Lec8: Southern Ocean and Sea Ice

Question 1

In the Northern Hemisphere, in which direction does the Coriolis force act?

Answer 1

Right to the direction of movement of the object.

Question 2

In the Northern Hemisphere, in which direction does the Coriolis force act?

Answer 2

Right to the direction of movement of the object.

Question 3

The Southern Ocean makes up the Southern region of which three oceans?

Answer 3

Indian, Pacific, Atlantic

Question 4

Why does air flow outwards from the South Pole, and how does this establish the East Wind Drift?

Answer 4

1. Cold air creates high pressure zone at S.pole
2. Flow outwards
3. Northward flowing winds are deflected left by the Coriolis force (westwards) establishing the East Wind Drift.

Question 5

Which Wind Drift contributes to the formation of two major Gyres? Name the two Gyres as well.

Answer 5

The East Wind Drift contributes to the formation of the Ross and Weddell Sea gyres.

Question 6

Is the East Wind drift circumpolar?

Answer 6

No.

Question 7

How does the Coriolis force establish the West Wind drift?

Answer 7

Southward flowing subtropical air is deflected left (eastwards) by the Coriolis force.

Question 8

Where is the West Wind drift most intense and why?

Answer 8

At the Drake Passage, where it is constricted.

Question 9

Define the Antarctic Divergence?

Answer 9

An upwelling of Circumpolar Deep water/

Question 10

How does the Circumpolar deep water contribute to the Antarctic Surface water and bottom water?

Answer 10

1. Upwelled at Antarctic divergence
2. Northward flowing portion = AAS
3. Southward flowing portion = freezes, become cold and salty
4. Being cold and dense, it mixes with ice shelf water, sinks to the bottom of the ocean and flows northward

Question 11

What are two major functions of Antarctic Bottom Water in terms of global circulation?

Answer 11

1. Major cooling

2. Supplies oxygen

Question 12

How does the Ekman spiral form?

Answer 12

1. Coriolis force deflects current left to the direction of wind
2. 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.

Question 13

How does the Ekman spiral form?

Answer 13

1. Coriolis force deflects current left to the direction of wind
2. 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.

Question 14

Why does the velocity of water decrease as it deflects more and more further down the Ekman Spiral?

Answer 14

Frictional stress.

Question 15

In the Southern Hemisphere, in which direction to Northerly winds veer, and does this lead to upwelling or downwelling?

Answer 15

Veer left (towards shore) = downwelling.

Question 16

Define Ekman transport.

Answer 16

Net movement of water due to the Ekman spiral.

Question 17

What is the significance of the vertical movement of water created by the Ekman spiral?

Answer 17

Allows nutrient and oxygen exchange between deep water and surface water.

Question 18

What two factors drive the Global ocean circulation?

Answer 18

Temperature and salinity-controlled density.

Question 19

What are the two functions of sea ice?

Answer 19

1. Insulates between water and atmosphere (preventing rapid heat loss).
2. Albedo = reflects a lot of surface radiation

Question 20

What are the stages in sea ice formation?

Answer 20

Frazil ice –> mushy Grease ice (forming pancakes) –> Pack ice –> Floes (large ice sheets)

Question 21

What is the shape of Frazil ice and why is it almost pure water?

Answer 21

1. Needle-like

2. Salt does not freeze, and is expelled as brine.

Question 22

Why does New Ice have high salt content?

Answer 22

Because liquid brine is trapped in pockets between the ice crystals.

Question 23

Why is multiyear ice stiffer and harder to crack than first year ice?

Answer 23

Because it has much less brine.

Question 24

Describe the amount of brine and air pockets compared between New Ice and Multiyear Ice.

Answer 24

Multiyear Ice = less brine and more air pockets

Question 25

How can first year and multiyear ice be distinguished by satellite sensors?

Answer 25

They have different electromagnetic properties.

Question 26

Where is Fast ice found?

Answer 26

Near shore, where sea ice attaches to land.

Question 27

Where do tide cracks form and why?

Answer 27

Forms where Fast ice attaches to shore, due to rise and fall of tides?

Question 28

Where do pressure ridges form and why?

Answer 28

Fast ice buckles under pressure.

Question 29

Compare the width and shape of leads to polynas.

Answer 29

Leads = narrow and linear passageways in ice
Polynas = large and non-linear

Question 30

Do both leads and polynas freeze in winter?

Answer 30

Leads do, but polynas remain unfrozen for ages.

Question 31

Name the two types of Polynas, giving the alternate names as well.

Answer 31

1. Sensible heat/”open water” polynas

2. Latent heat/Coastal polynas

Question 32

How do sensible heat polynas formed and why do they remain unfrozen?

Answer 32

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.

Question 33

How do latent heat polynas form and why are they considered ice-producing factories?

Answer 33

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.

Question 34

How do latent hear polynas contribute to the formation of Antarctic Bottom Water?

Answer 34

1. Frozen water/ice contains lots of brine

2. When it melts, forming cold, dense water, it sinks, contributing to Antarctic Bottom Water.