Global cooling at the Eocene Global cooling at the Eocene – – Oligocene Oligocene transition transition­ ­ “ “the world turned cold the world turned cold” ”

Environmental Geosciences, class presentation Environmental Geosciences, class presentation IOR IOR­ ­ Prof. Dr. Andrea Prof. Dr. Andrea Koschinsky Koschinsky­ ­Fritsche Fritsche

Presented by Kedar Ghimire, Presented by Kedar Ghimire, May 8th, 2007 May 8th, 2007

Title Image: Moeritherium

Hello !, Sorry I am extinct

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

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 "dawn" of modern ('new') mammalian fauna, appeared during the epoch

Middle Eocene ,Scotese, C. R., 1997. Paleogeographic Atlas, PALEOMAP Progress Report 90­0497, Department of Geology, University of Texas at Arlington, Arlington, Texas, 37 pp

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

Oligocene epoch

http://www.utexas.edu/opa/news/03newsreleases/nr_200312/nr_anthropology031203.html

• 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

Eocene Eocene­ ­Oligocene Transition Oligocene Transition • • "greenhouse" climates of the Eocene were replaced by the "icehou "greenhouse" climates of the Eocene were replaced by the "icehouse" se" conditions that persist today. conditions that persist today.

• • Analysis of Sedimentary rocks. Major extinctions for gastropods, Analysis of Sedimentary rocks. Major extinctions for gastropods, amphibians and reptiles, little change to mammals amphibians and reptiles, little change to mammals

• • Causes Causes • • Dupont Dupont­ ­Nivet Nivet et al. and et al. and Zanazzi Zanazzi et al. implicate it to the declining et al. implicate it to the declining levels of atmospheric levels of atmospheric CO CO2 . 2 .

• • Ocean circulation hypothesis by Ocean circulation hypothesis by Shackleton Shackleton and Kennett . During and Kennett . During Paleocene, Australia and Antarctica were joined. In the early Eo Paleocene, Australia and Antarctica were joined. In the early Eocene cene (t=~55 (t=~55 m.y m.y. ago), Australia began to drift northward from Antarctica. . ago), Australia began to drift northward from Antarctica.

• • During the Eocene (t=55 to 38 During the Eocene (t=55 to 38 m.y m.y. ago) the Southern Ocean was . ago) the Southern Ocean was relatively warm and the continent largely relatively warm and the continent largely nonglaciated nonglaciated. By the late . By the late Eocene (t=~39 Eocene (t=~39 m.y m.y. ago) a shallow water connection had developed . ago) a shallow water connection had developed between the southern Indian and Pacific oceans and also probably 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.

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

Eocene Eocene­ ­Oligocene Transition Oligocene Transition • 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

Eocene Eocene­ ­Oligocene Transition Oligocene Transition • • Findings of Findings of Zanazzi Zanazzi et. al et. al • • Zanazzi Zanazzi et. al. methods lag the determined age of et. al. methods lag the determined age of eocene eocene­ ­oligocene oligocene transition time period by approx. 400 transition time period by approx. 400 Kyr Kyr compared to marine methods compared to marine methods

• • They made sure that all They made sure that all taxa taxa experimented were water experimented were water­ ­dependent. dependent. • • No resolvable change seen in mean enamel No resolvable change seen in mean enamel δ δ18 18O, suggests that water O, suggests that water composition remained unchanged. composition remained unchanged.

• • Statistical variance ( Statistical variance (var var) for Eocene vs. Oligocene teeth ) for Eocene vs. Oligocene teeth – – indistinguishable, suggests no major change in MART across the indistinguishable, suggests no major change in MART across the transition or a possibly small increase. transition or a possibly small increase.

• • Shows decrease in MAT of 8 Shows decrease in MAT of 8° °C, far larger than found in marine records C, far larger than found in marine records­ ­ 2 2­ ­3 3° °C C

• • MAT (Eocene)=21.0 MAT (Eocene)=21.0± ±10.1 10.1° °C; MAT (Oligocene)= 13.1 C; MAT (Oligocene)= 13.1± ±9.5 9.5° °C; C; δ δMAT(EOT)= MAT(EOT)= ­ ­8.2 8.2± ±3.1 3.1° °C C

• • Results say that decrease in MAT rather than an increase in seas Results say that decrease in MAT rather than an increase in seasonality onality 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.

Discussion and conclusion Discussion and conclusion

• • Asian drying and early Asian drying and early oligocene oligocene climate change climate change are linked. are linked.

• • One thing to be tested: whether the regional One thing to be tested: whether the regional tectonic events caused both the observed tectonic events caused both the observed aridification aridification and climatic change in Antarctica. and climatic change in Antarctica.

• • Himalayan uplift could have caused a rain Himalayan uplift could have caused a rain shadow , simultaneously triggering a global shadow , simultaneously triggering a global reduction of CO reduction of CO2. 2.

• • The The eocene eocene­ ­oligoscene oligoscene transition was a turning transition was a turning point for whole of earth and not only point for whole of earth and not only antarctica antarctica. .

Thank you for your kind attention! Thank you for your kind attention!

Reference: Reference: • • JP Kennett JP Kennett ­ ­ Journal of Geophysical Research, 1977 Journal of Geophysical Research, 1977 • • Zanazzi Zanazzi, A., Kohn, M. J., , A., Kohn, M. J., MacFadden MacFadden, B. J. & Terry, D. O. , B. J. & Terry, D. O. Jr Jr Nature Nature 445, 639 445, 639– –642 (2007) 642 (2007)

• • DeConto DeConto, R. M. & Pollard, D. Nature 421, 245 , R. M. & Pollard, D. Nature 421, 245– –249 (2003) 249 (2003) • • http://www.nature.com/nature/journal/v445/n7128/full/445607a.htm http://www.nature.com/nature/journal/v445/n7128/full/445607a.html l • • http://www.3dvalley.com/gallery/d/3275 http://www.3dvalley.com/gallery/d/3275­ ­2/moeritherium4.jpg 2/moeritherium4.jpg • • http:// http://en.wikipedia.org/wiki/Eocene en.wikipedia.org/wiki/Eocene • • http://www.mnh.si.edu/anthro/humanorigins/faq/gt/cenozoic/oligoc http://www.mnh.si.edu/anthro/humanorigins/faq/gt/cenozoic/oligoce e ne.htm ne.htm

• • http:// http://www.palaeos.com/Cenozoic/Oligocene/Oligocene.htm www.palaeos.com/Cenozoic/Oligocene/Oligocene.htm • • http://scotese.com/oligocen.htm http://scotese.com/oligocen.htm • • http://en.wikipedia.org/wiki/Wiki http://en.wikipedia.org/wiki/Wiki

• • Kedar Ghimire Kedar Ghimire