheology. Two versions have
been formulated: a high-resolution re-entrant channel model of the East
Antarctic coastline; and a medium-resolution southern hemisphere model.
In the high-resolution model the mean annual oceanic heat flux (OHF)
to the sea-ice (8 W m -2 ) is dominated by convection. There is considerable
seasonal variability in the OHF, with areal-averaged values approaching
20 W m-2in winter, and falling below 5 W M-2 in summer. There
is also considerable spatial variability in the OHF: near the sea-ice edge
mean monthly values can be above 100 W m -2; within a coastal polynya,
where the maximum annual in situ sea-ice growth is 15 m, values approach
50 W m-2; in the seasonal zone (62-64°S) an OHF in the range 5-20 W m -2
is common in the winter months; but for most of the year at most other
locations the oceanic heat flux lies in the range of 0-5 W m-2 . Sensitivities
to the magnitudes of sea-ice salinity and precipitation minus evaporation
(P-E) are investigated. The model is found to be very sensitive to processes
that affect the sea surface salinity, which determines the vertical stability of
the ocean. In turn this controls the rate of convection, and consequently the
sea-ice thickness. For the extreme case of zero P-E the model enters into
a mode of temperature-driven deep convection, characterised by relatively
warm sea surface temperature and a total collapse of the seasonal sea-ice
cycle. The medium-resolution version is used to investigate the response of
the coupled ocean/sea-ice system to a number of surface fresh water flux (SFWF) climatologies, and to changes in the mean surface air temperature
in the southern hemisphere. As with the high-resolution model the seaice
is very sensitive to the SFWF. In particular, the occurrence of a large
scale polynya in the Weddell Sea is found to depend critically on there
being a sufficient SFWF. The mean annual OHF for the Southern Ocean is
found to be around 25 W m -2 , also with considerable seasonal and spatial
variability. Increasing the SFWF by 10 cm a-1results in a decrease of 10%
in the OHF, while increasing the surface air temperature by 2°C increases
the OHF by 10%. The increase in surface air temperature results in a
decrease in mean annual sea-ice extent and volume of around 20%, while
the increase in SFWF results in an increase in mean annual sea-ice extent
of around 5%, and an increase in mean annual sea-ice thickness of around

Item Type: Thesis - PhD
Authors/Creators:Marsland, SJ
Keywords: Ocean-atmosphere interaction, Convection (Oceanography), Ocean circulation, Sea ice
Copyright Holders: The Author
Copyright Information:

Copyright 1999 the author

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1999. Includes bibliographical references

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