Densification and Recrystallization of Firn at Dome C, Central East Antarctica
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Date
1980-06
Authors
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Journal ISSN
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Publisher
The Ohio State University
Abstract
A study of variations of density,
crystal size, and crystal shape with depth to
50 m depth for Dome C, central East Antarctica,
is reported.
The critical point in the depth-density
profile is less sharply defined than at many
locations. Benson's model for variation of
pore space with depth provides an adequate, but
not perfect, description of the observed behavior.
An empirical relation discovered by Gow for
dependence of depth-density profiles on temperature
and accumulation cannot be extended to
the low-temperature, low-accumulation conditions
of Dome C.
The observed profile differs from log-linear
densification expected for unconfined sintering
of ceramics in a manner which is explicable if
load has an important effect on densification.
The relative behavior of the Dome C and South Pole
age-density profiles also shows that load is an
important parameter in firn densification.
The core consists of dense, fine-grained
wind crusts contained in more-extensive, less-dense,
coarse-grained firn. Density ranges
between superjacent coarse and fine layers
decrease exponentially with depth. Lower rates
of densification are observed for fine-grained
firn because such firn has greater area of grain
boundary per unit volume than coarse firn, and so
resists deformation under load better. A simple
unconfined-sintering model for densification
predicts more rapid densification of fine firn,
and thus is shown to have limited applicability.
Load and mean annual temperature are probably
the controlling factors in firn densification
between 5 m and 50 m depth.
The rate of growth of crystals in fine layers
is almost three times that of crystals in coarse
layers. The rate of growth of coarse crystals
agrees well with that predicted by Gow. Variations
in crystal sphericity, internal free surface, and
crystal boundary area with depth reveal that coarse-grained
firn consists of several genetically-different
types of firn.
Thin sections of firn may be prepared using
the nontoxic chemical dodecane as a filler. To
determine mean crystal area in a section, the 50
largest crystals following the 5 largest crystals
should be measured, such that about 25% of the
crystals in a section are measured.