Ice shelves Flashcards
(20 cards)
What determines the location of the grounding line?
The reason the grounding line is where it is, here is because the ice sheet is thick enough to push the sea water out of the way and heavy enough not to float
When thinning occurs on the ice sheet, it can reach the point where it’s not heavy enough not to float
The thickness of the ice sheet needs to be 1.1 x the height between the bed and sea level
What sets the ice shelf speed
Ice shelves are in tension everywhere, as its weight is pulling it away from the grounding line. The tension results in stretching.
Stretching rate –> increases with thickness
Velocity –> increases with stretching rate
Speeds are fastest where ice is thin and flat
How is the driving stress of the ice shelf supported?
In the case of ice shelves, the basal stress, at the bed behind the grounding line supports all the driving stress from the ice shelf
How does ocean depth influence pulling force of ice shelf at the grounding line?
The deeper the grounding line the faster the flow just upstream of the grounding line
How does the grounding zone behave in relation to the interior?
If the Flux at the grounding line is high than that in the interior, the grounding zone will thin and the grounding line will move (and vice versa)
Explain marine ice sheet instability
If the grounding line retreats to an area where the bed it deeper, as a result of the topography of the ground, the ground flux would have to increase as the deeper the grounding line, the faster the flow in the grounding zone
The interior flux is then affected by the change in flux in the grounding zone
This creates an imbalance which then leads to dynamic thinning and a retreat of the grounding line
The grounding line can retreat to deeper bed and continue a positive feedback loop leading to instability
How does buttressing influence driving stress felt at the grounding zone?
It reduces it.
What happens when buttressed ice shelves thin from melting
When ice shelves are buttressed, thinning of the ice shelf from melting, leads to faster ground flow and grounding line retreat.
Where is PIG’s buttressing most susceptible to melt than elsewhere (it’s weak points)
the shear margin
Where is buttressing most susceptible to melt than elsewhere (it’s weak points) on Smith Glacier, Thwaites?
at the boundary between the ice shelves
What did the collapse of the Larsen C ice shelf tell us about buttressing?
A lot of glaciers were flowing into Larsen B. When it collapsed, these sped up 4 fold over 2 years. Those that flowed into the remnant Larsen B, did not speed up.
This proved ice buttressing was a thing that can be observed, as until that point it had only been speculated
What is the main weakness of the marine ice cliff instability theory put forward by Deconto and pollard?
It did not take into account the influence of dynamic thinning and speed increase, which act against calving.
What are the largest ice shelves in Antarctica?
Ross and Ronne-Filchner
How is ice discharge at the grounding line calculated?
Ice discharge (at grounding line) is calculated using the velocity, thickness and width of sector
Which glacier is the highest contributor to cumulative discharge in Greenland?
Jakobshaven - contributing around 20%
Where is the velocity highest on ocean terminating glaciers?
At the front, it decreases as you go inland
What does an acceleration of ice flux lead to?
Dynamic thinning
How do you detect grounding line retreat?
You look at the ice that reacts to tides, this is how you differentiate grounded ice from floating ice through looking at elevation fluctuations using SAR interferograms
What do buttressed ice shelves help prevent?
The outflow of upstream grounded ice
