Late Paleozoic Ice Ages
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
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.