1. Implications of Mollusk Study
If results from Mississippi Embayment are representative of open ocean
SST in general and winter SST in particular higher at low latitudes in Eocene
Results are consistent with prediction of GCM models with high atmospheric CO2
Decrease in atmospheric CO2 and more significant winter cooling
Consistent with oxygen isotopic record from mollusks

2. Foraminifer Preservation
Diagenesis in foraminifera difficult to detect
Aggregates of morphologically discontinuous calcite microgranules that are fused together create smooth surface
Often display fine features (pores, spines, etc.)
Substantial porosity
A-F show well-preserved shell textures
G-I show poorly preserved shell textures

3. Textural Preservation in Shells
Pearson et al. (2001) high-resolution SEM observations of Paleogene and Cretaceous calcareous oozes
Revealed diagenetic recrystallation on micrometer scale
Yet pores, internal wall layering and surface ornamentation preserved
Pelagic calcareous oozes and chalks commonly used for paleoceanographic studies
Certain localities (impermeable clays) have texturally well-preserved shells

4. Isotopic Differences Preserved
Clay samples from continental shelf
Possible fresh water influence
Diverse fauna display normal depth habitat-isotopic relationships
Vertical red line indicates maximum inferred SST
d18O is considerably more negative (warmer SST)

5. Comparison of Clay and Ooze
Depth relationships retained; d18O different
Convergence of lines towards diagenetic calcite value
Suggests shells at Site 523 are 50% original, 50% diagenetic carbonate
Paleotemperature at 523 is 15°C lower than at RAS 99-17
Site 523 and RAS are same age. Lines connect species common to both sites. Diagenetic calcite from Site 523.

6. Conclusions of Foraminifera Data
Eocene-Cretaceous planktonic foraminifera isotope data from oozes and chalks “suspect”
Measured paleotemperatures from oozes and chalks too low
Isotopic differentials are reduced
Meridonal temperature gradients reduced
Bottom water temperatures constant
Low latitude surface temperature higher
Diagenetic shifts of tropical fauna more severe

7. Equator-to-Pole Gradient Steeper
Gradients constructed with clay data steeper
Low latitude SST warmer
Consistent with models including elevated atmospheric CO2
Pearson et al. (2001) suggest that “allows us to dispose of the 'cool tropic paradox' that has bedeviled the study of past warm climates”
Late Cretaceous
Middle Eocene
Late Eocene

8. Implications of the Results
If results are representative of open ocean
i.e., little affect from freshwater runoff
Strengthen the link between high levels of atmospheric CO2 and global warmth
Predicted considerable warming at all latitudes appears now consistent with paleo-SST data
Considerably more data are required to define equator-to-pole temperature gradient
Requires drilling of continental margin sites
Avoided in past due to hydrocarbon potential
New era of Ocean Drilling removes restriction

9. Climate Change During Last 55 my
Global cooling over last 55 my
Terrestrial records
Faunal change
Floral changes
Evidence for glaciations
Marine records
Oxygen isotopic composition of foraminifera

10. Temperature from Leaf Margins
Leaves in warm climates have smooth margins
Leaves in cold climates have irregular edges

11. Paleotemperaures from Leaves
Analysis of leaf edge margins in N. America indicate cooling
Irregular but progressive trend towards cooling
Several short-lived warming events
Climate records from terrestrial environments
Incomplete
Poorly dated

12. Benthic d18O over last 70 my Benthic foraminifera Not likely altered
Erratic trend towards more positive values
Signal reflects cooling of deep ocean and formation of glacial ice
Both indicate transition from greenhouse to icehouse world

13. Benthic d18O: Temperature or dw
d18O change
Cooling of deep ocean
Growth of ice sheets on land
Storage of 16O-rich water in ice
Both factors influence global cooling
De-convolution allow relative importance of each factor recognized
Sort out the mechanisms controlling cooling

14. Disentangle Temperature and Ice Volume
No ice on Earth mya
d18O increased from –0.75‰ to +0.75‰from mya
Temperature effect only
1.5‰ x 4.2°C ‰-1 = 6°C
Evidence of ice on Earth at 35 mya
Ice volume and d18O unknown
d18O increased from to +3.5‰ from 40 mya to today
About 1‰ can be attributed to ice volume
Temperature increased by 1.75‰ x 4.2°C‰-1 = 7°C
Deep ocean increased 13-14°C over last 55 my

15. Temperature Trends Similar
Overall terrestrial and marine trends are similar
Detailed records differ – regional effect?

16. Deep Ocean Circulation
Deep ocean 55 mya 16°C
Today deep ocean 2°C
Site of deep water formation warm
Changes in circulation affected climate
Changes may have been abrupt
After some threshold was reached
May have remained in one mode while climate changed
Then abruptly changed once a certain threshold was reached

17. Climate Cooling Proxy evidence indicates an erratic cooling
Over both poles and mid latitudes
Roughly equal cooling in first and second half of interval

18. Tectonic Scale Cooling Mechanism?
Lower volcanic CO2 emissions
Increased weathering
Increased ocean heat transport
Tectonic changes
Atlantic widened and Pacific narrowed
India and Australia separated from Antarctica
India and Australia moved to lower latitudes
India collided with Eurasia
Key oceanic gateways open and closed

19. BLAG Hypothesis Depends of global spreading rates
55-15 mya general decrease in spreading
Produce cooling
15 mya to today spreading increased
Produce warming
Consistent with record prior to 15 mya
Inconsistent with record from 15 mya to present
Cannot alone explain cooling

20. Uplift Weathering Hypothesis
To explain cooling, 3 criteria must be met
High elevation terrain today must be unusually large
High terrain must cause unusual amount of rock fragmentation
Fragmentation and exposure must enhance chemical weathering

21. Extensive High Terrain
Many young mountain ranges with uplifted Cretaceous sediments
Tibet and Himalayas of Asia
South American Andes
North America Rocky Mountains
European Alps
Are these uplifted terrains, uniquely high?
Uplift associated with subduction common
Uplift associated with continental-continental collision less common

22. Earth’s High Topography
Only a few regions with elevations above 1 km
Most young tectonic terrains
Exception is E. African plateau

23. India-Asia Collision Formation of Tibetan Plateau
Large geographic region elevated
Initial collision about 55 mya
Uplift continues today
No large continental collisions between mya

24. Elevation on Earth
Most high elevation caused by subduction of oceanic crust and volcanism
Mountain ranges associates with subduction common throughout geologic time
Deep-seated heating and volcanism
East African plateau
Mechanism of uplift not unique to last 55 my
Existence of uplifted terrains like the Tibetan Plateau
Not common through geologic time
Conclude – amount of high elevation terrain is unusually large during last 55 my

25. Physical Weathering High
Does the amount of high elevation terrain result in unusual physical weathering?
Most likely given 10 fold increase of sediment to the Indian Ocean
Steep terrain along southern Himalayan margin
Presence of powerful South Asian monsoon

26. Physical Weathering Unusual?
Incomplete geologic record does not tell us if these deposits are unique
Deltaic deposits can be subducted and/or reworked and redistributed
Rapid deposition of sediments in Indian Ocean indicates rapid influx
Supports uplift weathering hypothesis
No way to determine if physical weathering stronger than in past

27. Chemical Weathering
Global chemical weathering rates difficult to determine
Dissolved ions in rivers clue
Today concentration modified by human activity
Difficult to distinguish ions from hydrolysis and dissolution
Only hydrolysis important on long term
Lots of rivers contribute ions to ocean
Chemical weathering rates in past very difficult to quantify
Need chemical indicator of hydrolysis
Isotopes of strontium and osmium