Chapter 10

1
Chapter 10 Insolation control of ice
sheets

• Ruitang Soong

2
Outline

• What controls the size of ice sheet?
• Modeling the behavior of ice sheets
• North hemisphere ice sheet history

3
What controls the sizeof ice sheet?

• Elevation Latitude
• Temperate
• Insolation
• Orbit of Solar-Earth

Figure 10-1
4
Orbital-scale control of ice sheetThe
Milankovitch theory

• Key point Summer insolation
  control of ice sheets
• Previous study
• J.A. Adhemar (1842)
• James Croll (1864, 1875)
• Milutin Milankovitch (1915 1940)

combined precession, eccentricity, and tilt.
Chose summer in the northern high latitudes as
the important season predicted warm periods at
125, 105, and 82 ka.
5
Diagram depicting variation in precession. Image
by Robert Simmon, NASA GSFC. Taken from
http//earthobservatory.nasa.gov/Library/Giants/Mi
lankovitch/milankovitch.html. 
6
Figure 10-2
Figure 10-3
7
Modeling the behavior of ice sheets

• weak insolation in summer
• Ice growth, ice bedrock depression
• strong insolation in summer
• Ice melting, ice slipping calving, bedrock
  swelling
• Two feedback mechanism

8
Insolation Control of ice sheet size

• Climate point
• Equilibrium line

Figure 10-5
9
Figure 10-7
Figure 10-6
10
Ice sheet lags behind summer insolation forcing

• Ice volume response to lnsolation

where l is ice volume
d(I)/d(t) is the rate of change of ice volume per unit of time (t)
T is the response time of the ice sheet
S is the curve of changing summer insolation
Figure 10-8
11
Figure 10-9
12
Delayed bedrock response beneath ice sheet

• Elastic response
• Viscous response

Tack from Richard E. Goodman, Introduction to
Rock Mechanics, 2/e, 1989,Wiley
Figure 10-10
13
Figure 10-11 Bedrock feedback to ice growth and
melting Insolation control of ice sheet size the
initial lag of ice volume behind insolation the
subsequent lag of bedrock depression and rebound
behind ice loading and unloading
14
Full cycle of ice growth and decay
Figure 10-12
15
Ice slipping and calving

• Basal slipping (terrain, stress)
• Calving
• Ice sheet models can be coupled to 3D GCM models.

16
North hemisphereice sheet history
17
Conceptual Model Evolution of ice sheet cycles

• Changes in summer insolation (shorter-term
  change)
• Gradual global cooling (longer-term change)
• Note
• cycle of tilt is 41,000 year
• cycle of precession is 23,000 year
• cycle of eccentricity is 100,000 and 413,000 year

Figure 10-13
18
Figure 10-14
19
Evidence from d18OHow ice sheets actually
evolved

• Ocean sediments contain two key indicator of past
  glaciations
• Ice-rafted debris
• d18O

N. Shackleton
Figure 10-15
20
Figure 10-16
Figure 10-17
21
Confirming ice volume changeCoral reefs and sea
level

• d18O (ice volume)
• Radiocarbon (234U?230Th)
• Ice-rafted debris
• Coral reefs (sea level)

22
Box 10-3
23
Using astronomical and d18O signals as a
chronometer

• Orbital tuning

Figure 10-21