Glaciation part 1

Question 1

Glacier

Answer 1

A perennial mass of ice that moves or is capable of movement over land (movement due to gravity or compression force- needs at least 50 m)

Question 2

Pleistocene glaciations

Answer 2

20 glacial advances in the past 2 million years

Question 3

Causes of glaciation

Answer 3

Climatic cooling
Milankovitch cycles
Positive Feedback

Question 4

Climatic cooling driven by

Answer 4

Continental coalescence (huge continental areas) (not enough time)
Continental drift into far souther latitudes (near south pole) (not enough time)
Variation in solar output (stable during this time)
Volcanic activity resulting in particulate matter in the atmosphere (not associated with pleistocene)

Question 5

Milankovitch Cycles

Answer 5

Variation in the earth’s elipticallness in orbit around sun, axial tilt, and precession comprise three dominant cycles.
The three cycles impact the seasonality and location of solar energy around the earth.

Question 6

Milankovitch Cycles: eccentricity

Answer 6

Shape of the Earth’s Orbit around the sun changes. When orbit is most ellipitcal the earth recieves 20-30% more solar radiation at the perihelion than at the aphelion. Today the orbit is at low eccentricity (i.e less ellipticallity)
Cyclic period: 100, 000 years
Perihelion- closest point
Aphelion- farthest point

Question 7

Milankovitch Cycles: Axial tilt (obliquity)

Answer 7

Inclination of the Earth’s title in relation to its plane of orbit around the sun.
Minimum tilt solar radiation is more evenly distributed across seasons
Hypothesis- minimum tilt could promote growth of ice sheets (more snow with warmer winter, less opportunity to melt in cooler summer)
Max tilt- 24.5o
Min tilt- 22.1o
Current- 23.5
Cyclic period- 41 000 years

Question 8

Milankovitch Cycles: Precession

Answer 8

When axis is tilted towards Vega, the position of the Northern Hemisphere winter solstice coincides with the aphelion and the summer solstice with the perihelion resulting in greater seasonal contrasts.
Currently, Earth experiences perihelion close to the winter solstice. (i.e. lesser seasonal contrasts)
Cyclic period: 22 000 years

Question 9

Milankovitch Cycles in combination

Answer 9

When the three different cycles combine they are responsible for major changes in the Earth’s climate.

Question 10

Growing Ice sheets

Answer 10

eliminate plant/animal life over large areas
Natural production of greenhouse gases decline
more white surfaces increase reflection of light energy

Question 11

Retreating ice sheets

Answer 11

Increases plant/animal life
Increases production of greenhouse gases
albedo decreases

Question 12

Characteristics of the Pleistocene glaciations

Answer 12

Most of the glaciations had the same range and extent
Glacial sheets consisted of massive ice formations up to 4 km thick and covered up to one third of Earth’s land mass
Much more extensive in the N hemisphere (more land mass and more continental climate)
Greater extent in NA than Eurasia (ex, last glaciation 80% of ice was in NA)

Question 13

Changes Associated

Answer 13

1) Elimination of Terrestrial habitat (ice covered 33% of terrestrial area last glaciation, but some land opened up due to falling sea levels)
2) Shifts in Climate regimes
3) changes in sea level

Question 14

Glacial Refugium

Answer 14

-An area that has remained relatively unchanged while surrounding areas are glaciated and which has thus served as a refuge for species displaced by the glacial advance. -Caused by glaciation
Some refugia: beringian (alaska) , columbia (oregon), atlantic , Mississippi
-are centers of diversity or centers of endemism (evidence that these areas provided safe retreat during glaciation)

Question 15

Microrefugia

Answer 15

glacial refugia of smaller geographical area that may have been important to fewer species than larger main refugia for survival during glaciation
Three types: distal/remote, widespread/diffuse, proximal or ecotonal
Ex: Lemming range across eastern beringia and Canada.
Eastern refugia had several mini refugia everywhere
This is also evident because fossils occur in places where there were glaciers

Question 16

Proglacial lakes (lakes that form just beyond frontal margin of advancing or retreating glacier)

Answer 16

glaciation caused more interconnected with proglacial lakes

Question 17

Shifts in climate regimes

Answer 17

Large changes in distribution of biomes, especially due to changes in precipitation
Ex. as cool air descends down the face of glaciers the air warms as pressure increases. The warm dry air tends to make environments near glacial margins moderate temp and dry.
General aridification and more sand dunes during glaciation
ex. NA ice sheets tended to cause jet stream splitting -> dry easterly winds
Lahontan cutthraoat trout evolved in the resulting pluvial lakes and fed on endemic forage fish tui chub - trout got really big due to big sized lakes

Question 18

Changes in sea level

Answer 18

Global changes: tremendous uptake of moisture (last glaciation 84 million cubic m)
Ocean decreased by 130 m
These drops in sea level caused formation of land bridges
ex. beringia and southeast asia and austrailia

Local changes: in high north latitude the mass of 2-3km high glaciers caused a depression of land up to 300 m in coastal areas
When icesheets retreat the rebound of land takes much longer. This results in massive inflow of marine waters that form wide expanses of shallow seas.
ex. In eastern NA influx of marine waters inundated the St. Lawrence River Valley such that large inland sea extended from the Atlantic coast to Lake ontario

Question 19

Eustatic changes

Answer 19

global changes that occur in all oceans at the same time

Question 20

Isostatic changes

Answer 20

local changes in sea level when global levels remain unchanged.

Question 21

Biogeographic consequences

Answer 21

Latitudinal Shift in Biomes- ex in NA the biomes shift northward.
Elevational shift in biomes- more rapid that latitudinal shifts, biomes move up the mountain
Range shifts- where animals live/are found change

Question 22

Biotic exchanges

Answer 22

• Great american interchange: exchange of mammals between N and SA following formation of Central american land bridge (3.5 Ma)
• Other examples btwn africa and asia, Asia to new guinea.. etc

Question 23

Great American Interchange

Answer 23

The bridge was more of a filter than a highway

more things came from the north than the south (asymmetric exchange)

Question 24

Reasons for asymmetric exchange

Answer 24

Advantage from northern forms to southern forms

1) better migrators (a lot of them came across beringia land bridge)
2) better survivors who diversified more readily
3) better competitors

Question 25

Speciation

Answer 25

Major evolutionary consequence of glaciation was the abundance of opportunities for isolation and the subsequent divergence through genetic drift and novel selection pressures

Question 26

Speciation Pump

Answer 26

the generation of diversity due to repeated fragmentation, allopatric speciation and reconnection of fauna during the glacial/interglacial cycles of the pleistocene

Question 27

Super species

Answer 27

monophyletic group of two or more allospecies (geographically seperated) or semispecies (connected geographically by a narrow hybrid zone) that have just crossed the species threshold and are presumed to be the youngest species in an avifauna. ex. vermivora, dendroica

Question 28

Pleistocene speciation pump

Answer 28

In NA more recent divergence in the boreal superspecies

Question 29

Glaciation and the origin of phylogroups (or super species)

Answer 29

Ex. All of BC’s fish fauna must have come fromrefugial populations. Some species were isolated in more than one refugium (21 species in total) giving potential for intraspecific divergence
Ex bull trout- in chehalis and columbia refuge
dolly varden and arctic char

Question 30

Glaciation and the origin of phylogroups (or super species):
Anadromous fish species

Answer 30

Some Anadromous fish species (fish that migrate from sea to rivers to spawn) can give rise to freshwater fish that do not go to sea.
Ex. pygmy smelt in lake Washington and the longfin smelt in the ocean

Question 31

What was happening to the tropics during the Pleistocene

Old view

Answer 31

Old view: Refugia hypothesis- islands of lowland rain forest persisted during glacial maxima. Developed a model of cyclic vicariance where species were seperated trough fragmentation during dry glacial periods
Ex. distribution of toucanets in the rainforest: toucanets were separated during glaical periods

Question 32

What was happening to the tropics during the Pleistocene

New view

Answer 32

New view: Refugia hypothesis was largely based on inferences from current species distribution patterns but not based on paleoecological data.
Fossil pollen data from lake cores show continuous forest cover and invasion by cold adapted species during last glacial maximum.

Question 33

Alternative Hypothesis for Refugia-like distributions

Answer 33

Amazonian ecoregions divided by large river systems are also consistent with range limits across species group.
Phylogenetic relationships of trumpeter species in SA. Distributions show that species ranges are separated by large river systems. Timing of diversification events indicates speciation prior to most recent glacial maxima

Question 34

Timeline for Trumpeter diversification

Answer 34

1) 3-2.7 Ma: western lowland Amazon is large interconnected wetland system.
2) 2.7-2.0 Ma: wetland system drained and lower amazon river was established
3) 2.0-1.0 Ma: Rio Madeira drainage established
4) 1.3-0.8 Ma: Rio Tapajos drainage established
5) 0.8-0.3 Ma: Two drainage systems on brazilian shield (rio tocatins and Xingu) established

Question 35

Extinctions

Answer 35

Massive extinctions of terrestrial mammals occurred during late pleistocene in both NA and SA. Large bodied mammals were more vulnerable.

**NA and SA suffered more than other continents - lost 76% of all genera: this is explained by both glaciation induced climate and overkill by human hunters that colonized NA and SA