CH07 Sea Ice

Question 1

At what temperature does water freeze?

Answer 1

FW 0°

SW

Question 2

What are the common types of ice?

Answer 2

Floating ice - formed by sea surface freezing.
Icebergs - ice which has broken away from a glacier.
River ice - surface ice which forms in harbours/estuaries.

Question 3

What is the most dangerous ice formation for shipping?

Answer 3

Old/Multi-Year Ice (3-6m thick).
This ice has survived at least one summer melt in the Arctic.
Usually found in the Arctic but may drift south.
Strong blue colour.
Flats higher in the water due to being salt free.
As hard as concrete.
Should be give a wide berth by all shipping.

Question 4

What proportion of sea ice floats above water?

Answer 4

1/7 of the total thickness.

Question 5

What are the months of greatest extent of drift ice?

Answer 5

Arctic - March or April.

Antarctic - September or October.

Question 6

What are the months of least extent of drift ice?

Answer 6

Arctic - August or September.

Antarctic - February or March.

Question 7

What regions do icebergs of the Arctic mostly flow?

Answer 7

E and W coast of Greenland.

E seaboard of Canada.

Question 8

What effects does ice have on how we navigate?

Answer 8

Restricts and controls movements.
Affects DRs by forcing frequent course/speed changes.
Alters appearance of landmarks.
Affects propagation of radio waves.
Reflects radar signal differently.
Alters refraction and obscures horizon.

Question 9

What is the best way to detect icebergs?

Answer 9

Visual sighting is the only sure way.
Icebergs can be difficult to distinguish in certain situ.
The first sight may be the sea breaking on its base.
Complete reliance on radar can be dangerous.

Question 10

What are the likely signs an iceberg is in the vicinity?

Answer 10

The absence of sea in a fresh breeze indicates the presence of ice to windward.
Thunderous roar or sound of distant discharge of guns may indicate calving.
Growlers or smaller pieces of brash ice.
The sound of breakers may be heard and should be listened for.
Sea temp may indicate cold ice-bearing waters.

Question 11

What are the likely signs of drift ice?

Answer 11

Ice blink - luminous yellow haze on the horizon on clear days (whitish glare on clouds on overcast days).
Abrupt smoothing of the sea - this indicates drift ice to windward.
Sea surface temps - used to assume proximity (150nm) to ice.