1. UNDERC INTRODUCTION #1: A REGION SHAPED BY GLACIERS
This aerial view of UNDERC demonstrates how the landscape was shaped by glaciers during the Pleistocene – flat and lakes.

2. MULTIPLE PERIODS OF GLACIATION
PLEISTOCENE: 2 million years ago – 10,000 years ago
4 major glaciations in North America (~ 14 advances and retreats in last 1 million years)
(However, probably continental glaciations for the past 10 million years)
The Pleistocene was a period of 2 million years that had recurrent continental glaciations and interstadial periods of warming when the glaciers either receded or disappeared. The glaciers differed in severity (how far south they advanced), which obliterated the boundaries of earlier less severe glaciations.

3. WHAT CAUSES GLACIATION?
Snows did not melt in northern regions during summer
4 – 7oC decline in mean annual temperature (change in δ18O)
Pleistocene
Continental glaciations occur when more snow is deposited in the winter than can melt off in the summer. The accumulation of this snow becomes ice and moves southward under its own weight. We know that glaciations occurred when mean annual temperature decline by 4 – 7oC. The temperature changes are measured using oxygen isotopes trapped in ice cores (more negative isotopic value means colder). Laurentide or Wisconsin refers to the last major glaciation.
Laurentide

4. WHAT CAUSES GLACIATION?
Sea-level fluctuates as water forms glaciers
Gravitational effects of planetary bodies perturb Earth’s orbit which varies distribution of solar radiation (Milankovitch Cycles)
Glaciation leads to reduced sea-levels (water tied up in glaciers), which enhances the temperature effects by eliminating the ameliorating effects of large bodies of water. However, glaciation is thought to occur due to changes in the earth’s orbit and the angle of its axis, which reduce the amount of solar radiation striking the earth.

5. MOST RECENT GLACIAL EXTENT
Here we see the extent of glaciers at the last glacial maximum and the reduction in sea-level increasing the terrestrial area.

6. Extent of Continental Glaciation
Anchorage
Juneau
Churchill
Here is maximum glaciation of the last glaciation in North America. We are looking at a sheet of ice over a mile thick.
Calgary
Quebec
Seattle
Winnipeg
Ottawa
New York
St. Paul
Cleveland
Chicago
San Francisco
Denver
St. Louis

7. GLACIAL ADVANCE AND RETREAT (Wisconsin Glaciation – Laurentide
This internet link exhibits the glacial movement of the last glaciation.

8. Glacier Cross Section New snow Ice crystals Compressed crystals
This depicts the cross section of a glacier illustrating how the weight of higher levels change snow to ice and how the ice crystals change under pressure to allow the glacier to move.
Flowing crystals

9. Inland Lakes Resulting from Melt Water
Anchorage
Juneau
Churchill
Quebec
As the glacier recedes, it melts and creates flooded areas –
Lakes and large regions of outwash.
Calgary
Ottawa
Seattle
Winnipeg
New York
St. Paul
Cleveland
Chicago
San Francisco
Denver
St. Louis
Miami

10. Formation of Kettle lakes
Ice margin
Ice blocks in outwash plain
Continental
Glacier
Kettle lake at ice contact on terminal moraine
Lake in irregular ground moraine
Kettle lakes in outwash plain
Kettle in drift
Other types of lakes are formed. Kettle lakes arise when the glacier leaves behind buried hunks of ice which create a depression when they melt that fills with water.
Ice
Lake

11. Formation of Permafrost Lakes
Glaciation can create lakes when the ground is so frozen (permafrost) that water cannot drain out of a depression.
No Permafrost

12. Arctic Permafrost Lakes (Tundra, Northwest Territories, Canada)
These are permafrost lakes in the arctic tundra. What kind of lakes are at UNDERC?

13. Land O’ Lakes Aquatic Habitats Are Glacial Products
35 lakes and bogs
2 streams
many forest and wetland habitats
Bergner
Bay
The UNDERC landscape was scoured by the glaciers (little topography) and left kettle lakes.
Long

14. TERRESTRIAL REMNANTS Glacial drift (deposits of earth and rock)
till = ice-laid outwash = water-laid
Moraines (till deposited in ridges)
We can see telltale marks of the glaciers –
till is rocky deposits left behind by the glacier (UNDERC gravel pit)
outwash is lighter deposits left behind by glacial melt water
moraines are ridges of till left at the edges of glaciers by their advances and retreats

15. TERRESTRIAL REMNANTS ERRATICS: STRIATIONS: Other remnants are—
erratics are large rocks deposited many miles from the place of origin
striations are scrapes in rocks when glaciers carry debris that acts as an abrasive on bedrock

16. TERRESTRIAL REMNANTS ESKER – subglacial streams that deposited
gravel to now
appear as a low
winding ridge.

17. GLACIAL ENVIRONMENTS
The Pleistocene was a time of diverse and amazing large mammals that are extinct today—
Cervalces (moose stags)
mammoths – grazers
mastodons – browsers
We will revisit their extinction next lecture.

18. HOW ARE ENVIRONMENTS RECONSTRUCTED?
We know about Pleistocene environments by taking cores from ponds/lakes where material has been deposited and undisturbed for long periods. The pollen from plants are identified and quantified in the cores. The deeper in the core the older the sample. Actual dating can be conducted using C14 dating (radioactive decay). Pollen is assumed to come from surrounding plant communities. Climates are attributed by assuming that the plant species then occurred in similar environments where we see them today (uniformitarianism).

19. TODAY’S ENVIRONMENT
The UNDERC environment today contains very different plants and animals than occurred there as the last glaciation receded. Why is it important to say receding?

20. HOW DID THINGS CHANGE? Pollen Viewer
Here is an internet link showing how different tree species moved with the last glaciation. Look at several species that you know. Look at several species that you know live together (associated) today.
Pollen Viewer

21. Mix Of Different Tree Species Since Glaciation
We see different species assemblages in the past than today.
Mix Of Different Tree Species Since Glaciation

22. Disequilibrium View of Forests Since Glaciation
We know that species found together today did not necessarily occur together in the past. One explanation is that the associations that we see today are simply a product of how fast different species have been able to migrate north after the glaciation from their refuges.
Disequilibrium View of Forests Since Glaciation

23. Dissimilarity in Tree Composition and Climate
The internet maps that you examined indicate that the assemblages of species since peak glaciation are a result of each species’ ability to cope with different environmental conditions. Past environmental conditions were not the same as today – different temperatures, precipitation, season length, which allowed different species to be assembled together in an area than we see today where the species occur.

24. CHANGE CONTINUES EVOLUTIONARY AND GEOLOGICAL CHANGE (inherent)
ECOLOGY OF AQUATIC HABITATS (inherent)
ECOLOGY OF TERRESTRIAL HABITATS (inherent)
HISTORICAL CHANGES WITH HUMANS
(Native Americans and Europeans) – environmental history
The environment is not constant but continually changing – we have examined evolutionary and geological changes here. In coming weeks we will look at changes that are more short term in aquatic and terrestrial habitats. We will examine next week the changes brought about by humans.