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Ch. 7 - Cenozoic cooling: Greenhouse-to-Icehouse Transition

Evidence for global cooling, ocean circ. Δ, ice-sheet growth

colder, more ice warmer, less ice Cramer et al., 2009

Mechanisms: - Continental configurations - Gateways & ocean circulation - Weathering, CO2 decrease

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>6°C cooling

>7°C cooling

Lear et al., 2001

Miller et al., 1987

δ18O: T + ice volume Mg/Ca: T (complicated by [CO3-2], [Mg], species variability)

Combine both proxies global ice volume

δ18Ocalcite = δ18Oseawater * 0.23(T)

Cenozoic cooling: Tectonic-Scale Mechanism?

•  Polar position •  Lower volcanic CO2 emissions •  Increased chem weathering •  Tectonic changes

–  Paleogeography –  Key oceanic gateways open & closed –  Changes in ocean heat transport

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Cooling Earth & AA glaciation

Polar position hypothesis?

Tectonic-scale CO2 outgassing?

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Tectonic-scale CO2 outgassing?

Lear et al., 2001

Uplift-Weathering Hypothesis & CO2 drawdown?

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Cenozoic: India-Asia Collision Tibetan Plateau

  Initial collision ~50 Ma; major uplift since 40 Ma   Uplift continues today

•  Large region elevated

•  Not common - no large continental collisions 100-65 Ma

Mt. Everest

Tibetan Plateau

Colorado Plateau

Plateaus alter climate

-  Δ Jet Stream -  Alter evap/ppt, T patterns

- Weathering/CO2

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Tibetan-Himalayan complex - very large, high elevation

Monsoon system developed: steep slopes, heavy rainfall

high suspended sed & dissolved chem loads

increase global chem weathering (CaSiO3 + CO2 CaCO3 + SiO2)

Increase Chem Weathering Rates

Chemical Weathering proxy: hydrothermal + riverine Sr 87Sr/86Sr in marine carbonates 87Sr/86Sr increase since 40 Ma: Increase in uplift & chem weathering more Sr & higher value 87Sr/86Sr to ocean

No unique cause for 87Sr/86Sr changes - but chem weathering may have increased since 40 Ma, drawing down atm CO2

- BUT source rock may change (no change in chem weathering rate)

- Decrease in hydrothermal input

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Cramer et al., 2009

Evidence for global cooling, Ocean circulation change

Appearances

Ext

inctio

ns

10

20

30

40

Miller, Katz & Berggren, 1992

Aubry & Bord, 2009

Faunal & floral changes ocean & nutrient reorganization

Thomas & Gooday, 1996

Phytodetritus b.f.

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Widespread Eocene/Oligocene hiatuses (unconformities)

Eocene Oligocene

Eocene Oligocene

Broecker 1971 Colder, denser dw faster deep-ocean circulation rates Less time for CO2 to accumulate from biological pump Less corrosive to CaCO3

earliest Oligocene deepening of the CCD (33.7 Ma)

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First IRD around Antarctica

δ18O of mammal teeth & bone ~8°C E-O cooling (central North America)

Zanazzi et al. 2007

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Leaf margins

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Antarctic Glaciation

•  Ocean heat transport - opening of Tasman Gateway & Drake Passage formation of ACC thermal isolation Antarctic glaciation (Kennett et al. 1971)

•  Cenozoic atm CO2 declined below a threshold cooling & glaciation (Deconto and Pollard, 2003).

These are not mutually exclusive hypotheses!

2 mechanisms may have caused rapid climate change:

The CO2 Threshold Hypothesis (deConto and Pollard, 2003) Gateways not critical. Instead:   Gradual CO2 decrease & ice increase Threshold   Positive feedback (less weathering, high albedo) rapid ice buildup   ACC lowers pCO2 threshold for ice sheet growth (= occurs sooner), but is not a requirement

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Tectonic gateways affect ocean heat transport

Explore Antarctica - L. Crossley

Opening of Tasman Seaway

Opening of Drake Passage

Closing of Isthmus of Panama

  Two critical gateway changes:   E-O: open Drake Psg & Tasman Seaway ACC   10-4 Ma: Uplift of Isthmus of Panama stopped equatorial flow btwn Atlantic & Pacific

  Opening/closing of critical gateways changes:  heat & salt balance  ocean circulation

Antarctic Circumpolar Current - ACC   Largest ocean current (125 Sv; 106 m3/sec)   clockwise around AA, ~45°- 65° S

  Surface to 2000 - 4000 m deep   Thermal divide - intensifies meridional

overturning circulation “Mixmaster”   Impacts climate

AC

C Atlantic - WOCE data (http://ewoce.org) plotted w/ODV (http://odv.awi.de)

Drake Psg

Tasman Gateway

http://oceancurrents.rsmas.miami.edu/

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closed gateways

open gateways

Open gateways ACC development thermal isolation of AA continental glaciation

Poore et al. 1984; Miller et al. 1985, 1987, 1989; Wright et al. 1991,1992; Zachos et al. 1992, 1994, 1996; Diester-Haass 1996; Bohaty et al. 2003; Sexton et al. 2006; Katz et al. 2011, Borrelli et al.2011; Rabideaux et al.2011; Lear et al.2004; Coxall et al. 2005; Wade et al. 2004; Palike et al.2006; Tripati et al. 2006

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Katz et al. 2011

Ruddiman 2007, after Charles, Wright, & Fairbanks 1993

low δ13C AAIW

ASP-5 δ13C offset low O2, low δ13C intermediate water signal, “proto-AAIW” (Katz et al. 2011)

Cramer et al., 2009

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ACC Development

Thermal isolation

Increased wind

Cooling

Ice sheet expansion

Upwelling

Biological Productivity

Abundant and diverse biota

Increased equator-to-pole thermal gradient

Neogene increase in diatom abundance & diversity

Major contributor to biological pump

Deepening of Drake Psg 20-25 Ma

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Productivity Feedback Loop

Increased biological productivity (marine)

Deposition of organic carbon in marine sediments

CO2 drawdown in atmosphere

Cooling

Increased winds

Upwelling

The Monterey Formation - middle to late Miocene (12-17 Ma) - central coastal California - organic-rich, highly siliceous (diatomite) - often laminated (dysoxic) - petroleum source & reservoir

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Monterey equivalent sediments span the Pacific rim; Intensified upwelling & org C burial

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Cramer et al., 2009

Gateway, heat transport, & NHG - Isthmus of Panama Closure began ~10 Ma, complete by ~4 Ma

Redirected warm salty water into Gulf Stream less sea ice fm more open water more evaporation more snow NH ice sheet growth Major NHG 2.7 Ma

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The Great American Interchange: Closing of Isthmus of Panama mammal migrations

Monterey

EOT gateways, CO2

Panama

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~15 Ma = modern

Antarctic Ice Sheet

~70 Ma, largest Cretaceous, 40 m

~33 Ma, e. Oligocene, 55-80 m

~92 & 96 Ma, big Cretaceous, 25 m

~93 Ma, typical Cretaceous, 15 m

Maps from models Deconto & Pollard (2002) Sea-level from Kominz et al. (2008) update

Cenozoic cooling: Greenhouse-to-Icehouse Transition

Geological & geochemical records long-term & rapid pulses: - cooling - continental ice sheet growth

Why? Some combo of:

1) CO2 decrease - SFS, uplift & chemical weathering, biological pump [long-term (Cenozoic), threshold (E/O), event (Monterey)]

2) Gateways+ocean heat transport (ACC at E/O, Panama & NHG)

3) Continental configurations - polar & high-latitude locations were a prerequisite for glaciation, but not sufficient by itself.