Topic 10Ice and Fog

GEOL 2503Introduction to Oceanography

Ice

• Ice is fresh water, pure H2O • Dissolved materials are left behind in the

surface water• Remaining surface water has increased

salinity (same amount of salt, less liquid water)

Sea Ice

Frozen ocean surface water

Photos from the International Ice Patrol photo gallery: http://www.uscg.mil/lantarea/iip/Photo_Gallery/Category.shtml

Land Ice

• Earth's ice cover formed on land as the result, principally, of the freezing of precipitation

• Takes water from one reservoir (ocean) and moves it to another (land)

• Changes the volume of water in oceans (and sea level)

Ice Sheets

• Regional, extensive covering of land ice• Antarctic—largest• Greenland—second largest• Sometimes referred to simply as glaciers,

but there are also small glaciers in mountains and elsewhere that are not ice sheets

More Ice Terms

• Fast Ice—sea ice anchored to land mass, doesn’t move

• Ice Floe—sea ice not anchored, moves with currents

• Iceberg—broken off chunks of land ice

Icebergs

• Ice is about 10% less dense that liquid water

• So only about 10% floats above water• “tip of the iceberg”

Icebergs off Greenland

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Iceberg photos from IIP:

1. Coast Guard plane

2. Tabular iceberg

3. World’s tallest iceberg, 550 feet

Notice the latitude at which the Titanic sank. Since then, the sea surface has warmed enough that today there are no icebergs south of about 45 degrees north latitude

Life of an Iceberg

This is the basic drift of an average iceberg during its 2-3 year life cycle.

The numbers correspond to the next few slides showing the different stages of the iceberg's life in more detail.

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4

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Birth (very large iceberg)

Photo of glaciers on Greenland's West Coast which produces most of the icebergs that drift down into the north Atlantic shipping lanes.

Childhood (large to very large icebergs)This photo shows winter off of Baffin Island, and the many very large icebergs that spend the early part of their "lives" there.

Teen (medium icebergs)

Here is the rugged coastline of Labrador, where large icebergs often ground themselves or break up into smaller pieces as they continue traveling south.

Young Adult (medium rolling or breaking-up icebergs)

This picture shows the St. John's, Newfoundland area, where medium-sized icebergs continue to break up and roll through shipping lanes and past oil rigs.

Old Age (small icebergs)When the iceberg reaches this stage it is often small in size (also called a growler) from years of melting and breaking up. Once icebergs reach old age, they quickly

Water Cycle of an Iceberg(see next slide)

• The life cycle of the iceberg is also a key part of nature's water cycle. • First, water in the ocean (including water from the small melted

icebergs) evaporates and forms clouds. • Some of those clouds are then carried by the wind over the country of

Greenland where the cold air causes them to condense. • This condensation causes the clouds to release the water as

precipitation in the form of snow. • This snow fall builds for thousands of years, and then compresses to

form glaciers. • Due to their immense weight the glaciers are then forced down to the

ocean by gravity. • As they reach the ocean pieces of the glacier break off and fall into the

ocean, creating icebergs. • The iceberg goes through its life cycle, travels through the ocean,

grows smaller over time and then once again melts, starting the water cycle all over again.

The water cycle of an iceberg (see previous slide)

Iceberg Shapes

• 1. Tabular (Flat)• 2. Wedge• 3. Dome• 4. Blocky• 5. Dry-docked (Connected under water)• 6. Pinnacled (Pointed) • 7. Non-tabular (Anything else)

1.  Tabular  (Flat)

2.  Wedge

3.  Dome

3.  Blocky

5.  Dry-docked  (Connected under water)

6.  Pinnacled  (Pointed)

7.  Non-tabular  (Anything else)

Fog• Cloud at ground level• Form when air can’t hold all the water

vapor (cool air can’t hold as much as warm)

• Fog/clouds are liquid water—droplets• Three types

– Advective– Radiative– Sea Smoke

Advective Fog

• Warm air, saturated with water vapor• Moves over colder water• Blanket of fog forms at surface of water• Tends to persist• Grand Banks• San Francisco

Radiative Fog

• Warm days, cold nights• Earth surface cools at night• So does air above surface• Moisture in air condenses at night• Forms low-lying, thick fog• Dissipates as air warms, water evaporates• Also called “radiation fog”

Sea Smoke

• Dry, cold air• Moves over warmer water• Water warms air above it• Air picks up moisture from water• Warmed air rises rapidly• Air cools, water vapor condenses• Forms ribbons of fog

How sea smoke forms

Ice Fog

• forms when the air temperature is well below freezing

• composed entirely of tiny ice crystals that are suspended in the air

• will only be witnessed in cold Arctic / Polar air

• Generally the temperature will be 14 F or colder in order for ice fog to occur.

Ice fog

Freezing Fog• Occurs when the water droplets that the fog is

composed of are "supercooled“• Supercooled water droplets remain in the liquid

state until they come into contact with a surface upon which they can freeze

• Any object the freezing fog comes into contact with will become coated with ice.

• The same thing happens with freezing rain or drizzle.

Freezing fog