Air and Sea

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Air and Sea Interaction
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Oceans in Motion

• The ocean is constantly in motion
• Driven by
• Winds
• Currents
• Coriolis Effect

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• WINDS ARE NAMED FROM WHICH THEY BLOW
• CURRENTS ARE NAMED BY THE DIRECTION THEY FLOW

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Gulf Stream travels from the Gulf of Mexico
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What causes ocean currents?

• Winds produce a stress on the ocean and cause it
  to move
• Wind-Driven Circulation
• Density differences created by the exchange of
  heat and moisture with the atmosphere cause
  movement
• Thermohaline Circulation

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How does the Ocean Circulate?

• Similar to a two story building
• There is an upstairs and downstairs
• What goes on in each floor is separated by the
  floor or ceiling
• Connections between the two floors occurs only at
  limited locations
• Where elevators or stairways are found

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Mixing

• In the oceans two stories, there is the surface
  and deep ocean.
• The floor that separates them is called the
  pycnocline
• Effectively restricts direct mixing across this
  level
• Connections between the two parts of the ocean
  are only in limited regions

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Cyclones and Hurricanes

• Doldrums convergence of trade winds fuel
  tropical cyclones and hurricanes

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OCEAN CIRCULATION

• Ocean water circulates in currents
• Surface currents are caused by wind
• 10 of water movement
• The other 90 is driven by gravity
• dense water sinks, less dense rises

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The Great Ocean Conveyor Belt
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January 10, 1992.
When several containers of children's bathtub
toys spilled over a ship's side and were released
into the Pacific Ocean, who would've thought a
concerted research project to study the ocean's
currents would be the result?
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• In January 1992, a container ship near the
  International Date Line, headed to Tacoma,
  Washington from Hong Kong, lost 12 containers
  during severe storm conditions.
• One of these containers held a shipment of 29,000
  bathtub toys.
• Ten months later, the first of these plastic toys
  began to wash up onto the coast of Alaska.
• Driven by the wind and ocean currents, these toys
  continue to wash ashore during the next several
  years and some even drifted into the Atlantic
  Ocean.

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60,000 Nike shoes wash ashore from ship spill
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Scientists use these spills to help study ocean
circulation

• This could help with oil spills and predicting in
  which direction the oil will travel
• Learn about pathway of currents and how they are
  changing and what affects them.

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Winds effect water movement
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How do the winds make the ocean move?
A Bad Break in Pool
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A Bad Break in Pool
Not the worst one ever, just a bad one

• cue hits at bad angle
• cue moving too slowly
• billiard balls poorly racked up

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A Bad Break in the Ocean

• Air molecules hit water molecules at bad angle,
  AND
• H2Os irregularly spaced
• hydrogen bonded together
• imagine golf ball hitting billiard balls that
  are poorly racked

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Transfer of Kinetic Energy from Air to Ocean

• BILLIONS of air molecules hit the ocean every
  second
• The upper 100 m of the ocean moves in response
  to winds
• BUT
• the water does not move in EXACTLY the same
  direction as wind

O2
N2
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• Wind bombards the surface ocean
• Water starts to move
• Coriolis deflection alters its path

Ekman Transport
Sverdrup et al., Introduction to the Worlds
Oceans, 8th edition, McGraw Hill, Fig. 9.1
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• Remember that the Earth is rotating clockwise
  to the east.
• Objects traveling in Northern hemisphere are
  deflected to right (clockwise)
• Southern hemisphere are deflected to left
  (counterclockwise)

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The Coriolis Effect

• The Earths rotation affects linear movement it
  is deflected, the path is not linear, rather it
  is curvilinear
• 2. The effect is too subtle to notice over short
  distances, but things which travel over long
  distances such as airplanes, winds, and water
  currents display the Coriolis effect.

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Ekman Spiral

• surface layer (1) drags on
• the water underneath (2).

1
2
3

• layer 2 starts to move.
• It moves more slowly
• than layer 1 due to
• friction.
• (smaller yellow arrow)

• Coriolis deflection
• alters path of layer 2.

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Ekman Spiral

• layer 2 drags on the water underneath
• (layer 3).

1
2
3

• layer 3 moves more slowly

• Coriolis deflection alters path of layer 3.

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Ekman Spiral

• The result?
• A spiral pattern.

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2
3

• AVERAGE MOTION
• of the upper 100m
• of the ocean is 90
• to the wind.

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Building the currents STEP 1 Ekman Transport

• Winds drive E-W currents

• Zones of convergence
• and divergence

• Continents get in the way
• EXCEPT around Antarctica
• (stormiest ocean on Earth)

• Pattern of circulating
• GYRES.

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Geostrophic Flow
Sargasso Sea - a mound of water in the Atlantic
Ocean
Coriolis deflection is piling up water. Gravity
is pulling it down.
The pile is ALWAYS THERE. These forces must be
EQUAL.
Sverdrup et al., Introduction to the Worlds
Oceans, 8th edition, McGraw Hill, Fig. 9.4
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Sargasso Sea Sea of Weeds
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Sargasso Sea Home to Many
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Gyres

• Circuit of mid-latitude currents around the
  perimeter of an ocean basin.
• Example the Gulf Stream, the North Atlantic
  Current, the Canary Current, the North
  Equatorial Current make up the North Atlantic
  Gyre

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Five major gyres and the Antarctic circumpolar
current
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Gyre Formation
CLOCKWISE
Warm Cool
COUNTER CLOCKWISE
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North Atlantic Gyre

• Notice how the winds are helping the currents.
• This also shows the effects of the Eikman spiral

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What happens when you push in on a plastic
container of water?
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The container moves first, and water moves a
fraction of a second later.
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Water sloshes up again the left-hand side,
creating a pile
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As Earth rotates the continents smack into the
oceans
The Americas hit the Atlantic Ocean
Asia, Australia hit the Pacific Ocean
Sverdrup et al., Introduction to the Worlds
Oceans, 8th edition, McGraw Hill, Fig. xxx
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A West to East Cross Section of the mound of water
Continents crash into the mound of water. The
mound is asymmetrical. This leads to Western
Intensification water piles up on the coast
West
East
North America
1m
Only 1m high, but thats enough to create
BIG differences in the currents.
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Western Intensification
A West to East Cross Section of the mound of water
East
West
North America
Gravity is trying to pull this down and out to
flatten the ocean.
The flow is constricted on the WEST side and
spread out on the EAST
Think about constricting flow out of a garden
hose by covering half the opening with your
thumb. The constricted flow moves FASTER.
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Western Intensification
East
West
North America
Think about constricting flow out of a garden
hose by covering half the opening with your
thumb. The constricted flow moves FASTER. WHY?
SAME AMOUNT of water forced to move through
smaller opening
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Western vs. Eastern Currents
Western Currents
Eastern Currents

• Gulf Stream, Kuroshio,
• East Australia Currents

• California, Canary, Peru
• Currents

• warm water moving from
• equator to pole

• cold water moving from
• pole to equator

• narrow lt 100 km wide

• wide 1000 km wide

• deep down to 2 km

• shallow lt 500 m

• fast 100s of km/day

• slow 10s of km/day

• sharp boundaries defined by
• water temperature

• diffuse boundaries

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Coupled Surface and Deep water Circulation
Sverdrup et al., Introduction to the Worlds
Oceans, 8th edition, McGraw Hill, Fig. 9.14
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Back to Upwelling Downwelling
Upwelling brings NUTRIENTS (from DECAYED
organic matter) back up to the surface.
Sverdrup et al., Introduction to the Worlds
Oceans, 8th edition, McGraw Hill, Fig. 9.3
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ITCZ Inter-Tropical Convergence Zone

• Area where trade winds converge
• Meteorlogical equator Thermal equator
• Moves north south of the Earths equator

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Major Zones of Convergence and Divergence
Sverdrup et al., Introduction to the Worlds
Oceans, 8th edition, McGraw Hill, Fig. 9.11