Transcript Ocean Currents

Ocean Currents
• Ocean Current
– Large scale horizontal flow of ocean water
that is persistent and driven by atmospheric
circulation.
Types of Ocean Currents:
1. Surface Currents--Surface Circulation
•
These waters make up about 10% of all the water in the
ocean.
•
These waters are the upper 400 meters of the ocean.
2. Deep Water Currents--Thermohaline Circulation
•
These waters make up the other 90% of the ocean
Deep waters are "formed" where the air temperatures are
cold and where the salinity of the surface waters are
relatively high. The combinations of salinity and cold
temperatures make the water denser and cause it to sink to the
bottom, causing a system of slow, deep water currents. In order
for sea level to remain constant, if water sinks in one area, it
must rise somewhere else. These areas where deep water
rises to the surface are called areas of upwelling.
• Ocean waters are constantly on the move.
How they move influences climate and living
conditions for plants and animals, even on
land.
• Currents flow in patterns affected by:
wind
the water's salinity and heat content
bottom topography
earth's rotation
Lets Look Specifically at Some Factors
That Affect Ocean Currents:
1. Solar Heating
2. Winds
3. Gravity
4. Coriolis
1. Solar Heating
Solar heating causes water to expand.
Near the equator the water is about 8
centimeters higher than in middle
latitudes. This cause a very slight slope
and water wants to flow down the
slope.
Differential Solar Heating
2. Wind
• Winds blowing on the surface of the
ocean push the water, creating
currents. Friction occurs between the
wind and the water's surface.
• A wind blowing across the ocean will
cause the surface waters to flow at
about 2% of the wind speed.
• Water will pile up in the direction the
wind is blowing, and currents will
travels until they strike an object
(continent).
3. Gravity
Gravity will tend to pull the water down
the "hill" or pile water against the
pressure gradient.
4. Coriolis Effect
• This effect is caused by the
rotation of the Earth.
• Winds blow at an angle to
the equator.
• Winds in the northern
hemisphere blow to the
right and winds in the
southern hemisphere blow
to the left.
Trade Winds
• Ground-level
winds that flow
toward the equator
and are deflected
by the rotation of
the Earth. This
deflection is the
Coriolis Effect.
Prevailing Westerlies
• Winds that occur between
30 and 60 degrees
latitude.
• The air moves towards
the poles and appears to
curve to the east. Winds
originate in the west.
• These winds are
responsible for many of
the weather movements
across the US and
Canada
Coriolis continued…
Large mounds of water
and the flow around
them are called
Gyres. They produce
large circular currents
in all the ocean
basins.
Hadley cell
H
Coriolis effect and
continents affect
surface current
directions
Equator
L
L
L
H
Air moving from polar
areas to tropics (wind)
sets surface ocean
water in motion
Hadley cell
• The North Atlantic
Gyre is separated
into four distinct
currents: The North
Equatorial Current,
the Gulf Stream, the
North Atlantic
Current, and the
Canary Current.
Clockwise in Northern Hemisphere
Counter-clockwise in Southern Hemisphere
• Near surface warm currents are drawn in red.
• Blue depicts the deep cold currents.
• This system is continuously moving water from the surface
to deep within the oceans and back to the top of the ocean.
• One complete circuit of this flow of sea water is estimated
to take about 1,000 years.
http://www.youtube.com/watch?v=QsEbP5z
arCQ&NR=1
Ocean "conveyor belt”
• surface waters sink, enter deep water circulation, then resurface
after slowly flowing through the deep ocean.
• Connects all the world’s oceans!
Great Ocean Conveyor Belt
• Has enormous effects on:
– World climate (heat transfer)
– Fishing industry (upwelling areas are great
fishing grounds)
http://www.youtube.com/watch?v=3niR_Kv4SM
Conveyor and Climate Change
• Scientists are concerned that global
warming could affect the ocean
conveyor system and make abrupt
climate change more likely
WHY?
• Melting of ice is making polar seas less
salty, which could interfere with sinking
– slowing down the conveyor
• On the other hand, tropical waters are
becoming saltier and more dense
• Ultimate result…
Rip “Currents”?!
• Often called "riptides," but they are not true
“tides” because they are not caused by the
moon’s gravitational pull. Instead, they are
caused by the shape of the shoreline.
• May also be called "undertow," which describes
a current of water that pulls you down to the
ocean bottom. However, rip currents move along
the surface of the water, pulling you straight out
into the ocean, but not underneath the water's
surface.
Rip Currents Continued
• May be sudden and unexpected.
• A narrow, powerful current of water
running perpendicular to the beach, out
into the ocean.
• May extend 200 to 2,500 feet (61 to 762
m) lengthwise, and are usually less than
30 feet (9 m) wide.
• Can move 5 miles per hour (8 kph) or
faster.
Rip Currents Continued
• Rip currents are responsible for about 150
deaths every year in the United States.
• They are the number-one concern for
beach lifeguards: About 80 percent of all
beach rescues are related to rip currents.
• http://www.youtube.com/watch?v=hCZuYzNujI
Journal Entry
1. List the factors that affect ocean currents
2. Describe the ocean conveyer belt
3. Write a detailed paragraph outlining
beach safety guidelines based on what
you learned today (specifically related to
rip currents)