Abstract
The observable microstructures in ice are the result of many dynamic and
competing processes. These processes are influenced by climate variables in
the firn. Layers deposited in different climate regimes may show variations
in fabric which can persist deep into the ice sheet; fabric may `remember'
these past climate regimes. We model the evolution of fabric variations
below the firn-ice transition and show that the addition of shear to
compressive-stress regimes preserves the modeled fabric variations longer than
compression-only regimes because shear drives a positive feedback between
crystal rotation and deformation.
Even without shear, the modeled ice retains memory of the fabric variation for
$\approx 200 \unit{ka}$ in typical polar ice-sheet conditions. Our model shows
that temperature affects how long the fabric variation is preserved, but
only affects the strain-integrated fabric evolution profile when comparing
results straddling the thermal-activation-energy threshold ($\approx
-10 \degr \unit{C}$). Even at high temperatures, migration recrystallization
doesn't eliminate the modeled fabric's memory under most conditions. High levels of
nearest-neighbor interactions will, however, eliminate the modeled fabric's memory
more quickly than low levels of nearest-neighbor interactions. Ultimately,
our model predicts that fabrics will retain memory of past climatic variations when
subject to a wide variety of conditions found in polar ice sheets.
