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Ellsworth Implications (Oxygen isotope curve (temp proxy) (Eocene -…
Ellsworth Implications
Ellsworth mtn trimline
Argued it could be older ? (mid-Miocene ~15 Ma)
What ?
Line on mtnside marks highest extent of glacier/ erosional activity
Date ?
Rock core min age = 3.5 - 5.1 Ma
Why older?
∴ Must've been warm-based ice to form striations
Coldest temp at which water exists @ base
Greenland = -11°C
Ellsworth last @ this temp during Mid-Miocene ?
Present MAT Ellsworth = 30°C
Rock striated
@ thin upper margin Ellsworth IS
Oxygen isotope curve
(temp proxy)
Eocene
-
cooling
~34 Ma
-
Sharp drop
temps
Oligocene/Miocene
- Stable, fluctuating
Mid-Miocene
- Step cooling
Ice Extents for Iso Stages
Jamieson (2010)
Eocene
Local valley glaciers only ?
Oligocene
(early Miocene)
Cycles of ∆ ?
Growth, then retreat etc
Mid-Miocene
Cooling
∴ Dispersed ice extent developed
Antarctica covered
Olympus Range
Marshal
Change from cold → warm regime evinced @ Olympus Range
Dated ~14 Ma
Why 14 Ma ?
Agrees w Jamieson IS model
Cooled Patagonian (2°C) climate in stepped increments
By Mid-Miocene temps ~ -12°C
Warm-based ice in Ellsworth both:
initially
during IS growth
Mid-Miocene probs last time
Temps sufficiently warm in Ellsworth
(-12°C)
∴ meltwater @ bed
(warm-based ice)
WAIS stability implications
Katabatics & ice sheet present in Ellsworth > 2.5 Ma
Modelled WAIS interglacial ice 200, 500 years ago & future
after Pollard & DeConto
doesn't include climate
in Heritage Range
Ellsworth shows
Katabatics producing blue ice moraines
in Ellsworth for 2.5 Ma (if not 5)
Fluctuating ice extent
older higher
younger lower
No deglaciation though
area consistently glaciated
Likely WAIS fate in a warmer world?
Two possible explanations cosmogenics
1. Entire WAIS survived warm periodsn
Regional upland ice sheets persisted
during warm periods
Cannot tell which scenario applies from Ellsworth data alone
Sugden Hypothesis
Mountain uplands
stable a long time
Probably local ice stream
May happen to WAIS in future
Lose marine IS part in middle
Left w/3 regional ice sheets on uplands
(assuming 2 m SLR atop expected)