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Marine IS Instability (Ice shelf thinning (Grounding zone speedup can…
Marine IS Instability
Ice
shelves
spread out under own weight
anchored @ grounding zone
Force from anchoring
dictates speed in grounding zone
i.e. deeper g.l. --> faster grounding zone (more ice flux)
Grounding
zone retreats
If ice sheet fails to provide flux to grounding zone (Qint)
Required to balance outflux (Qgl) associated w/flow velocity
If bed = foredeepened
if bed deepens inland (as in all marine IS)
grounding zone = deeper following retreat
∴ even greater imbalance --> unstable
Thought to occur on paleo timescales
Happens so slowly - is imperceptible & hard to prove
(geological time periods)
Could raise sealevel tens metres over next hundred years
Ice Sheet on foredeepened bed
= more sensitive to condition change
Ice shelf thinning
Grounding zone speedup can drive retreat of grounding line
= induced by increased 'pulling' at g.l. by ice shelf
Problem: force should depend on g.l. depth only
regardless of ice shelf thickness
Enter: geographical setting
i.e. ice shelf 'yanks' on grounded ice