Deglaciation and Postglacial

Question 1

What period of time was the last deglaciation?

Answer 1

The LR04 ocean core stack
present day tp 5.3 Ma BP

Question 2

What are climate archives?

Answer 2

• Sediment cores
• Ice cores
  > annually resolved layers (although the layers get thinner with depth
  > Gives very precise chronology (i.e. age) - constrained by volcanic eruptions and ice flow models

Question 3

What is the global ocean thermohaline circulation?

Answer 3

Network of ocean currents driven by contrasting temperature and salinity ( ie density)
- Helps redistribute energy around the globe

Question 4

What are the general principles of the thermohaline circulation?

Answer 4

• Cold/saline water is dense - sinks - flow at depth
• Warm/ fresh water is less dense - flows close to the surface

Question 5

What is the thermohaline circulation driven by?

Answer 5

Cold water sinking in the polar regions

Question 6

What is the main focus of the THC?

Answer 6

Atlantic meridional overturning circulation (AMOC)

Question 7

What happened to the AMOC during the last glacial?

Answer 7

Was suppressed by presence of ice sheets and supply of melt into N Atlantic - Gluf stream cannot transport heat as far North

Question 8

What caused rapid warming into the Bølling–Allerød?

Answer 8

• AMOC strengthened abruptly, causing warm surface waters to be transported further northwards
• But at a time when the melting of N Hemisphere ice sheets were significant (which tends to weaken the AMOC)

Question 9

What went on during the Bolling-Allerod period?

Answer 9

• A sudden reduction in meltwater input to N. Atlantic
• reduced iceberg production in the Barents Sea
• Interactions with Southern Ocean/Antarctica?
• Freshwater input into the Gulf of Mexico

Question 10

Facts about the Svalbard-Barents Sea Ice Sheet

Answer 10

• Mostly grounded below sea level
• Which makes it less stable than ice grounded above sea
• Will have deglaciated more rapidly than other ice sheets, through iceberg calving
• Icebergs melt in the N Atlantic, supressing the AMOC

Question 11

What happened during the transition from BA to YD?

Answer 11

Rapid cooling
- Warmer Bolling-Allerod was followed by rapid cooling into the Younger Dryas
- Caused by another change to the THC

Question 12

What did the catastrophic drainage of N American ice cause?

Answer 12

Glacial Lake Agassiz
- Freshwater input to the ocean
- Old theory suggests that between BA and YD, the route switched from southern to eastern
- Geochronological evidence for the northern route into Arctic Ocean

Question 13

What was the impact on the AMOC

Answer 13

• Freshwater covered surface of N. Atlantic, preventing the formation of NADW
• Then means the overturning happens further south
• Warmer surface waters from lower latitudes do not reach as far north
• therefore climate cooling

Question 14

How did the Holocene begin?

Answer 14

• YD ended with abrupt warming 11.7 ka before present
• Strengthening of the AMOC - overturning circulation happens further north

Question 15

What does a post-glacial landscape look like?

Answer 15

• Sediment and scoured bedrock
• No vegetation/ little obvious life

Question 16

What was Britain like during these periods?

Answer 16

• Proxy evidence of environmental change is British sediments
• Sediments from peat bogs and lakes are best

Question 17

What was Britain like during the Bolling-Allerod interstadial?

Answer 17

Hawes Water record indicated significant environmental change

Question 18

What was Britain like during the Younger Dryas?

Answer 18

Glaciers
- By the end of the BA interstadial, most/all of the glaciers in Britain had disappeared
- But the Younger Dryas triggered cooling sufficient to allow glaciers to return
- Very clear glacial geomorphological evidence

Question 19

Britain during the Younger Dryas: Climate

Answer 19

BA to YD saw British temperatures drop by 4C

Question 20

Britain at the start of the Holocene: Temperatures

Answer 20

Rapid warming of around 3-4C

Question 21

British environment at the start of the Holocene

Answer 21

• Climate warms
• Glaciers disappear
• Landscape could be recolonised by a larger wider variety of vegetation compared to the tundra grassland of the YD
• Vegetation succession

Question 22

What was the Mid-late Holocene like?

Answer 22

5-6,000 years ago, mixed deciduous woodland was established as the dominant vegetation type
- Britain should be covered in this vegetation…

Question 23

The Anthropocene?

Answer 23

• From the mid-late Holocene, the British landscape has been dominated by humans
• Evidence of tree clearance and beginnings of agriculture
• Evidence of grass begins to dominate in the pollen record
• A new epoch?
• Currently being considered for official epoch status, alongside the Pleistocene
  (2.588Ma-11.7ka BP) and the Holocene (11.7ka to present)
• Debate as to when it should start (mid-Holocene agricultural boom, industrial
  revolution, nuclear age?)