chapter 7 Flashcards
Sea ice is
partly a meteorological and partly an oceanographic phenomenon
There are two kinds of floating ice encountered at sea:
Sea ice – formed from sea water and
• Icebergs –form when chunks of ice break off, from glaciers, ice shelves, or a larger iceberg
Sea ice is formed in
all waters of the frigid zone in both hemispheres and in parts of temperate zone in winter, particularly in the Antarctic.
Sea ice is formed in all waters of the frigid zone in both hemispheres and in parts of temperate zone in winter, particularly in the Antarctic.
• In springtime it
breaks up and spreads into more temperate waters, notably in the Antarctic and western North Atlantic
Icebergs are, in general, form in the …….zone in ………………………….
the frigid zone in the North Atlantic area and in both the frigid and temperate zone in the Antarctic.
• In the Antarctic and western North Atlantic they drift well into the temperate zone during springtime.
The physics and development of sea ice are
complicated
The freezing point of salt water is
lower than that of fresh water
The freezing point of salt water is lower than that of fresh water and is governed by its
salinity
the higher the salinity the
lower the freezing point.
Thus, in the open ocean, water with a salinity of …………………….. start freezing at about ………..
35 ppt (parts per thousand) starts freezing at about‐2 C
Thus, in the open ocean, water with a salinity of 35 ppt (parts per thousand) starts freezing at about‐2 C, while in
the Baltic, where salinity of 5 ppt is common, the water starts to freeze at 0.3C
The density of sea water
increases with salinity
The density also increases with
cooling until a maximum density forthe existing salinity is reached
The higher the salinity the
lower the temperature of maximum density.
The maximum density of water occurs at about
4C
The maximum density of water occurs at about 4 C. On the other hand, sea water with a salinity of
24.7 per cent
The maximum density of water occurs at about 4 C. On the other hand, sea water with a salinity of 24.7 per cent, has its maximum density at its freezing point of about
-1.5 C and with higher salinity the temperature of maximum density decreases further.
Formation of Sea Ice
- The cooling of surface water increases its density and it sinks, to be replaced by warmer, less dense water from below.
- The process continues until the whole column of water, from top to bottom, has attained its maximum density and all convectional descent ceases.
- Until this stage is reached, ice cannot form
formation of sea ice:
At sea it forms more readily where
the water column is stratified into layers of different density.
• In this situation convectional sinking is confined to the topmost layer.
Because, with higher salinity the temperature
of maximum density decreases further
Because, with higher salinity the temperature of maximum density decreases further, the formation of sea ice can be
a lengthy process
Because, with higher salinity the temperature of maximum density decreases further, the formation of sea ice can be a lengthy process, especially in
deep water with high salinity.
In some areas, despite very low temperatures, the winter is
not long enough for the process to be completed and sea ice does not form.
Sea ice first forms in ……………………….. where the ……………………………..
shallow water where the delay due to convectional sinking is least
The development of sea ice begins with
the formation of needle‐shaped crystals called frazil ice.
A) The development of sea ice begins with the formation of needle‐shaped crystals calledfrazil ice.
B) The frazil ice crystals then
thicken and congeal to form a greasy of soupy layer on the sea surface known as grease ice.
A) The development of sea ice begins with the formation of needle‐shaped crystals calledfrazil ice.
B) The frazil ice crystals then thicken and congeal to form a greasy of soupy layer
on the sea surface known as grease ice.
In the next stage, shuga ice develops, consisting of spongy lumps a few
centimeters across
A) The development of sea ice begins with the formation of needle‐shaped crystals calledfrazil ice.
B) The frazil ice crystals then thicken and congeal to form a greasy of soupy layer
on the sea surface known as grease ice.
C)In the next stage, shuga ice develops, consisting of spongy lumps a few
centimeters across
all the above ice are classified generally as
new ice
A) The development of sea ice begins with the formation of needle‐shaped crystals calledfrazil ice.
B) The frazil ice crystals then thicken and congeal to form a greasy of soupy layer
on the sea surface known as grease ice.
C)In the next stage, shuga ice develops, consisting of spongy lumps a few
centimeters across
D)
This is followed by pancake ice, consisting of flat pieces, roughly circular in shape, often with a rim round the edge due to rubbing against adjacent pieces.
A) The development of sea ice begins with the formation of needle‐shaped crystals calledfrazil ice.
B) The frazil ice crystals then thicken and congeal to form a greasy of soupy layer on the sea surface known as grease ice.
C)In the next stage, shuga ice develops, consisting of spongy lumps a few centimeters across
D)This is followed by pancake ice, consisting of flat pieces, roughly circular in shape, often with a rim round the edge due to rubbing against adjacent pieces.
the pancakes ……………………..
gradually join to form a more or less continuous ice sheet, called young ice, this can also be broken up by wave action.
Young ice eventually
thickens and becomes field ice or pack ice
Young ice eventually thickens and becomes field ice or pack ice, which is a
generic term for all fully developed sea ice floating on the ocean and not attached to the shore
Young ice eventually thickens and becomes field ice or pack ice, which is a generic term for all fully developed sea ice floating on the ocean and not attached to the shore; it
varies in thickness from a few inches to several feet
floes
Individual pieces of pack ice more than 20 meters across
Individual pieces of pack ice more than 20 meters across are called floes and the pack is termed
‘open’, ‘very open’, ‘close’ or ‘very close’ depending on the distance between the floes.
Very close pack leaves
little or no water visible
Pack ice originating in
Arctic or Antarctic waters
Pack ice originating in Arctic or Antarctic waters may be ………………… thick
several feet
Pack ice originating in Arctic or Antarctic waters may be several feet thick and
very uneven due to hummocking (piling up) by the waves
Icebergs
pieces of ice that formed on land and float in an ocean or lake.
Icebergs are pieces of ice that formed on land and float in an ocean or lake.
Icebergs come in
all shapes and sizes.
The term “iceberg” refers to
chunks of ice larger than 5 meters (16 feet) across.
Smaller icebergs, known as
bergy bits and growlers
Smaller icebergs, known asbergy bits and growlers, can be especially dangerous for
ships because they are harder to spot.
home to most of the icebergs on Earth
The North Atlantic and the cold waters surrounding Antarctica
Icebergs form when
chunks of ice calve, or break off, from glaciers, ice shelves, or a larger iceberg. Icebergs travel with ocean currents, sometimes smashing up against the shore or getting caught in shallow waters.
Icebergs can develop into a variety of
shapes as they break apart
Icebergs pose a danger to
ships traversing the North Atlantic and the waters around Antarctica.
Practical Ice Warnings
Provided the ship is non in a specific cold sea surface current, sea surface temperatures might indicate the vicinity of pack ice.
A sea temperature of 1C might warn of
an ice edge within about 150 miles
if the sea temperature were -0.5 C the ice edfe could be within
50 miles
Warning may be given by
ice blink caused by reflection from the ice giving a glare in the sky near the horizon, mainly white if sky is cloudy, and yellow if sky is mostly blue, it is sometimes visible at night.
practical ice warnings
In fog
white patches indicate ice at short distance
A noticeable reduction of sea and swell can warn
of pack ice to windward
Small isolated chunks of floating ice may indicate
field ice nearby.
Icing on deck occurs due to
sea spray when cold, wave‐generated spray comes in contact with exposed surfaces and the air temperature is below freezing
Ice accretion on deck may also occur due either to
the freezing of liquid rain or drizzle drops which come into contact with the vessel or snowflakes freezing onto the vessel.
Icing on deck is a serious hazard for
marine operations in high latitude regions
Many ships and lives have been lost when
ships sank, or became disabled, after the accretion of ice on decks and superstructures.
Dangers of icing on Deck
Large amounts of ice can
raise the center of mass on a ship enough to result in a catastrophic loss of stability.
………………………………………………….. an occur as a result of the loss of stability and extra weight from the ice burden.
Capsizing, extreme rolling and/or pitching, and topside flooding
Capsizing, extreme rolling and/or pitching, and topside flooding can occur as a result of the loss of stability and extra weight from the ice burden.
The problem is particularly dangerous for
smaller ships, such as fishing vessels
Capsizing, extreme rolling and/or pitching, and topside flooding can occur as a result of the loss of stability and extra weight from the ice burden.
The problem is particularly dangerous for smaller ships, such as fishing vessels, because
they are more likely to be exposed to sea spray and a relatively smaller amount of ice is required for destabilization.
