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Regolith Mechanism (Regolith Role (∴ Later ice sheets = thicker (-->…
Regolith Mechanism
Regolith
Role
Regolith cleared away by earlier faster flowing ice sheets
∴ Later ice sheets = thicker
--> since bed is stronger without sediment cover
Thicker ice - more difficult to melt -->
cycle skipping
∴ 100 kyr cyclicity as some obliquity cycles missed
text
Cowley & Hyde Model
Global ice sheet model forced by:
Orbital cycles
CO2 level change
Replicated emergence 100 kyr cyclicity
Cause:
Long term global cooling due to CO2 drawdown
Facilitated by persistence of thicker ice sheets
Earth moving toward Snowball Earth ?
CO2 drawdown over past 3 Myr
Clarke & Pollard Regolith Mechanism
Earlier ice sheets
(before 1 Myr)
Thinner - regolith covered bed
Weaker bed ∴ faster sliding
Paced by obliquity (40 kyr)
--> Fast IS cleared away regolith
Regolith
= sediment from bedrock weathering
Evinces further S extent of earlier ice sheets (40 kyr cyclicity) in N. Am than later ones (100 kyr cyclicity)
Regolith
covering N.Am
Present before NH glacial cycles established
No longer present
Later ice sheets
(after 1 Myr)
Thicker - flowed slower on strong bed
∴ Caused cycle skipping
- 100 kyr cyclicity
Thicker ice sheet = more resilient to warming
Regolith
& Ice Flow
Sediment facilitates faster sliding in presence of water
Sediment weakens the bed ∴ larger Csliding
Ice ∴ thinner & flatter
--> since ice mass input no different
Same climate different lithology
Weak bed - further ice extent
reached in shorter time
∴ Thinner ice sheet
= more susceptible to melt
when climate warms
Less volume & warmer surface
Maintenance of Laurentide IS
Laurentide persisted longer after regolith removed
--> Cooled globe via albedo feedback etc
∴ Skipped obliquity cycles, hence 100 kyr cyclicity
Clark & Pollard Model 1998
Inferring cause = regolith
Forced climate with orbital cycle
Could replicate mid-pliocene transition
from 40 to 100 kyr periodicity
Possible Causes 100 kyr Cyclicity
1. Clarke & Pollard Regolith Mechanism
Elevation feedback & binge-purge