Elevation Feedback & Binge-Purge (Laurentide IS Binge-Purge (Result:…
Elevation Feedback & Binge-Purge
May have cooled climate?
freshwater flux into N.Atantic interrupted overturning circulation?
Explain Heinrich events (2 pulses IRD on Atlantic seafloor)
Possibly binge purge oscillations ?
2.Late purge IRD output
Freeze-on of basal debris
--> indicates return to frozen bed ?
Mid purge IRD hiatus
when initial debris melted off
1. Initial IRD output (first ice bergs released)
= armada of debris laden ice bergs
Two peaks ice rafted debris
Limited Evidence IS Drawdown
= only plausible mechanism for these deposits to reach seafloor
∴ Releasing debris they entrained on IS
Bergs melt out at sea in Atlantic
Ice bergs calve from Hudson Bay
Lithic fragments of continental origin on Atlantic seafloor
Only evidence binge purge = Ice rafted debris
Laurentide IS Binge-Purge
Result: Fast drawdown of ice sheet
--> Insulation stops ∴ bed refreezes --> Ice sheet builds up again
3. Ice thins to maintain mass continuity
following mass loss to ocean
2. Meltwater lubricates bed
∴ ice flows into ocean @ Hudson Bay
1. Thickening Laurentide IS insulates bed
causing relative warming allowing melt
If from Antarctica, could it happen again?
Debated whether caused by melt from Laurentide or Antarctica
When ? ~ 14 kyr
16-25 m sea level rise in ~ 500 years
Rapid Collapse Laurentide IS
Cause of Meltwater Pulse 1a?
∴ Portion of Laurentide decayed
from 2 km thick to nothing in ~500 years
Altitude-melt feedback ∴ runaway melt
Slight depression developed just E of Rockies
∴ lowered ice surface elevation
Possible Causes 100 kyr Cyclicity
2. Elevation feedback & binge-purge
Clarke & Pollard Regolith Mechanism
∴ Runaway effect:
Thinned ice sheet --> greater surface melt --> faster thinning
Elevation dependence of temp
--> means ice sheet surface warms as it thins
Modelled rapid collapse Laurentide IS
--> using altitude-melt feedback
Temp - Altitude Dependence
Mountains: with increasing altitude-temps decrease ∴ more snow
= Possible cause rapid ice sheet decay ?
Ice: Small lowering of ice surface due to instability
--> Runaway melt
Ice Sheet Termination
Albedo loss from ice melt --> accelerates warming rate
Jagged sawtooth pattern
= sharp transition from glacial to interglacial
What makes ice sheets disappear rapidly ?