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ESSHP: Section 2 > Lecture 17: Ice Age Earth II Northern Hemisphere > Flashcards

Lecture 17: Ice Age Earth II Northern Hemisphere Flashcards

1
Q

What were the two main ice sheets that comprised the surface of North America during the Ice Ages?

A

Laurentide Ice Sheet and Cordilleran Ice Sheet

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2
Q

What were the two ice sheets in North America divided by?

A

Rocky Mountains

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3
Q

How thick was the Laurentide ice sheet and what area did it cover?

A

3km thick, 33 million km^2

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4
Q

What happened to the Cordilleran and Laurentide Ice Sheets during the last glacial maximum?

A

They merged together

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5
Q

What was the mass of the combined Laurentide and cordilleran ice sheets equivalent to?

A

1.5x Antarctic Ice Sheet today

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6
Q

What are the 2 reasons for why there is a strong focus on quaternary climate and environmental change, particularly in reference to ice ages in the northern hemisphere?

A
  1. Because there is a historical bias that stems from the location of certain prestigious universities
  2. Evidence that the North Atlantic region was responsible for driving global changes through teleconnections
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7
Q

What is the North Atlantic Oscillation?

A

Differential pressure gradient between the subpolar and subtropical points in the North Atlantic?

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8
Q

What is the name of the subtropical and subpolar points in the Atlantic that form components of the NAO?

A

Subpolar: Icelandic
Subtropical: Azores

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9
Q

What does the NAO influence?

A

The location of the North Atlantic Jet Stream and northern westerlies, and it also modulates the patterns of zonal and meridional heat and moisture across the region which then affects temperature and precipitation

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10
Q

What is the pressure gradient like in a positive and negative phase of the NAO?

A

Positive: Strong Azores high pressure and Strong Icelandic low pressure
Negative: Weak azores high and weak Icelandic low

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11
Q

What happens to one thing that the NAO influences in a positive phase?

A

Jet stream is forced north

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12
Q

What happens to one thing that the NAO influences in a negative phase?

A

enhancement of the peak-trough in jet stream (it gets wavier)

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13
Q

What does the location of the jet stream influence?

A

Distribution of weather events

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14
Q

What is the Atlantic Meridional Oceanic Circulation (AMOC)?

A

Northward flow of warm, salty surface water (including the gulf stream) from the tropics to the North Atlantic. There is also a southward deep-water flow of colder water forming the thermohaline circulation

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15
Q

How does the AMOC affect the climate of NW Europe?

A

The heat that it carries is lost to the atmosphere which warms NW Europe to a degree that prevents it form having a climate like Canada

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16
Q

What general impact does the AMOC have on climate?

A

Affects sea surface temperatures, arctic sea ice build up, moisture supply

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17
Q

What can more moisture supply affect?

A

Precipitation - but if it is being transported to the colder latitudes then it increases the likelihood of snowfall

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18
Q

How can the melting of sea ice affect the AMOC?

A

It affects the salinity of the oceans which then alters the functioning of the thermohaline circulation that forms part of the AMOC

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19
Q

What was the North Atlantic characterised by in the Quaternary period?

A

Glacial and interglacial cycles punctuated by stadials and interstadials

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20
Q

What are Dansgaard-Oeschger events?

A

Interstadial periods

21
Q

What are interstadial/Dansgaard-Oescher events when are they more common?

A

Rapid and abrupt warm periods that are less common during interglacial periods

22
Q

How many D-O events were there during the last glacial period?

A

25

23
Q

What are D-O events characterised by in the Northern Hemisphere? (statistics)

A

Rapid Warming of ~5-8 degrees Celsius over 40 years in some places (Greenland) then followed by slower cooling

24
Q

What are D-O events characterised by in the Southern Hemisphere?

A

Slow warming with smaller fluctuations.

25
Q

What is the debated periodicity for which D-O events take place?

A

1470 years

26
Q

What are Heinrich events?

A

Stadial events

27
Q

What do Heinrich events precede?

A

D-O events

28
Q

How many Heinrich events have currently been identified within the quaternary?

A

6 - many others identified

29
Q

How do we know about Heinrich events?

A

As a glacier moves over land it scrapes up terrestrial sediments, then once it breaks off an ice sheet and enters the ocean, eventually these sediments are deposited in the ocean floor. Today we can look at the marine cores and identify this ‘ice rafted debris’ that contain information which indicates these Heinrich events

30
Q

What uncertainty is there about the mechanism of Heinrich and D-O events?

A

Their drivers - internally (NAO, freshwater pulses, thermohaline circulation) or externally (Milankovitch and solar activity). MOREOVER, if external then there is uncertainty around periodicity link with Milankovitch and the ice events

31
Q

What happened to the landscape of North America after the Laurentide and Cordilleran ice sheets melted?

A

Massive proglacial lakes were formed.

32
Q

How do proglacial lakes form?

A

When the glacier at its maximum extent deposits sediment, it forms a dam and then as it retreats away from here the melting ice forms a lake in between the glacier and the sediment it deposited previously

33
Q

How long did it take for the cordilleran ice sheet to melt?

A

4000 years

34
Q

What three proglacial lakes formed after the cordilleran ice sheet melted? M, C, A

A

Missoula and Columbia and Agassiz

35
Q

What happened as a result of the unstable banks that formed the banks of the lakes that formed after the cordilleran ice sheet melted?

A

Missoula floods

36
Q

What formed as a result of the Missoula floods?

A

Channelled Scrublands - essentially a shallower Grand Canyon

37
Q

What area did Lake Agassiz cover?

A

Manitoba, Ontario and part of Quebec

38
Q

What is the modern remnant of Lake Agassiz?

A

Lake Winnipeg

39
Q

What happened to Lake Agassiz and what impact did it have? (sea level and circulation)

A

It experienced a massive flooding event that flowed in to the North Atlantic - this resulted in global sea level rise of 20-40cm and the input of freshwater altered the thermohaline circulation

40
Q

When are homosapiens thought to have reached North America and was this early or late? Put in to context

A

15kya - very late. In Europe 40kya and Africa 200kya

41
Q

What led to homosapiens occurring in North America?

A

They migrated down from Russia through Alaska

42
Q

What prevented the homosapiens from reaching the mainland of North America initially?

A

The coast-to-coast barrier that was created by the two ice sheets that existed

43
Q

When is it thought that homosapiens started to enter the middle of the North America?

A

12-13kya

44
Q

When was the first human archaeology found in North America dated do using radiocarbon dating? What debate has this sparked and how is it partially resolved?

A

14.5-18kya. When in fact did homosapiens enter the North Atlantic? It is pinned upon inaccurate estimations

45
Q

What is an alternative idea for how homosapiens reached North America?

A

Came down the Western coast

46
Q

What else was found in the archaeological record in North America? and when was it dated to?

A

Megafauna - dated to 11kya (debated)

47
Q

What is thought to be the reason for the extinction of megafauna?

A

advent of climate change or humans or both

48
Q

Was the northern hemisphere thought to be a cause or recipient of global climate changes?

A

Not sure (debate) meaning that there needs to be further investigation.

ESSHP: Section 2 (14 decks)

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