L6 - Millennial Scale Climate Change (Mechanisms)

Question 1

What 3 things does any theory explaining climate system oscillation need to explain?

Answer 1

1. Initiation
2. Transmission (the bipolar seesaw)
3. Glacial magnification

Question 2

Ocean circulation is sensitive to what?

Answer 2

Small changes meaning it can shift abruptly from one state to another

Question 3

What does it mean if the system is close to a threshold?

Answer 3

A small change in forcing could lead to a large change in circulation

Question 4

What happens under glacial boundary conditions?

Answer 4

There a small variations in freshwater causing switching between deep water formation in the Nordic Seas vs. South of Iceland

Question 5

What are the 2 types of hypotheses for explaining abrupt climate change?

Answer 5

1. Internally generated oscillations

2. External forcing

Question 6

What are the 4 scenarios for Internally generated oscillations and which helps explain H and D-O events?

Answer 6

1. Binge Purge of the LIS
2. Broecker’s Salt Oscillator (D-O-Event)
3. Nordic Sea Ice Mechanisms
4. A Tropical Pacific Mechanism

Question 7

What are the 2 scenarios for external forcing?

Answer 7

1. Periodic External Forcing (e.g. 11 year solar cycles)

2. Stochastic Response (Adding Noise!)

Question 8

What are the 7 steps in the Binge Purge of the LIS?

Answer 8

1. Much of the LIS sat on hard crystalline bed
2. In the Hudson Bay/Strait it was soft carbonates and mudstones which easily erode unless frozen
3. Binge Phase: stable, frozen bed allows an ice dome to form
4. Ice acts as an insulator + geothermal heating = melting at the base
5. Purge Phase: ice sheet collapse and iceberg calving
6. Icebergs disrupt N.Atlantic ocean circulation
7. Removal of ice increases heat removal and the bed refreezes

Question 9

What is Broecker’s Salt Oscillator?

Answer 9

In the strong mode it is warm and fresh until it becomes too warm and fresh and it switches off. in the off mode salinity builds up until this is too much and it switches back on. and the cycle repeats.

Question 10

What impact do tropical SST have?

Answer 10

They control atmospheric heat transport patterns

Question 11

What is ENSO and its frequency?

Answer 11

El Niño Southern Osscilaiton (~2-7 Years)

Question 12

What do Normal - La Niña conditions do?

Answer 12

Aid growth of the LIS

Question 13

What do El Niño conditions do?

Answer 13

Aid ablation of the LIS

Question 14

What are the Nordic Sea Mechanisms?

Answer 14

Sea ice cover across the North Atlantic can cause large amplitude cooling across Greenland. Sea ice cover and freshwater cap in the stadial prevents heat loss. eventually this become unstable and leads to catastrophic collapse of ice shelves which relearns heat and causes destratification and a return to the interstadial

Question 15

Give 2 points that show the relationship between D-O events and H-events

Answer 15

1. H events are all followed by particularly warm D-O events
2. H events always occur during cold stadials not warm interstadials