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Chapter 10— Insolation control of ice sheets
Ruitang Soong
Outline
What controls the size of ice sheet? Modeling the behavior of ice sheets North hemisphere ice sheet history
What controls the sizeof ice sheet? Elevation & Latitude Temperate Insolation Orbit of Solar-Earth
Figure 10-1
Orbital-scale control of ice sheet:The Milankovitch theory Key point Summ
er 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.
Diagram depicting variation in precession. Image by Robert Simmon, NASA GSFC.Taken from http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/milankovitch.html.
Figure 10-3
Figure 10-2
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
Insolation Control of ice sheet size
Climate point Equilibrium line
Figure 10-5
Figure 10-6
Figure 10-7
Ice sheet lags behind summer insolation forcing
Ice volume response to lnsolation
)(1
)(
)(lS
Ttd
ld
where l is ice volumed(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
Figure 10-9
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
Figure 10-11 Bedrock feedback to ice growth and meltingInsolation 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
Full cycle of ice growth and decay
Figure 10-12
Ice slipping and calving
Basal slipping (terrain, stress) Calving Ice sheet models can be coupled to 3D GCM
models.
North hemisphereice sheet history
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
Figure 10-14
Evidence from δ18O:How ice sheets actually evolved
Ocean sediments contain two key indicator of past glaciations
Ice-rafted debris
δ18O
N. ShackletonFigure 10-15
Figure 10-16Figure 10-17
Confirming ice volume change:Coral reefs and sea level δ18O (ice volume) Radiocarbon (234U→230Th) Ice-rafted debris Coral reefs (sea level)
Box 10-3
Using astronomical and δ18O signals as a chronometer Orbital tuning
Figure 10-21