lecture 4 cenozoic climate change
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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
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