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.

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.

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

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.

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.

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

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

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

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

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

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

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

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

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

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

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

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.

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).

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?

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

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

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

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.

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.