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

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

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

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)

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 99-17 are same age. Lines connect species common to both sites. Diagenetic calcite from Site 523.

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

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

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

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

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

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

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

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

Disentangle Temperature and Ice Volume No ice on Earth 70-40 mya d18O increased from –0.75‰ to +0.75‰from 55-40 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 +0.75 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

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

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

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

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

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

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

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

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

India-Asia Collision Formation of Tibetan Plateau Large geographic region elevated Initial collision about 55 mya Uplift continues today No large continental collisions between 100-65 mya

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

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

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

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