Global cooling occurred at the Eocene-Oligocene transition around 34 million years ago, when the warm "greenhouse" climate of the Eocene was replaced by cooler "icehouse" conditions with glaciers forming in Antarctica. Analysis of sedimentary rocks indicates major extinctions in gastropods, amphibians, and reptiles, with little change in mammals. Decreased atmospheric CO2 levels and changes in ocean circulation patterns are implicated as potential causes, with the development of the Antarctic Circumpolar Current helping to sustain Antarctic glaciation. Tooth enamel isotope analysis of mammal fossils provides evidence of an 8°C decrease in mean annual temperature at this transition.

1. Global cooling at the Eocene – Oligocene
transition­ “the world turned cold”
transition “
the world turned cold
Hello !,
Sorry I am extinct
Environmental Geosciences, class presentation
IOR­ Prof. Dr. Andrea Koschinsky­Fritsche
IOR Koschinsky
­
Presented by Kedar Ghimire,
May 8th, 2007
Title Image: Moeritherium

2. Source: http://www.williamsclass.com/images/GifImages/GeologicTime205K.gif

3. Eocene epoch
• Timeline­ (55.8 ± 0.2 ­ 33.9 ± 0.1 Ma) when earth
was free of large continental ice sheets
• In Greek, ἠώς (eos, dawn) and καινός (kainos, new).
­refers to the quot;dawnquot; of modern ('new') mammalian fauna, appeared during the epoch
CLIMATE
•Extreme global warming termed Paleocene­Eocene Thermal
Maximum or Initial Eocene Thermal Maximum (PETM or IETM)
•Deep ocean currents­ extremely warm. Temperate forests
extend to the poles Most homogeneous global climate.
•Grand Coupure­ the end of Eocene, causes could be due to
climate change with polar glaciations, bolide impact
Middle Eocene ,Scotese, C. R., 1997. Paleogeographic Atlas, PALEOMAP Progress Report 90­0497, Department of Geology, University of Texas at Arlington, Arlington, Texas,
37 pp

4. Oligocene epoch
• 34 million to 23 million years ago
• comes from the Greek ὀλίγος (oligos, few)& καινός (kainos, new)
• the sparsity of additional modern mammalian faunas after
a burst of evolution during the Eocene
• increase of volcanic activity and the plate tectonic movement
• The start of general cooling, glaciers forming in Antarctica for
first time, fall in sea level, tropics diminished, ice covered the
south pole but not north pole
• Cooling trend continued, culminated into ice age of Pleistocene
finally.
• followed by Miocene, then Pliocene, pleistocene and then
Holocene
http://www.utexas.edu/opa/news/03newsreleases/nr_200312/nr_anthropology031203.html

6. Eocene­Oligocene Transition
Eocene
­
• quot;greenhousequot; climates of the Eocene were replaced by the quot;icehousequot;
quot;greenhousequot; climates of the Eocene were replaced by the quot;icehou
conditions that persist today.
• Analysis of Sedimentary rocks. Major extinctions for gastropods,
amphibians and reptiles, little change to mammals
• Causes
• Dupont­Nivet et al. and Zanazzi et al. implicate it to the declining
Dupont
­
levels of atmospheric CO2 .
CO
• Ocean circulation hypothesis by Shackleton and Kennett . During
Paleocene, Australia and Antarctica were joined. In the early Eocene
Paleocene, Australia and Antarctica were joined. In the early Eo
(t=~55 m.y. ago), Australia began to drift northward from Antarctica.
m.y
• During the Eocene (t=55 to 38 m.y. ago) the Southern Ocean was
m.y
relatively warm and the continent largely nonglaciated. By the late
nonglaciated
Eocene (t=~39 m.y. ago) a shallow water connection had developed
m.y
between the southern Indian and Pacific oceans and also probably
the Drake passage. Substantial Antarctic sea ice began to form.
the Drake passage. Substantial Antarctic sea ice began to form.

8. Eocene­Oligocene Transition
Eocene
­
• Antarctic glaciation sustained by “Antarctic
“
circumpolar current”.
circumpolar current ”
• Thermohaline oceanic circulation was
initiated. (the global density­driven
initiated. (the global density
­
circulation of the oceans).
• HOWEVER, computer models suggest
something else.
something else.

10. Eocene­Oligocene Transition
Eocene
­
• Dupont­Nivet et al.(2007) applied precision dating
techniques to demonstrate that climatic change in central
asia occurred at the same time as the early oligocene
glaciation of antarctica.
• Zanazzi et al. (2007), using 18O/16O measurements in
tooth enamel from mammal fossils have provided
evidence of decrease in AAT of 8°C
• They measured relative abundance of oxygen isotopes in
ancient minerals. Depends upon the 18O/16O of water
from which mineral is derived and the temperature at the
time of formation.
• used 18O/16O measurements of tooth enamel from
mammal fossils­ estimated 18O/16O of body water. No
temperature dependence to these isotope compositions

11. Eocene­Oligocene Transition
Eocene
­
• Findings of Zanazzi et. al
• Zanazzi et. al. methods lag the determined age of eocene­oligocene
eocene
­
transition time period by approx. 400 Kyr compared to marine methods
• They made sure that all taxa experimented were water­dependent.
experimented were water ­
• No resolvable change seen in mean enamel δ18O, suggests that water
δ
18
composition remained unchanged.
• Statistical variance (var) for Eocene vs. Oligocene teeth –
Statistical variance ( var
indistinguishable, suggests no major change in MART across the
transition or a possibly small increase.
• Shows decrease in MAT of 8°C, far larger than found in marine records­
Shows decrease in MAT of 8 C, far larger than found in marine records
°
2­3°C
2 3
­ °
• MAT (Eocene)=21.0±10.1°C; MAT (Oligocene)= 13.1±9.5°C;
MAT (Eocene)=21.0 10.1 C; MAT (Oligocene)= 13.1 9.5
± ° ± °
δMAT(EOT)= ­8.2±3.1°C
δ ­ ± °
8.2 3.1
• Results say that decrease in MAT rather than an increase in seasonality
Results say that decrease in MAT rather than an increase in seas
or aridity is the primary cause of the extinctions of gastropods,
or aridity is the primary cause of the extinctions of gastropods
amphibians and reptiles associated with the EOT.
amphibians and reptiles associated with the EOT.

12. Discussion and conclusion
• Asian drying and early oligocene climate change
are linked.
• One thing to be tested: whether the regional
tectonic events caused both the observed
aridification and climatic change in Antarctica.
• Himalayan uplift could have caused a rain
shadow , simultaneously triggering a global
reduction of CO2.
reduction of CO
• The eocene­oligoscene transition was a turning
eocene ­
point for whole of earth and not only antarctica.
antarctica .

13. Thank you for your kind attention!
Reference:
• JP Kennett ­ Journal of Geophysical Research, 1977
• Zanazzi, A., Kohn, M. J., MacFadden, B. J. & Terry, D. O. Jr Nature
Zanazzi MacFadden
445, 639–642 (2007)
445, 639 –
• DeConto, R. M. & Pollard, D. Nature 421, 245–249 (2003)
DeConto , R. M. & Pollard, D. Nature 421, 245
–
• http://www.nature.com/nature/journal/v445/n7128/full/445607a.html
http://www.nature.com/nature/journal/v445/n7128/full/445607a.htm
• http://www.3dvalley.com/gallery/d/3275­2/moeritherium4.jpg
http://www.3dvalley.com/gallery/d/3275 ­
• http://en.wikipedia.org/wiki/Eocene
http://
• http://www.mnh.si.edu/anthro/humanorigins/faq/gt/cenozoic/oligoce
http://www.mnh.si.edu/anthro/humanorigins/faq/gt/cenozoic/oligoc
ne.htm
• http://www.palaeos.com/Cenozoic/Oligocene/Oligocene.htm
http://
• http://scotese.com/oligocen.htm
• http://en.wikipedia.org/wiki/Wiki
• Kedar Ghimire
Kedar Ghimire