Lecture 4 Cenozoic Climate Lecture 4 Cenozoic Climate ChangeChange

We are in the midst of an interglacial time. Still, we know We are in the midst of an interglacial time. Still, we know the glaciers will come back. Let’s recall how the Earth’s the glaciers will come back. Let’s recall how the Earth’s climate changed during the Cenozoic. climate changed during the Cenozoic.

Cenozoic CoolingCenozoic Cooling• During the Cenozoic, temperatures

decreased as moving continents diverted warming currents

• During the Cenozoic the poles became much cooler than the equator

Atmospheric circulation Atmospheric circulation By 30By 30oo of movement away from the equator, winds are turned by of movement away from the equator, winds are turned by Coriolis and aligned with equator. The Breaks separate flow into Coriolis and aligned with equator. The Breaks separate flow into 6 cells6 cells

Explain Coriolis

Hadley Cell trades

westerlies

trades

westerlies

Ferrell CellPolar Cell

Gyre CCW

Gyre CW

Surface Currents (Influence Climate)

Note Warm Currents not pastS 60o Latitudes

West pushed flow near equator

East pushed flow near 50 degrees

West pushed flow near equator

East pushed flow near 50 degrees

Winds push currents

NH winds turn to right,NH winds turn to right,Currents caused by windsCurrents caused by winds

WESTERN BOUNDARY CURRENTSMOVE WARM WATER POLEWARD

Western Boundary Currents

• Winds cause water to pile up along the western subtropical sides of major oceans.

• Generate fast-flowing currents that redistribute warm tropical waters toward the poles.

• Gulf Stream, Kuroshio, Brazil currents are “West Side” marine rivers, relatively narrow (less than 100 km across) but deep water masses.

• Flow at speeds of 100 to 200 km/day for thousands of kilometers, from equator to high latitudes

Eastern Boundary CurrentEastern Boundary Current

• Eastern boundary currents (Canary, California, Peru) complete the eastern leg of each gyre

• Wider, carry less water, and move more slowly. • The Canary current, nearly 1,000 km (625 miles)

wide but very shallow• 1/3 water of Gulf Stream and travels at 30

km/day• 2/3 continues as cold deep salty current

North Atlantic Deep Water (NADW) down here

WIND

Changes in the positions of the continents greatly influence average current flow

Thermohaline Conveyor

Wally Broecker

Antarctic Circumpolar CurrentAntarctic Circumpolar CurrentPaleocene to Mid-Eocene

WARM Currents from Tropics

Land in polar latitudes but still warm due Western Boundary Currents

Early Eocene Warm Early Eocene Warm Green River FormationGreen River Formation

Oil Shales

Green River Formation, WyomingGreen River Formation, Wyoming

Tropical Plants and Tropical Fish to High Latitudes

Antarctic Circumpolar CurrentAntarctic Circumpolar Current

5. Worldwide spread of GrassesTolerate cooler and drier climateGrass Herbivores evolve.

3. Mid-Late EoceneSudden Cooling 45 mya

4. Longest continuous Ice SheetsStart in Oligocene

1. Australia pulls away

2.Warm current can’t reach Antarctic shores

Late Eocene Continents moved Late Eocene Continents moved - new currents 60- new currents 60ooS lat.S lat.

AntarcticaMid Eocene40 mya

Tibet raises 38 mya due subduction & volcanics, silica weathering increases, CO2 sink

Begin Tibet uplift

Silicate weathering a CO2 sink

Silicate Weathering as a COSilicate Weathering as a CO22 Sink Sink

• “Another carbon sink is the weathering of mountains and other rock formations formed by plate tectonics, mainly silicate weathering. Carbon dioxide is consumed from silicate weathering as seen in this equation: …”

• CaSiO3+ 2CO2 + 2H2O => CaCO3 + SiO2 + CO2 + 2H2O

quoted here:Wollastonite forms when carbonate rocks are subjected to high temperature and pressure in the presence of silica bearing solutions

Early Pliocene Early Pliocene Central and South America not connected.Atlantic and Pacific same salinity

5.5 mya

Gulf Stream

Land in polar latitudes but Arctic still warm due Gulf Stream

Late Pliocene - Gulf stream SaltierLate Pliocene - Gulf stream Saltier

1. 3.5 mya Subduction, Volcanic Arc,Isthmus of Panamaclosed, North Atlantic isol.,higher salinity, dense coolwater sinks before it reaches Arctic, polar sea freezes

Late Pliocene

Sudden Cold & Dry

2. Caused Formation of the modern Gulf Stream Current in the Atlantic

3. Dramatic cooling, dry in Mediterranean dries out thick evaporites

The cause of the Panama land was aVolcanic Island Arc that formed above a subduction zone.

EoceneEocene

•Mammals the dominant land animals. •Earliest giant forms of mammals•Many forest plants, freshwater fish, and insects that were much like those today.

Tapir Heptodon browsed not far from the shores of a lake.

Coryphodon, with its short stock limbs and 5-toed hoofed feet, closely resembled a tapir.

http://www2.nature.nps.gov/geology//parks/eocene.htm

Mostly warm (56 - 37 million years ago)

DiatrymaDiatryma

•The climate became cooler and drier. •More temperate forests, soft grasses •Late Oligocene, savannas (grasslands & woodlands)•Some mammals become grazers. •Modern groups (dogs, cats, horses, pigs, camels, and rodents) rose to new prominence.

Groves of giant redwood trees were found throughout western North America. Changes in climate were responsible for the shrinking range of the redwood forests.

Oreodonts, a group of sheep-like animals, were successful in the Eocene and Oligocene but by the end of the Miocene had completely died out.

Oligocene ( cooling 37-23 million years ago)

BRONTOTHERIUM

http://www.prehistory.com/bronto.htmhttp://www2.nature.nps.gov/geology//parks/pliocene.htm

• Abundance of mammals peak in Miocene. •Forests and savannas persisted in some parts of North America; treeless plains expanded where cool, dry conditions prevailed. Many mammals adapted for prairie; grazers, runners, and burrowers. •Large and small carnivores evolved to prey on these plains-dwellers. •Great intercontinental migrations occurred throughout the Miocene• Animals entering and leaving North America.

Chalicothere Moropus

Menoceras, rhino

earliest true dogs Daphaenodon

Dinohyus, scavenger hog

Stenomylus, camel

Miocene (began 24 million years ago Grasses widespread)

Silica Grasses!High-crown teeth

During the Late Tertiary, temperatures cooled further. Colder air cannot hold as much water, and mid-latitude climates became drier. Trees need great amounts of water, and cannot survive decades of drought. Grasses, on the other hand, can tolerate long periods of drought, and some grasses have a photosynthetic pathway that conserves water, the C4 pathway. Grasslands replaced many forests. Trees retreated to wetter areas, such as the floodplains of rivers. Larger herbivores with taller unrooted teeth evolved to eat silica imbedded grasses.

Grasses prevent gully erosion, Bloom p 51r p2

• Cenozoic Orogenic activity concentrated in two areas– Alpine-Himalayan belt deformation began in the Mesozoic and remains geologically

active. Isolation of Tethys to form the modern Mediterranean Sea

– circum-Pacific belt deformation occurred throughout the Cenozoic– Subduction of the Farallon – Pacific MOR

Cenozoic CoolingCenozoic CoolingPanama Forms

Southern Ocean forms

Glaciers over North!After Figure 4-1 of Bloom

PT + Milankovitch Cycles PT + Milankovitch Cycles

Cycles every 100,000 years

The energy of solar radiation drops off as the square of the distance.Further away = Not as hot => cool summer, warm snowy winter => glaciers grow

Furthest away in NH Summer - cool

summerClosest in WinterWarm Wet Winter

41,000 years

Cold Dry Winter, little snowfall Hot Summer, winter snow melts

Warm Wet Winter, abundant snow Cool SummerSnow doesn’t melt

High latitude getting more sunlight in summerSnow all melts

High latitude getting less sunlight in summer

High latitude getting more sunlight in winter

High latitude getting less sunlight in winterToo cold for much precipitation

GLACIAL

INTERGLACIAL

Present tilt 23.5 degrees

Water molecules containing an oxygen of the lighter 16O isotope are more likely to evaporate from the surface of the ocean and can be frozen into continental ice sheets. This causes the oceans to become enriched in the 18O isotope left behind. This means that glacial times can be recognized from fossil shells containing oxygen from seawater.

How Oxygen’s stable isotopes can measure past temperatures

The Late Tertiary and Quaternary oxygen

isotope record measured in marine fossil shells

Evap. water and CO2 during glacial timeremoves 16O to glacier ice leaving 18O in oceans for CaCO3 shell

cf Figure 4.7 of Bloom

Foraminifera tests - Ice AgeForaminifera tests - Ice Age

Evap. water and CO2 during glacial

removes 16O to glacier ice leaving 18O in oceans for CaCO3 shell

Also spiral direction & diversity dep T

Nebraskan

Kansan

Illinoian

Wisconsinan

> 30 pulses in 4 or so major groups

warm cold

Ice Sheet 20 kya then temporary warmingIce Sheet 20 kya then temporary warming

Scoured 30 M below sea-level

Max Glacier Distribution 20,000 yaMax Glacier Distribution 20,000 ya

Maximum glaciation occurs at coincidence of astronomical cyclesif land in polar latitudes

Global Temperatures Cycle, largest Global Temperatures Cycle, largest 100,000 Year (orbit eccentricity)100,000 Year (orbit eccentricity)

Smaller signals about 25K and 41K

Interglacials get really WARM and vary in durationInterglacials get really WARM and vary in duration

Wisconsinan

Notice Interglacials get much warmer

NOW PAST

Effects of GlaciationEffects of Glaciation

• Change Climate – increase precipitation

locally - pluvial lakes

• Depress continents & lateral rebound

• Drop sea-level: alter coastlines

• Form continent-wide Dams– Divert streams – Ohio and Missouri rivers

Formation of Terraces due to Crustal ReboundFormation of Terraces due to Crustal Rebound

Lowered Sea-level exposed continental shelfLowered Sea-level exposed continental shelf

Lowered Sea-level - Land bridgeLowered Sea-level - Land bridge

Air bubbles trapped in glacial ice reveal the composition of the Pleistocene to Recent atmosphere.

Uppermost warm in picture is the current interglacial, the Holocene

Cold pulse from about 1300 to 1850 AD Cold pulse from about 1300 to 1850 AD (The so-called “Little Ice Age”)(The so-called “Little Ice Age”)

Climate has been warming since then.Climate has been warming since then.

Athabaska Glacier, Columbia Icefield, W. Canada

Discussion: Global Warming

Worldwide melting, Worldwide melting, regardless of cause, releases regardless of cause, releases COCO22 and H and H22O and exposes O and exposes

dark land. The atmosphere dark land. The atmosphere receives and holds more heat, receives and holds more heat, and temperatures rise.and temperatures rise.

• 1. 1. Convection currents in the lithosphere move the Convection currents in the lithosphere move the continents.continents.

2. Continent positions deflect ocean convection 2. Continent positions deflect ocean convection currents and change ocean basin salinity. These currents and change ocean basin salinity. These change weather => climatechange weather => climate 3. 3. We are currently in an interglacial because our We are currently in an interglacial because our spin axis tilt is 23.5 degrees, headed toward 24.5.spin axis tilt is 23.5 degrees, headed toward 24.5.

4. It will get much warmer as the interglacial 4. It will get much warmer as the interglacial continues, but then COLDERcontinues, but then COLDER

Summary

Temporary WarmingTemporary Warming• Interglacial warming releases greenhouse gas – Interglacial warming releases greenhouse gas –

Positive feedbackPositive feedback• A warmer system is more energeticA warmer system is more energetic• We expect stronger storms, less weather We expect stronger storms, less weather

predictability predictability • We expect pole-ward shifts in climatesWe expect pole-ward shifts in climates

• Eventually the interglacial will end, and then Eventually the interglacial will end, and then another glacial time will control the surface of another glacial time will control the surface of earth.earth.

Super Volcano WintersSuper Volcano Winters• About 72000 years ago a huge rhyolitic magma on About 72000 years ago a huge rhyolitic magma on

Indonesia erupted. Toba Lake is the large caldera Indonesia erupted. Toba Lake is the large caldera that remains. A worldwide ash fall occurred, three that remains. A worldwide ash fall occurred, three times thicker than any other global Pleistocene ash times thicker than any other global Pleistocene ash fall. Some workers think thatfall. Some workers think that SOSO22 got into the got into the

stratosphere, forming Hstratosphere, forming H22SOSO44. Sunlight was blocked . Sunlight was blocked

around the world, and plants died.around the world, and plants died.• Studies of Mitochondrial DNA in humans reveal that Studies of Mitochondrial DNA in humans reveal that

humanity suffered a near extinction event about that humanity suffered a near extinction event about that time. All humans are descended from a few thousand time. All humans are descended from a few thousand mothers.mothers.

http://www.kean.edu/~csmart/Observing/Lectures/Toba/Toba,%20Sumatra,%20Indonesia.htm