Retreating Ice Shelves

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Retreating Ice Shelves

• By Chris Wagner

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What Are Ice Shelves??

• An Ice Shelf is a fixed, floating glacier which
  extends out from shore over a large area of the
  sea
• Only form in polar regions where ice is below
  pressure melting point

(Benn Evens, 1998)
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Ice Shelf Classification

• Glacier Ice Shelves
• Sea-ice Ice Shelves
• Composite Ice Shelves

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Glacier Ice Shelves

• Formed when a glacier terminates into the sea and
  is forced to float
• Many examples around Antarctica
• Milne Ice Shelf, Canadian Arctic
• Account for most of ablation on glaciers that
  terminate into the sea

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Sea-Ice Ice Shelves

• Created by a combination of surface snow
  accumulation and bottom freezing of sea-water
• Movement and deformation is self induced
• Only occur where temperatures are cold enough for
  the sea to freeze over and close enough to anchor
  on something so it is not disturbed by waves or
  currents
• Surface rolls are characteristic of high Arctic
  Sea-Ice ice shelves
• Characteristic isotopic and crystallographic
  signatures

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Composite Ice Shelves

• Formed by combining floating glaciers and
  thickening sea-ice
• Cape Alfred Ernest on Ellesmere Island is a good
  example
• Many in Antarctica, but their origins are well
  disquised

(Benn Evens, 1998)
Cape Alfred Ernest
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Antarctica Ice Shelves

• Major shelves are the Ronne-Filchner and Ross,
  which are fed by East and West Antarctica Ice
  Sheets
• Drain 62 of Antarctica
• Move between 0.9 And 2.6 km/yr and make up for
  large scale calving
• Extensive cliff margins along shelf edges

Ross Ice Shelf, Antarctica

• 7 of surface area is made up by ice sheets
• 44 of the coastline
• 80 of the ablation

Great Barrier, Antarctica
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Ice Shelf Flow

• Caused entirely by creep spreading from weight of
  ice above water line, as there is no basal stress
• Thinning out towards margins occurs, but can be
  counteracted by surface accumulation and basal
  freezing

(Benn Evens, 1998)
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Stability

• Calving is important in regards to stability
• Mass balance is also dependant on accumulation
  and ablation on the shelf surface, as well as
  melting and freezing below surface
• Net ablation and basal melting results in shelf
  disintegration
• Protected area with no waves or currents are best
• Extensive flow from source glacier is beneficial

(Benn Evens, 1998)
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Larsen Ice Shelf Instability

• Larsen B Ice Shelf had 3250 km2 break off in 2002
• Released over 700 billion tonnes of ice
• Largest iceberg to break off was B-15 with an
  area of 11000 km2

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Shelf Instability

• Progressively thinning and becoming affected
  easier by currents and waves
• Temperature increases are aiding in the ablation
  of ice shelves
• Increase in water temperature also aiding with
  melting from below, this could be due to changing
  currents
• No longterm weather information, so there are
  many questions that are unanswered!

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Problems Due to Shelf Disintegration

• Icebergs are more common
• Create treacherous shipping routes and problems
  with oilfields and buried lines when icebergs
  come into contact with the infrastructure
• Increase in sea level, may affect the cities
  located so close to oceans
• May influence the worldwide climate

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References

• Post, A. and LaChapelle E.R. 2000. Glacier Ice
• Menzies, J. 1995. Modern Glacial Environments
  Processes, Dynamics and Sediments

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Questions???