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ESSHP: Section 2 > Lecture 20: Rapid Climate Change > Flashcards

Lecture 20: Rapid Climate Change Flashcards

1
Q

How is rapid climate change distinguished from normal rate climate change?

A

Rapid climate change takes place at a rate which is faster than the changes which would take place as a result of external forcings

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2
Q

Why do we need to study rapid climate change?

A

To understand their relevance and role in the early Holocene deglaciation events

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3
Q

Which milankovitch cycle has the biggest influence on earth’s climate?

A

Eccentricity - but the other cycles have had a dominance in the past

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4
Q

What is the glacial-interglacial cycle punctuated by? and what are they?

A

Sub-milankovitch cycles - millennial-scale abrupt warming or cooling events that happen on a much shorter time scale

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5
Q

What event can we see the abrupt changes that the sub-milankovitch cycles cause? When did this happen?

A

The last glacial-interglacial transition (LGIT) between 23-24kya

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6
Q

What was the LGIT named in the British literature and why?

A

Loch Lomond Stadial because the abrupt climate change was observed in lake sediments within the Loch Lomond in Scotland

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7
Q

What did the Loch Lomond come to be defined as and why?

A

Its own type sequence because it was such an abrupt change

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8
Q

what is a type sequence?

A

A sequenced event that takes place within the record

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9
Q

What is the Loch Lomond Stadial/ LGIT transition more commonly known as and why?

A

Younger Dryas Period because this name from continental NW Europe was preferred

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10
Q

How was the Loch Lomond Stadial/Younger Dryas identified within lake sediments from Loch Lomond?

A

Looking at the changes in soil colour

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11
Q

What colour will the soil be if it represents a stadial or interstadial event?

A

Interstadial: darker
Stadial: lighter

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12
Q

What characteristics of stadials and interstadials can we infer from the lake sediments?

A

intensity, duration and abruptness

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13
Q

What do the lake sediments suggest about the transition form the Younger Dryas and the Holocene?

A

It was a very abrupt change

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14
Q

What approach was taken to assess the validity and significance of the results that were gained from the lake sediment record?

A

Multi-proxy approach used to cross examine and critically assess the results

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15
Q

What other proxy techniques were used alongside the lake sediments to identify and verify the Younger Dryas period?

A

Stable oxygen isotopes and pollen analysis

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16
Q

What are the different pollen categories and what are they associated with?

A

Betula: (Woodland) Associated with warm conditions
Poaceae: (Grassland) Associated with occupying transitions between warm and cold conditions
Tundra (Cyperaceae, Artemesia) associated with much colder conditions

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17
Q

What happens to the general pollen count during cold conditions and warm conditions?

A

Cold: decreases
Warm: increases

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18
Q

Why is a multi-proxy approach commonly used for palaeoenvironmental reconstructions?

A

provides complete understandings across the whole environment
strengthens or weakens suggestions of other records
We can understand leads (causes) and lags (later impacts)

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19
Q

Where does the name Younger Dryas come from?

A

Dryas Octapelia which is a wildflower associated with alpine/tundra conditions

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20
Q

Where were the evidence of Dryas Octapelia found?

A

Fossilised within lake sediments in Scandinavia

21
Q

How many stadial events were identified from the study which discovered the Younger Dryas? What were they called and why was one studied more?

A

2: Older Dryas and Younger Dryas. Younger Dryas studied more because of its pronounced nature

22
Q

How is the Younger Dryas defined?

A

A period of relative cooing within an interglacial period to conditions experienced during the last glacial maximum

23
Q

How long is it thought that the younger dryas period was thought to have taken to come in to fruition?

A

40 years but some believe that it took just 10

24
Q

What temperature changes took place within Greenland and the British Isles during the YD?

A

Greenland: reductions of 15 degrees Celsius +

British Isles: reductions of 5 degrees Celsius +

25
Q

How long did the YD last?

A

1,100 years roughly

26
Q

Aside from the lake sediment analysis collected in Scandinavia, what other evidence is there for the YD now that it has been identified?

A

Natural archives such as stable isotopes as well as geomorphological features such as till, moraines and erratics.

27
Q

What were the pieces of evidence collected for the YD combined with?

A

Law of Superposition

28
Q

Where did evidence from the YD come from, in terms of places?

A

All over the world

29
Q

What evidence was there for the YD in Venezuela and why was it so good?

A

Sedimentary record/ series of varves that displayed spring and winter annual changes from the Cariaco Basin that terminated in an anoxic basin that was also free of biology meaning that it preserved well.

30
Q

What are varves?

A

Annually banded deposits that consist of spring and winter periods

31
Q

What was the record in Venezuela particularly sensitive to that was shown in the sedimentary record/ varve deposits?

A

Changes in the ITCZ

32
Q

What were two notable impacts of the YD period on the earth system?

A

Possible that an ice cap formed over Scotland

North Atlantic Polar Jet Stream migrated to areas consistent with changes in the ITCZ

33
Q

What is the Lake Agassiz (Northern Hemisphere) cause theory for the Younger Dryas?

A

Staged collapse of Lake Agassiz during the YD experienced four outburst events which provided a freshwater influx to the North Atlantic altering the Deep Water Current reducing the AMOC’s heat transfer between the tropics and latitudes

34
Q

What impact would the theory for the altering of the AMOC have upon the earth system?

A

Cooling within the mid latitudes and elsewhere because of global teleconnections

35
Q

What is the Southern hemisphere cause theory for the YD?

A

The YD was preceded by a meltwater pulse within the Southern Hemisphere. The pulse warmed the northern hemisphere while the southern hemisphere cooled.

36
Q

What was the name of the theory/effect of the theory for the changes in southern hemisphere that caused the YD and when did it happen?

A

Antarctic Cold Reversal (14.7-13kya - coincided with YD)

37
Q

What is the definition of the effect within the cause theory for how the southern hemisphere caused the YD? and what is it?

A

Bi-polar seesaw. This is when we have altering/fluctuating conditions between the two hemispheres

38
Q

What was also thought to have occurred at the later half of the YD and what is it?

A

Flickering - this consists of minor changes to the climate

39
Q

What was the external theory for the cause of the YD?

A

A comet impact

40
Q

What evidence was there for a comet impact causing the YD?

A

Discovery of microspherules within a confined geological period across 25 different sites across the world

41
Q

What is the proposed impact of a comet event that caused the YD on the earth system? What evidence is there?

A

Extinction of megafauna - evidence comes from the demise of Clovis Culture that disappeared suddenly form archaeological record

42
Q

Why has the comet impact theory for the cause of the YD largely been discarded?

A

Because it has not been reproducible

43
Q

What was the 8.2kyr event?

A

Another abrupt stadial climate event that took place within the Holocene?

44
Q

What was the 8.2kyr event represented as within the Greenland ice cores?

A

Cold Snap

45
Q

What suggested that the 8.2 kyr event was also caused by a similar glacial meltwater event?

A

Evidence across the North Atlantic region similar to that which existed for the YD

46
Q

What was the impact of the 8.2kyr event on the temperature of Greenland?

A

Reduction of around 6 degres Celsius with a standard deviation of 2 degrees Celsius

47
Q

What was the impact of the 8.2 kyr event on global methane concentrations?

A

15% reduction over a 150 year period with a standard deviation of 30 years

48
Q

What is the current Holocene considered?

A

A period of relative stability and warming compared to its past

ESSHP: Section 2 (14 decks)

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