Glaciations

Glaciations

A period when global climate cools significanltly

What happens in glaciations?

Continental ice sheets expand, sea level drop, ecosystems shift.

Repeated glaciations in the last ___ million years

2.6 my

~___ major glaciations in the past million years

~10

major glaciations in the last _

3, 150,000 years

Last Glacial Maximum(LGM) was ___ years ago.

~18,000 ya

Last Glacial Maximum (LGM)

Sheets of ice, sea level drop ~120m

Causes of Glaciation

Linked to variation in Earths Orbit, Eccentricity, Tilt, Orbital precession

Linked to variation in Earths Orbit

Cyclic variation Affects solar heating, Milankovitch Cycles

Eccentricity

Shape of orbit

Eccentricity happen when ..

Orbits shifts between circular and elliptical

Eccentricity was ____

~95,000-100,000 years ago

Eccentricity affects the…

Distance to the sun

More elliptical:

Cooler summers, ice sheets grow, ice and snow don’t melt

Obliquely - Tilt

Earth can slightly shift how tilted it is

Tilt was roughly…

~ 41,000 years ago

Larger Tilt

Stronger seasons, warmer summers (more melting), cooler winters (more snow, cannot offset melting)

Smaller tilt

Cooler summers, glaciers grow

Precision - Wobble

Changes timing of seasons

Wobble - changing timing of seasons

Determines which hemisphere leans towards or away from the sun

If cooler summers in northern hemisphere,…

see ice sheets survive and glaciation increases

Wobble occurred…

~22,000-26,000 years

Wobble comes from..

gravitational pull from sun and moon

Cycle Type

Procession, obliquity (tilt), eccentricity

Procession - Period

~22,000 yrs

Procession - What it changes

Wobble of Earth’s axis

Procession - Impact

Alters timing of seasons

Obliquity (tilt) - Period

~41,000 years

Obliquity (Tilt) - What it changes

Axial tilt angle

Obliquity (Tilt) - Impact

Controls seasonal contrast

Eccentricity - Period

~95,000-100,000 years

Eccentricity - what it changes

Shape of orbit

Eccentricity - Impact

Controls distance to Sun

Why Northern Hemisphere?

Has most of continental land mass

Has most of continental land mass

Ice grows on land, not ocean. Cool summers = ice age growth. Warm summer = ice age retreat.

Effects of Last Glaciation - Land

5-7C cooler on average

Effects of Last Glaciation - Water and air

2-3C cooler on average

Effects of Last Glaciation - Ice Sheets

Massive ones covered N hemisphere

Effects of Last Glaciation - Great Lakes

Shaped by glacier movement

Effects of Last Glaciation - Sea Levels

Drastically lowered, ~430 ft, Water became locked in glacial ice, Exposed large portion of continental shelf

Effects of Last Glaciation - Land Bridge Formation - Beringia

Allowed humans to migrate into North America and horses to cross into Asia

Effects of Glaciation - Doggerland

Connected Europe and Britain. English channel was land. Ireland remained isolated. Large costal pains created new habitat (Megafauna)

How do glaciers change environments?

Glaciers can move seidment

Glaciers can move sediment

Take from one area, and move it with the glaciers as it moves. Increase erosion. Increase freeze-thawing erosion

Glaciation: Shifts in Rain Belts

African rain belt shifted south. Congo rainforests became sand dunes. lake Tanganyika 400m shallower.

LGM

Last Glacial Maximum. 18,000 years

Lake Tanganyika

Shrunk into three separate basins. Isolated promoted speciation (Why more fish than in any other lakes now)

Post Glacial Climate - Rain returns

~10,000-7,000. Monsoons strengthen. Lakes became much deeper.

Post Glacial Climate - Expansion of

Wetlands, Megafauna habitats, Early human population boom

Post Glacial Climate - 5,000 years ago

Increase moisture in SE North America. Arizona greener, less desert. Indigenous settlements thrived.

Shifting Biotic Ranges

Climate zones moved during glacial cycles

Climate zones moved - Changed migration patterns

Wildebeest following the shifting grasslands, Hummingbirds tracked seasonal flowering shifts

Climate zones moved - Changed where plants could survive

Pushed trees and vegetation towards equator, Shifted organisms to lower elevation

Shifting Biotic Ranges - What about non mobile organisms?

Local extinctions. Soil microbes/things that don’t move fast enough

North American Forests

Mountains run north south. Forests could expand south ahead of moving glaciers

Europe Forests

Mountains run east west. Forests cannot shift south, they get trapped by mountains. Trapped between ice sheets and mountains.

North America - Mountain Orientation

North-South ranges (Appalachians, Rockies)

North America - Forest ability to move

Trees migrated south ahead of glaciers

North America - Glacial survival

Large refuge zones

North America - Tree diversity today

~600 species

Europe - Mountain orientation

East-West ranges (Pyrenees, Alps, Carpathians)

Europe - Forest ability to move

Trees trapped between ice sheets and mountains

Europe - Glacial survival

Small, fragmented refuges

Europe - Tree diversity today

~85 species

How this shapes where organisms live

Climate, Biota, Time, history

How this shapes where organisms live - Climate

physical factors

How this shapes where organisms live - Biota

Competition, predation, herbivory, mutualism

How this shapes where organisms live - Time

Successional stage, disturbance frequency

How this shapes where organisms live - history

Continental drift, glaciations, extinctions, colonization route

During glacial maximums, species ranges typically shift where?

Towards the equator

Why does Europe have fewer species than North America?

During glaciation, Europe trees were trapped by the E-W mountain ranges, so thy couldn’t escape the moving glaciers