Ensuring Technical Readiness For Copilot in Microsoft 365
Eocene Oligocene Transition Class Presentation By Kedar Ghimire
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
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.
7.
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.
9.
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.