Antarctica Evolution
Land of extremes
= land of erosion extremes
Evidence for both:
catastrophic erosion rates in places
very low erosion rates elsewhere
Why such low erosion?
Polar climate
Very cold temperatures for v long time (Ma)
Dry Valleys
Near transantarctic mountains
where precipitation levels = very low
Main EAIS ice discharged via a few conduits
Ice sheet evo studies
Process / satellite studies
Evolution studies
tell us what is happening now
Tell us what has happened
Importance: Provide
- Trajectory by which to judge signif of current msmts
- Historical record by which to test/calibrate models
- Evidence of most important processes
Antarctic Evolution
- Australia separated from Antarctica ~ 45 Ma
- Birth of Antarctica ~34 Ma
Antarctica isolated from S. America w Drake Passage opening
Antarctic Circumpolar Current isolates climatically
- Final separation ~30 Ma
Global ↓ pCO2
Himalaya uplift & erosion too ?
Before Rift (Preglacial)
Climate was warm
akin to NE Australia (tropical)
before final rift ~ 52 Ma
Fluvial landscape
Dendritic river networks beneath EAIS
River graded to sea
Inselbergs - isolated mountains
AIS Birth ~ 34 Ma
CO2 decline & opening Drake's Passage
Nucleation points
= high mountain areas
∴ small mountain ice caps
--> grew into cont regional ice sheets
AIS Climate
Up to Mid-Miocene (34-14 Ma)
After Mid-Miocene
(14 Ma - present)
Prolonged cold period
No fluctuation in climate
Climate oscillations
Where AIS nucleated?
High mountain areas
Gamburtsev mtns
Dronning Maud Land
Transantarctic mountains
Cape roberts offshore drilling (Naish, 2001)
Core revealed
33 glacial cycles 34 - 17 Ma
Overall cooling trend
No sediments after 17 Ma
Not cont scale IS
As lotsa veg survived
Scrub forest / moss tundra in favourable locations ~ 24.3 - 18 Ma
Lotsa meltwater sed deposits @ each deglacial
S. Beech pollen
Characteristic of S. Patagonian climate today (T=4-12°C)
∴ Alpine style glaciation @ Eocene-Oligocene boundary
Distinct climate ∆ ≈ 14 Ma
- Large cooling
upto 7°C Pacific
up to 8°C in McMurdo Range
- Transition from warm
--> cold-based glaciation
- Ice sheet reached outer cont margin
Max extent ≈ 14 Ma
Eroded major troughs
- Retreat back onto land ≈ 13.6 Ma
Sirius Till
Diamict - clay & gravel/boulders
Clay evinces warm-based deposit
Found throughout Transantarctic Mtns
Dated ~ 14 Ma
after which evidence for more cold-based ice seen
AIS expansion/ contraction
Driven primarily by sealevel ∆
Antarctica is SO dry
∴ climate has little effect
Since 13.6 Ma, polar conditions have prevailed