Glacier Response Times

1
Glacier Response Times

• All glaciers are, by definition, permanent.
• Each respond to climate across characteristic
  timescales.
  
• Ice sheets X000 years
• Ice caps X00 years
• Glaciers X0 years
• Glacierets X years

2
Glaciers as Systems

• Best viewed as an open system
• Mass and energy in
• Radiation, rockfall snow
• Movement and work
• Erosion, transport, deposition
• Mass and energy out
• Long-wave radiation till, meltwater

INPUTS
OUTPUTS
Atmosphere
Atmosphere
Lithosphere
Lithosphere
Hydrosphere
Hydrosphere
3
The Global Cryosphere
Sugden John, 1976

• Ice Sheets and their behavior
• Theory
• Antarctica
• Laurentide
• Fennoscandian/Barents
• Dominantly from Hughes, T. J. (1998) Ice Sheets

4
Theory first approximation

• Ice Sheets are defined as subcontinental or
  larger ice masses that define their own
  topography.

5
Schematic second approximation
6
Theory Ice Sheet Flow

• As the ice deforms, it moves away from its
  initial point both downward and outward

7
Schematic Ice Sheet Flow
Pure shear
combinations
Simple shear
complexities
8
Ice Sheet Stability

• Ice sheets, unlike glaciers, commonly display
  instability associated with positive feedback
  loops

9
(negative feedback)
As ice sheet shrinks, ablation area decreases
(positive feedback)
As ice sheet shrinks, accumulation area decreases
10
Antarctic Ice Sheet

• 12.5 x 106 km2
• Partly terrestrial-based
• East Antarctic
• Partly marine-based
• West Antarctic Ice Sheet (WAIS)

11
Larsen I.S.
W.A.I.Sheet
12
Ice Shelves

• Floating
• Thin (X00 m)
• Variable budget

• Major loss calving
• Unstable!
• Pinning points

13
Topographic Profile

• Surface slopes
• Bed elevations
• Ice shelves

14
Ice Flowlines

• Ice sheet flow is more complex than one might
  think!

15
Nunataks

• McMurdo Dry Valleys
• Nunataks (unglaciated terrain surrounded by ice)
  are surprisingly significant
  
• Ice reconstruction
• Biological refugia
• Ecological curiosities

Courtesy NASA Earth Observatory
16
Ice Streams

• Focused flow within an ice sheet
• Velocity x 100
• Drains ice domes
• Carves bed

17
Ice sheet initiation

• Theories
• Highland/windward
• Mountains first
• Instantaneous glacierization
• Lowlands first
• Marine ice transgression
• Oceans first

18
Past ice sheets

• Alternative hypotheses
• Arrows wind/H2O
• Black nucleation
• How can they be tested?

19
Laurentide

• Sugden (1977)
• Simple profile model
• Single central dome
• Equilibrium ice sheet

20
Laurentide

• Clark (1996)
• Inferred from uplift
• Several domes
• Dynamic ice sheet
• Truth?
• This plus time variation

21
Fennoscandian/Barents

• Sensitive to sea level
• Early initiation?
• Late growth?
• Early decay?

22
Laurentide decay

• Radiocarbon dated
• Variable rates
• ?area ?volume ?sea level
• Laurentide drives Barents?