Oceans and Ice Ages

Question 1

‘Thermohaline circulation’ (THC)…

Answer 1

is the name given to the global ocean circulation

system

Question 2

Why is ‘Thermohaline circulation’ (THC) important…

Answer 2

THC is important because it acts to transfer heat around the Earth

Question 3

How does THC circulation work?

• The circulation is driven by differences in:

Answer 3

– sea water temperature (thermo)
– sea water salinity (haline)

• Cold water = high density
• Saline water = high density
• Cold / Saline water sinks forming ‘DEEP WATER’
• Surface waters rush in to replace the sinking column of
deep water

Question 4

Mechanisms for North Atlantic Deep Water (NADW) formation

Answer 4

(1) Warm water travels north and cools becoming more dense
(2) Evaporation losses make the sea more saline
(3) In the far north as water freezes to make sea ice the salt is left in the water below the ice – this saline water sinks because its density is high

Question 5

Disruption to NADW formation can have a
major impact on the THC

THC can be disrupted if the temperature and / or
salinity of sea water in the zone of deep water formation is altered.

Answer 5

1. Iceberg calving
2. Melt water discharge
3. Warming of surface waters

Question 6

Freshwater outburst from glacial Lake Agassiz

Answer 6

• Lateglacial stadial was preceded by a massive outflow from Lake Agassiz
• 9,500 cubic kilometres of freshwater poured into the most sensitive area for NADW formation
• The freshwater is less dense than sea water and sat on the surface of the ocean preventing ‘deep water’ formation around Iceland

Question 7

Proposed causes of the Lateglacial Stadial

Answer 7

1. Drainage of cold meltwater from glacial Lake Agassiz
2. Collapse of Barents Sea Ice Sheet
3. Changes in insolation caused by volcanic ash
4. Changes in the Jet Stream
5. Changes in solar radiation
6. Strong winds caused by increased high pressure over
   Greenland
7. A surge of the Canadian ice sheet
8. Fluctuations in atmospheric CO2
9. Meteorite impact (air burst explosion over N. American
   ice sheet)

Question 8

• Lateglacial - 9,300 km3 discharge causes full glacial/ interglacial scale climate oscillation
• 8,200 BP – 163,000 km3 discharge is followed by climate cooling only 1/3 that of Lateglacial Stadial
Why?

Answer 8

1. THC has a weak glacial circulation and strong interglacial circulation
   Lateglacial freshwater outburst occurred when THC was still fairly weak
   8,200 event occurred when THC circulation was in strong interglacial mode
2. The Lateglacial outburst was routed to the most sensitive part of the North Atlantic
   The 8200 outburst occurred much further north in Hudson Bay in an area less critical to NADW formation