Lec8: Southern Ocean and Sea Ice Flashcards
In the Northern Hemisphere, in which direction does the Coriolis force act?
Right to the direction of movement of the object.
In the Northern Hemisphere, in which direction does the Coriolis force act?
Right to the direction of movement of the object.
The Southern Ocean makes up the Southern region of which three oceans?
Indian, Pacific, Atlantic
Why does air flow outwards from the South Pole, and how does this establish the East Wind Drift?
- Cold air creates high pressure zone at S.pole
- Flow outwards
- Northward flowing winds are deflected left by the Coriolis force (westwards) establishing the East Wind Drift.
Which Wind Drift contributes to the formation of two major Gyres? Name the two Gyres as well.
The East Wind Drift contributes to the formation of the Ross and Weddell Sea gyres.
Is the East Wind drift circumpolar?
No.
How does the Coriolis force establish the West Wind drift?
Southward flowing subtropical air is deflected left (eastwards) by the Coriolis force.
Where is the West Wind drift most intense and why?
At the Drake Passage, where it is constricted.
Define the Antarctic Divergence?
An upwelling of Circumpolar Deep water/
How does the Circumpolar deep water contribute to the Antarctic Surface water and bottom water?
- Upwelled at Antarctic divergence
- Northward flowing portion = AAS
- Southward flowing portion = freezes, become cold and salty
- Being cold and dense, it mixes with ice shelf water, sinks to the bottom of the ocean and flows northward
What are two major functions of Antarctic Bottom Water in terms of global circulation?
- Major cooling
2. Supplies oxygen
How does the Ekman spiral form?
- Coriolis force deflects current left to the direction of wind
- Surface water pushes on water below, deflecting it more left, and so on until the deeper currents are flowing in the opposite direction to the surface currents.
How does the Ekman spiral form?
- Coriolis force deflects current left to the direction of wind
- Surface water pushes on water below, deflecting it more left, and so on until the deeper currents are flowing in the opposite direction to the surface currents.
Why does the velocity of water decrease as it deflects more and more further down the Ekman Spiral?
Frictional stress.
In the Southern Hemisphere, in which direction to Northerly winds veer, and does this lead to upwelling or downwelling?
Veer left (towards shore) = downwelling.
Define Ekman transport.
Net movement of water due to the Ekman spiral.
What is the significance of the vertical movement of water created by the Ekman spiral?
Allows nutrient and oxygen exchange between deep water and surface water.
What two factors drive the Global ocean circulation?
Temperature and salinity-controlled density.
What are the two functions of sea ice?
- Insulates between water and atmosphere (preventing rapid heat loss).
- Albedo = reflects a lot of surface radiation
What are the stages in sea ice formation?
Frazil ice –> mushy Grease ice (forming pancakes) –> Pack ice –> Floes (large ice sheets)
What is the shape of Frazil ice and why is it almost pure water?
- Needle-like
2. Salt does not freeze, and is expelled as brine.
Why does New Ice have high salt content?
Because liquid brine is trapped in pockets between the ice crystals.
Why is multiyear ice stiffer and harder to crack than first year ice?
Because it has much less brine.
Describe the amount of brine and air pockets compared between New Ice and Multiyear Ice.
Multiyear Ice = less brine and more air pockets
How can first year and multiyear ice be distinguished by satellite sensors?
They have different electromagnetic properties.
Where is Fast ice found?
Near shore, where sea ice attaches to land.
Where do tide cracks form and why?
Forms where Fast ice attaches to shore, due to rise and fall of tides?
Where do pressure ridges form and why?
Fast ice buckles under pressure.
Compare the width and shape of leads to polynas.
Leads = narrow and linear passageways in ice Polynas = large and non-linear
Do both leads and polynas freeze in winter?
Leads do, but polynas remain unfrozen for ages.
Name the two types of Polynas, giving the alternate names as well.
- Sensible heat/”open water” polynas
2. Latent heat/Coastal polynas
How do sensible heat polynas formed and why do they remain unfrozen?
Upwelling of warm water (via Ekman transport) melts ice. Water would freeze (due to rapid heat loss to atmosphere), but is continuously fed by the warm water.
How do latent heat polynas form and why are they considered ice-producing factories?
Ice is blown away by winds as soon as it forms. Exposed water immediately freezes only for ice to be blown away again (positive feedback cycle), so they are continously producing ice.
How do latent hear polynas contribute to the formation of Antarctic Bottom Water?
- Frozen water/ice contains lots of brine
2. When it melts, forming cold, dense water, it sinks, contributing to Antarctic Bottom Water.
