Ice sheets

Question 1

What is an ice sheet?

Answer 1

It is an extensive (continental scale) region of PERMANENT ice cover.

E.g. Greenland, West + East Antarctica.

Question 2

What is a marine ice sheet?

Answer 2

It is an ice sheet that is GROUNDED well BELOW sea level

E.g. West Antarctica.

Question 3

What is an ice shelf?

Answer 3

It is a thick FLOATING platform of ice fed by glaciers or ice streams.

Question 4

What are ice streams?

Answer 4

It is FAST moving ice bounded by SLOWER moving ice (apposed to a glacier that is bounded by rock).

Question 5

Sea Level Equivalence (SLE):

Ice sheets
Greenland
West Antarctica
East Antarctica

Answer 5

Ice sheets = approx 63m of SLE
Greenland = 7.3m of SLE
West Antarctica = 4.3m of SLE (marine ice sheet)
East Antarctica = 53.3m of SLE

Question 6

Does an ice sheet lose mass?

Answer 6

Yes, through:

1. Ice shelf calving (Antarctica and Greenland)
2. Melt (surface) (Greenland = a lot, Antarctica = a little),
3. Melt (sub ice shelf) (Antarctica = a lot, Greenland = a little).

Question 7

Characteristics of ice streams…

Answer 7

Ice streams are fast flowing ice bounded by slower moving ice.

Low driving stress therefore, ice deformation is not so significant.
But they are FAST, so SLIDING or subglacial DEFORMATION must occur.

They are underlain by water saturated till - it’s rheology is important.

Question 8

What is Antarctic Regional Mass Balance doing today.

Answer 8

Losses OUTPACED gains, with grounded-ice loss from Greenland (200 billion tonnes per year) and Antarctica (118 billion tonnes per year) contributing 14 millimetres to sea level (2019).

Question 9

On average, how much since 1992 have polar ice sheets contributed to the global sea-level rise?

Answer 9

0.59 +/-0.20mm/yr.

Since 1992, the polar ice sheets have contributed, on average, 0.59 +/-0.20mm/yr to the rate of global sea-level rise.

Question 10

Where on Antarctica is there a weak underbelly?

Answer 10

Thwaites Glacier and Pine Island glacier, Amundsen sea sector.

Question 11

What are the key processes of ice-shelf calving and stability?

Answer 11

1. Ice shelves displace their equivalent volume in seawater.
2. Ice shelves buttress the flow of inland ice.
3. Ice shelves interact directly with the ocean.
4. Ice shelves on the Antarctica Peninsula are changing.
5. Calving is influenced by summer temperatures.

Question 12

What is calving influenced by?

Answer 12

Summer temperatures.

Question 13

Do lakes exist beneath the Antarctic Ice sheet?

Answer 13

Yes, lakes exist beneath the Antarctic Ice Sheet. And some of these lakes are active.

They are maintained by basal meltwater, geothermal heat flux, and the pressure of the melting point.

Question 14

What maintains the lakes beneath the Antarctic Ice Sheet?

Answer 14

They are maintained by basal meltwater, geothermal heat flux, and the pressure of the melting point.

Changes in these are important for ice sheet dynamics.

Question 15

What is important for ice flow?

Answer 15

Subglacial water.

Question 16

What are some characteristics of Polar sea ice?

Answer 16

• They are frozen ocean water.
• Sea ice grows and decays SEASONALLY.
• Largest seasonal change on the planet.
• Hugely important for Earth’s energy budget.
• Decline in North Polar Sea Ice.
• Antarctic stable or increasing?

Question 17

What is the largest seasonal change on the planet?

Answer 17

Polar sea ice

changes seasonally

Question 18

What do we know?

Answer 18

• Recent observations show the ice sheets are sensitive to changes in their margins.
• Antarctica both influences and is influenced by the ocean.
• Antarctica is losing mass (are the recent changes significant or part of a natural cycle?)

Question 19

What don’t we know?

Answer 19

Are we aware of all the key processes and feedbacks in the system?
Is the Ross Ice Shelf and West Antarctica stable?
Is the East Antarctic stable?