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PIG Flow 2 (HiRes Bed vs Basal Traction (Further West (downglacier) (MUCH…
PIG Flow 2
HiRes Bed vs Basal Traction
High resolution beds (Bingham 2017)
vs model inverted basal traction (Arthern 2015)
Main trunk
Low traction modelled
Radargrams
show
flatter bed
Further West
(downglacier)
MUCH higher traction values
Radargrams
show
rougher bed
suggets
form drag
= cause of resistance
∴ Radar surveys
validate relation btwn basal traction & form drag
BEDMAP
Low resolution bed topogrpahy data
Interpolated airborne data
∴ not direct obvs
Input for current IS models
∴ Antarctic bed modelled as quite flat
--> will affect predictions
iSTAR Radar
vs BEDMAP Bed Data
BEDMAP - smooth bed
iSTAR Radar - lineated bed
BEDMAP resolution = key limitation to ice modelling
probably results in faster ice flow predictions
Sonar Imaging
Imaged shallow shelf in Pine Island Bay
= Former ice bed
Analogues for iSTAR feats
Streamlined, rocky
- Inner Pine Island Bay
Shallow lineations
- Outer Pine Island Bay
further out on shelf where lotsa seds built up by glaciers
Future Study
∴ Must develop methods
to predict/ detect where form drag = esp influential
Some surface obvs may be used to infer bed data/feats
Need better model characterisation basal traction
Radar findings
Central Trunk
Lump protudes
~300m into ice above
likely affects ice flow/resistance to ice flow
Lineations run over lump
along ice flow direction
LINEATED BED - Depositional feats ?
Eastern Tributary
Ridge sticks out
up to 50m into ice in along flow direction
Sign ice = trying to erode rocky bed?
Heightened amplitude lineations
~ immature ?
ice still trying to erode bed smooth ?
more rocky bed?
Offshore analogues support iSTAR proposal
Nearer g.l.
Rock-cored, heightened feats
Further inland
Shallow, depositional/sed
w lotsa subglacial sed
Form Drag
Form drag = controlling basal traction @ PIG
Dictating resistance @ bed ∴ ice flow
∴ Areas of high basal traction
= where large obstacles block flow/cause resistance
Form drag implications
Constant spatial resistance to flow
Basal topog feats
unlikely to move
if form drag = control
Basal traction likely constant
Whereas, if another control,
If control = subglacial sed def/basal sliding:
i.e. Sediment wetness would've dictated flow & subglacial water VARIES
Resistance to flow likely to vary
Explains Siple Coast Ice Streams ?
Tendency to migrate/shutdown/restart