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Did WAIS collapse during last interglacial? (Blue ice moraine formation…
Did WAIS collapse during last interglacial?
WAIS: dynamic or stable?
Uncertainty surrounds stability over past glacial cycles
Dynamic
thickened during glacials
collapsed during interglacials
Stable
Model fluctuations
Previous studies
Farfield records
corals record 6-9m higher global sealevel @ last interglacial
some posit WAIS collapsed since it holds ~6m SLR potential
Other evidence
suggests WAIS
declined
but did not collapse
Open seaway btwn N & S WAIS
Theory open seaway btwn Weddell & Ross Seas
Proposed since:
Marine microfossils
found beneath ice streams supplying Ross Ice Shelf
oldest core ~70kyr ∴ not long enough to study last ig
Octopi genetics
display marked similarity in Ross & Weddell Seas (unconnected today)
∴ evidence
suggesting
WAIS collapsed, but
no smoking gun
Controversy
evidence for minimal thickening
∴ dynamics suggest would also be minimal thinning
Blue ice moraine formation
Katabatic winds
descend lee side of topog (relatively consistent direction)
erode @ base of mountains
∴ Creates surface gradient
pointed toward mountains
Ice flow preferentially towards mountain
Result:
Compression @ foot of mountains
Brings deep ice to surface
∴ Basal material brought from bed to surface as debris bands
Regelation ice
sed etc from glacier bed makes ice dirty
Blue ice moraine
Debris upwelled from glacier bed
= draped throughout landscape
Areas high topog nr modern g.l.
evince ∆ ice surface elevation
Heritage Range
Area high topog nr modern g.l.
2 areas of drift
Lower slopes
Covered in boulders / erratics
Lotsa fresh material
Glacial ice preserved
Upper slopes
Debris accumulated in lee of obstacles
--> cold-based ice
Exposure ages
(assuming constant exp
Lower slopes = younger [< 50 ka]
Higher slopes = older [600 ka - 1 Ma]
Banana
Plot
Black line = line contunous exposure
High elevation samples
Exposed continuously according to Al-26/Be-10
Low elevation samples
Prolonged burial inferred
Interp exposure & burial history
Glacial times
Ice thickened to higher elevations
∴ blue ice moraine deposits left there
Over time
Ice surface lowered
but evidence for fluctuations
If whole WAIS deglaciated fully
expect:
Fjord situation
∴ marine diatoms - none found
Reglaciation w radial flow
i.e. high mtn/cirque glaciation
no evidence
Instead, evidence suggests:
stable conditions for ~1.4 ma
WAIS CONCLUSIONS
Atleast ice cap remained
∴ Central divide survived Pleistocene interglacials
∴ Max interglacial sealevel contrib ~3.3 m