Late Paleozoic Ice Ages

Gabe Joseph

EOS 191

The Paleozoic

Biologically complex Earth
Landmass in south
Low CO2 (around current levels)

Ice Ages

Ice ages lasted ~72m years

Mississippian to Late Permian

Ice Extent

Traditional: one large ice sheet
But the mass-balance doesn't add up!
Instead: small, brief ice centers (1-8myr)
Didn't wax and wane in sync

Evidence

&

Mechanisms

Cyclothems

Mechanism 1:

CO2 Drop

Decrease in CO2 ~350mya
Coincides with first trees
Trees remove CO2:

Accelerate silicate weathering
Bury carbon upon death

Plants had largest effect on CO2
Model agrees with paleosols, stomata

CO2's Role

CO2 controls mean climate (icehouse or hothouse)

CO2 can't explain each glaciation: changes are too rapid

Mechanism 2:

Orbital Forcings

Orbital eccentricity matches cyclothems

Eccentricity

(variation of orbit between ellipse and perfect circle)

Circular: each season pretty much same year-to-year

Elliptical: stronger seasonality

Eccentricity controls climate variability

Gray: low eccentricity → low variation
White: high eccentricity → high variation
Constant mean (from CO2)

Eccentricity and Cyclothems

Orbit affects not just glaciers, but rainfall at low latitudes
i.e., latitudes where cyclothems form
Cyclothems show local runoff + glacial eustacy?

Orbit put the 'cyclo' in cyclothem
CO2 set mean climate where transition in and out of glacial was possible

Eccentricity usually minor, which constrains other forcings to not outweigh it

CO2 between 420-840ppm for eccentricity to cause cyclothems

Why: CO2

When: Eccentricity

Where: Orogeny

Mechanism 3:

Orogeny

Uplift of proto-Andes initiated glaciation
Alpine east Australia retained glaciers after poles

Equilibrium Line Altitude

Influenced by energy input, precipitation, topography, latitude, etc.
Hard to paleo-estimate
Not just climate: glaciers won't form without land in right place to form upon

Paleozoic Parallel

End of Paleozoic as an analogy for today:

Similar CO2 levels
Leaving an ice age (in geologic time)
Similar(ish) tectonic configuration

Bibliography

Daniel E. Horton, Christopher J. Poulsen, Isabel P. Montañez, William A. DiMichele. Eccentricity-paced late Paleozoic climate change. Palaeogeography, Palaeoclimatology, Palaeoecology, Volumes 331–332. 1 May 2012. Pages 150-161. ISSN 0031-0182, http://dx.doi.org/10.1016/j.palaeo.2012.03.014.

John L. Isbell, Lindsey C. Henry, Erik L. Gulbranson, Carlos O. Limarino, Margaret L. Fraiser, Zelenda J. Koch, Patricia L. Ciccioli, Ashley A. Dineen. Glacial paradoxes during the late Paleozoic ice age: Evaluating the equilibrium line altitude as a control on glaciation. Gondwana Research, Volume 22, Issue 1, July 2012, Pages 1-19, ISSN 1342-937X, http://dx.doi.org/10.1016/j.gr.2011.11.005.

Berner, Robert A. The Rise of Trees and How They Changed Paleozoic Atmospheric CO2, Climate, and Geology. Ecological Studies Volume 177, 2005, pp 1-7. 2005.

Saltzman, Matthew R. Late Paleozoic ice age: Oceanic gateway or pCO2? Geological Society of America, Volume 31. Sept 2002. Issue 2, Pages 151-154.

Oscar R. López-Gamundí, Luis A. Buatois. Introduction: Late Paleozoic glacial events and postglacial transgressions in Gondwana. GSA Special Papers 2010, v. 468, p. v-viii.