Lecture 4 Cenozoic Climate Change
We are in the midst of an interglacial time. Still, we know
the glaciers will come back. Let’s recall how the Earth’s
climate changed during the Cenozoic.
Cenozoic 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
By 30o of movement away from the equator, winds are turned by
Coriolis and aligned with equator. The Breaks separate flow into
6 cells
Polar Cell
Ferrell Cell
westerlies
Hadley Cell
trades
trades
westerlies
Explain Coriolis
Surface Currents
(Influence Climate)
NH winds turn to right,
Currents caused by winds
Winds push currents
East pushed flow near 50 degrees
Gyre CW
West pushed flow near equator
West pushed flow near equator
Gyre CCW
East pushed flow near 50 degrees
WESTERN BOUNDARY CURRENTS
MOVE WARM WATER POLEWARD
Note Warm Currents not past
S 60o Latitudes
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 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
WIND
North Atlantic Deep Water
(NADW) down here
Changes in the positions of the continents greatly influence average current flow
Wally Broecker
Thermohaline Conveyor
Antarctic Circumpolar Current
Paleocene to Mid-Eocene
WARM Currents from Tropics
Land in polar latitudes but still warm due Western Boundary Currents
Early Eocene Warm
Green River Formation
Oil Shales
Green River Formation, Wyoming
Tropical Plants and Tropical Fish
to High Latitudes
Antarctic Circumpolar Current
3. Mid-Late Eocene
Sudden Cooling 45 mya
2.
Warm current
can’t reach
Antarctic shores
4. Longest continuous Ice Sheets
Start in Oligocene
5. Worldwide spread of Grasses
Tolerate cooler and drier climate
Grass Herbivores evolve.
1. Australia pulls away
Late Eocene Continents moved
- new currents 60oS lat.
Silicate weathering a CO2 sink
Begin Tibet uplift
40 mya
Antarctica
Mid Eocene
Tibet raises 38 mya due subduction & volcanics, silica weathering increases, CO2 sink
Silicate Weathering as a CO2 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
Central and South America not connected.
Atlantic and Pacific same salinity
5.5 mya
Land in polar latitudes but Arctic still warm due Gulf Stream
Late Pliocene - Gulf stream Saltier
1. 3.5 mya Subduction, Volcanic Arc,
Isthmus of Panama
closed, North Atlantic isol.,
higher salinity, dense cool
water sinks before it
reaches Arctic, polar sea freezes
Sudden Cold & Dry
Late Pliocene
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 a
Volcanic Island Arc that formed above
a subduction zone.
Eocene
Mostly warm (56 - 37 million years ago)
•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.
Diatryma
Oligocene ( cooling 37-23 million years ago)
•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.
http://www.prehistory.com/bronto.htm
Groves of giant redwood
trees were found
throughout western North
America. Changes in
climate were responsible
for the shrinking range of
the redwood forests.
http://www2.nature.nps.gov/geology//parks/pliocene.htm
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.
BRONTOTHERIUM
Miocene (began 24 million years ago Grasses widespread)
• 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.
Stenomylus, camel
Chalicothere
Moropus
Menoceras,
rhino
Silica Grasses!
High-crown teeth
Dinohyus, scavenger hog
earliest true dogs
Daphaenodon
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 Cooling
Southern Ocean forms
Panama Forms
After Figure 4-1 of Bloom
Glaciers over North!
PT + Milankovitch Cycles
Furthest away in NH
Summer - cool
summer
Closest in Winter
Warm Wet Winter
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
Cycles every 100,000 years
Present tilt 23.5 degrees
High latitude getting more sunlight in winter
GLACIAL
Warm Wet Winter,
abundant snow
Cool Summer
Snow doesn’t melt
High latitude getting less sunlight in summer
High latitude getting less sunlight in winter
Too cold for much precipitation
INTERGLACIAL
Cold Dry Winter, little snowfall
Hot Summer, winter snow melts
High latitude getting more sunlight in summer
Snow all melts
41,000 years
How Oxygen’s stable isotopes can measure past temperatures
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.
The Late Tertiary and
Quaternary oxygen
isotope record measured
in marine fossil shells
Evap. water and CO2 during glacial time
removes 16O to glacier ice leaving
18O in oceans for CaCO shell
3
cf Figure 4.7 of Bloom
Foraminifera tests - Ice Age
Wisconsinan
Illinoian
> 30 pulses in 4 or
so major groups
Kansan
Nebraskan
Evap. water and CO2
removes 16O to
18O in oceans
warm
Also spiral direction & diversity dep T
during glacial
glacier ice leaving
for CaCO3 shell
cold
Ice Sheet 20 kya then temporary warming
Scoured 30 M below sea-level
Max Glacier Distribution 20,000 ya
Maximum glaciation occurs at coincidence of astronomical cycles
if land in polar latitudes
Global Temperatures Cycle, largest
100,000 Year (orbit eccentricity)
NOW
PAST
Smaller signals about 25K and
41KNotice Interglacials
get much warmer
Wisconsinan
Interglacials get really WARM and vary in duration
Effects 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 Rebound
Lowered Sea-level exposed continental shelf
Lowered 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
(The so-called “Little Ice Age”)
Climate has been warming since then.
Discussion: Global Warming
Worldwide melting,
regardless of cause, releases
CO2 and H2O and exposes
dark land. The atmosphere
receives and holds more heat,
and temperatures rise.
Athabaska Glacier, Columbia Icefield, W. Canada
Summary
• 1. Convection currents in the lithosphere
move the continents.
2. Continent positions deflect ocean
convection currents and change ocean basin
salinity. These change weather => climate
3. We are currently in an interglacial
because our spin axis tilt is 23.5 degrees,
headed toward 24.5.
4. It will get much warmer as the
interglacial continues, but then COLDER
Temporary Warming
• Interglacial warming releases greenhouse
gas – Positive feedback
• A warmer system is more energetic
• We expect stronger storms, less weather
predictability
• We expect pole-ward shifts in climates
• Eventually the interglacial will end, and
then another glacial time will control the
surface of earth.
Super Volcano Winters
• About 72000 years ago a huge rhyolitic magma
on Indonesia erupted. Toba Lake is the large
caldera that remains. A worldwide ash fall
occurred, three times thicker than any other
global Pleistocene ash fall. Some workers think
that SO2 got into the stratosphere, forming
H2SO4. Sunlight was blocked around the world,
and plants died.
• Studies of Mitochondrial DNA in humans reveal
that humanity suffered a near extinction event
about that time. All humans are descended from
a few thousand mothers.
http://www.kean.edu/~csmart/Observing/Lectures/Toba/Toba,%20Sumatra,%20Indonesia.htm