Modelling ice-ocean interactions in and around ice shelves
File(s)
Author(s)
Jordan, James
Type
Thesis
Abstract
Physical processes in Antarctica and the Southern Ocean are of great importance
to the global climate system. This thesis considers two such processes, namely ice-
ocean interaction in ice shelf basal crevasses and the conditional instability of frazil
ice growth.
It has been suggested that freezing within basal crevasses can act as a stabilising
in
uence on ice shelves, preventing their break up. Using Fluidity, a nite element
ocean model, it is found that ocean circulation within a crevasse is highly dependent
upon the amount of freezing in the crevasse. It is also found that frazil ice formation
is responsible for the vast majority of freezing within a crevasse, and that there is
a non linear relationship between the amount of supercooling in a crevasse and its
freeze rate.
The conditional instability of frazil ice growth is a little investigated mechanism of
ice growth. Any frazil forming in the water column reduces the bulk density of a
parcel of frazil-seawater mixture, causing it to rise. Due to the pressure-decrease in
the freezing point, this causes more frazil to form, causing the parcel to accelerate,
and so on. Numerical modelling nds that the instability does not operate in the
presence of strong strati cation, high thermal driving (warm water), a small initial
perturbation, high `background' mixing or the prevalence of large frazil ice crystals.
Given a large enough initial perturbation this instability could allow signi cant rates
of ice growth even in water that is above the freezing point.
The research presented in this thesis forms the material for two peer-reviewed publi-
cations; `Modelling ice ocean interactions in ice shelf basal crevasses' (Jordan et al.,
2014) and `On the conditional frazil ice instability in seawater' (Jordan et al., 2015)
to the global climate system. This thesis considers two such processes, namely ice-
ocean interaction in ice shelf basal crevasses and the conditional instability of frazil
ice growth.
It has been suggested that freezing within basal crevasses can act as a stabilising
in
uence on ice shelves, preventing their break up. Using Fluidity, a nite element
ocean model, it is found that ocean circulation within a crevasse is highly dependent
upon the amount of freezing in the crevasse. It is also found that frazil ice formation
is responsible for the vast majority of freezing within a crevasse, and that there is
a non linear relationship between the amount of supercooling in a crevasse and its
freeze rate.
The conditional instability of frazil ice growth is a little investigated mechanism of
ice growth. Any frazil forming in the water column reduces the bulk density of a
parcel of frazil-seawater mixture, causing it to rise. Due to the pressure-decrease in
the freezing point, this causes more frazil to form, causing the parcel to accelerate,
and so on. Numerical modelling nds that the instability does not operate in the
presence of strong strati cation, high thermal driving (warm water), a small initial
perturbation, high `background' mixing or the prevalence of large frazil ice crystals.
Given a large enough initial perturbation this instability could allow signi cant rates
of ice growth even in water that is above the freezing point.
The research presented in this thesis forms the material for two peer-reviewed publi-
cations; `Modelling ice ocean interactions in ice shelf basal crevasses' (Jordan et al.,
2014) and `On the conditional frazil ice instability in seawater' (Jordan et al., 2015)
Version
Open Access
Date Issued
2014-12
Date Awarded
2015-11
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Piggott, Matthew
Sponsor
Natural Environment Research Council (Great Britain)
Publisher Department
Earth Science & Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)