Outline 23:

The Ice Ages-Cenozoic

Climatic History

Continental Glacier in Antarctica

Valley Glaciers in Alaska, note the moraines

Valley Glaciers in Alaska, note the moraines

Mendenhall Glacier, Juneau, Alaska

Prince William Sound, Alaska

Glacier Bay National Park, Alaska

Ice Ages in Earth History

• Late Cenozoic: last 5 MY

• Pennsylvanian and Permian: 300 MY ago

• Ordovician: 450 MYago

• Late Proterozoic: 700 MY ago

• Early Proterozoic: 2200 MY ago

Phanerozoic Climate Change

Late Proterozoic Glacial Deposits

and Striated Bedrock, North Africa

Glacial Striations

Pleistocene Glacial striations on bedrock, Alaska

Definitions

• Ice Age or Ages: whenever there are

glaciers at one or both poles during

earth history.

• Glacial stage: when glaciers are very

extensive during an ice age.

• Interglacial stage: when glaciers are

less extensive during an ice age.

Cenozoic Climatic History

• Paleocene and Eocene: warm, tropical

climate, no ice at the poles.

• Oligocene: ice starts to form on

Antarctica as the Circum-Antarctic

Current forms. This leads to Albedo

changes causing more cooling.

Circum-Antarctic Current

• Flows clockwise around Antarctica;

driven by westerly winds.

• Formed as South America, Africa, and

Australia moved away from

Antarctica.

• It is the fundamental cause of the

Cenozoic ice ages.

Eocene

Oligocene

Earth’s Albedo

• Albedo refers to total reflectance of

sunlight from the Earth.

• Ice: >90% reflectance

• Land: 30-70% reflectance

• Water: 20%

Cenozoic Climatic History

• Miocene: glaciers on Antarctica reach

maximum size 5 MY ago. Sea level

falls 150 ft. causing Mediterranean Sea

to dry up. Deep oceans cool to near

freezing causing cooling of Arctic

waters. Earth’s albedo continues to

change.

Cenozoic Climatic History

• Pliocene: first glaciers in Arctic;

earth’s albedo continues to change.

• Pleistocene: maximum glaciation in

Northern Hemisphere. About 20

cycles of glacial-interglacial stages.

We are currently in an interglacial

stage.

Ice Age Facts

• Ice Cover of Land

– 10% today

– 30% during last glacial stage

• Ice Thickness

– up to 9,000 ft. on Greenland

– up to 11,000 ft. on Antarctica

Coastline

changes

between

glacial and

interglacial

stages

Eastern Beringia during the last glacial maximum with eustatic

sea level lowering of 120 m. The region was largely unglaciated

with the exception of local uplands that supported alpine glaciers.

(GSA Today, August 2009)

Animals, including humans, walked from Asia to North

America during the Pleistocene glacial stages.

Scientific

American,

Nov. 2011

Two Routes: Sea starting

16,000 years ago.

Land starting

15,000 years ago.

Modern Environments

Glacial Environments

Ice Age Facts

• Sea Level Changes:

– If all modern ice melted, sea level

would rise 200 ft. to pre-Ice Age

levels.

– During maximum glaciation sea

level was 400 ft. lower.

– Range of possible sea level changes

= 600 ft.

Ice Age Facts

• Isostatic Depression and Rebound

– Currently, the center of Greenland is

1,000 ft. below sea level.

– Hudson Bay and Baltic Sea areas

have rebounded 800 ft. since last ice

age ended 10,000 years ago.

Glacial rebound

in Canada.

Meters of uplift

since the glaciers

melted 6000

years ago.

Glacial rebound

in Scandinavia.

Mm per year

during the 20th

Century.

Lakes that

formed in the

western U.S.

during the last

glacial stage

when the climate

was wetter.

Bonneville Salt Flats: Dried up Pleistocene lake bed

Ice Age Facts

• The Great Lakes were carved by

glaciers.

• The ice sheets were larger in North

America than in Eurasia. Size of

sheets depends on amount of snowfall

and rate of melting.

Terminal morraines in North America

WVU

Ice-carved lakes: Finger Lakes, NY

14,000 yrs 12,000 yrs

10,000 yrs

Exit Glacier, Seward, Alaska is receding

End moraine of Exit Glacier, Seward, Alaska

Maximum North

American ice

coverage and dates

of melting.

Causes of Glacial Cycles: The

Milankovitch Theory

• Changes in the Earth’s orbital

parameters causes climate extremes of

northern hemisphere summers.

• Cool northern hemisphere summers

lead to glaciation as less winter ice

melts.

• Cold winters by themselves don’t

cause glaciation.

Causes of Glacial Cycles: The

Milankovitch Theory • Orbital Parameters:

– eccentricity: the shape of the orbit

– tilt of Earth’s axis: ranges from 22.1-24.5 degrees, currently 23.5; also called obliquity

– perihelion: time of the year when the Earth is closest to the sun. Changes due to precession of the earth’s axis.

Variation in the Earth’s orbital parameters is

caused by the gravitational pull of Jupiter.

(Exaggerated)

Warmer Cooler

More tilt,

more seasonal

extremes.

If the Earth is

closer to the

sun at the

Equinoxes, it

will be cooler

at the Solstices

because of the

elliptical orbit.

Deep Sea Record of

Temperatures

• The ratio of O-18 to O-16 in deep

water sea shells indicates cycles of

temperature change.

• These cycles match the predicted

Milankovich cycles. The three cycles

overlap to create a complicated pattern.

Oxygen isotopic

composition of

foraminifera shells

during the Ice Age

1

2

3

4

5

6

7

Glacial

stages

8

Cold Warm

1 mm

Foram shells

recovered

from oceanic

sediments

1 2 3

4

Glacial stages

Antarctic Ice

Core

The greenhouse gas, CO2, is increasing rapidly.

Data from ice cores.

1 2

3 4

The greenhouse gas, CO2, is increasing rapidly.

Data from ice cores during the last 1000 years.

Glaciers are retreating worldwide due to

global warming. 1978 margin (2001 photo)