Ocean Currents
• The mass movement of __________________, either vertically or
horizontally, in the __________________
• Surface currents are __________________-driven movements of water at
or near the surface of the ocean
• Thermohaline currents are the slow, __________________currents that
affect the vast bulk of water beneath the __________________
• Named this because they depend on density differences caused by variations in
water’s temperature and __________________
Surface Currents
• About __________________ of the water in the ocean is involved in surface
currents
• A surface current includes the water that is flowing __________________in
the uppermost 1,300 ft
• Most surface currents move water above the __________________
• These currents are driven mainly by __________________friction
• Most of the wind energy is concentrated in the trade winds and
__________________
• Due to the forces of gravity, the __________________effect, solar energy,
and solar winds, water often moves in a circular pattern called a
__________________.
Surface Currents and the
Coriolis Effect
• Gyres in the N. Hemisphere
move __________________
• Gyres in the S. Hemisphere
move __________________
Gyres
• Surface currents flow around an ocean basin to create a gyre, which is
typically made up of __________________ surface currents
• Gyres flow continuously without obvious changes between
__________________
• The end of one current blends into the start of the next current
• Each current has distinct __________________ which is why each is
considered a separate current
• __________________ gyres are gyres in balance between the pressure
gradient and the Coriolis effect
• The geostrophic gyres are independent of one another due to wind
patterns and the positions of the __________________
Gyres
• There are ______ great surface circuits, but only 5 of these are
considered geostrophic gyres.
•
•
•
•
•
N. Atlantic
S. Atlantic
N. Pacific
S. Pacific
Indian Ocean
• The 6th circuit does not travel around an ocean __________________
(it travels around a continent) so it’s not considered a gyre
• Antarctic Circumpolar Current (aka West Wind Drift)
• Flows endlessly around __________________ and is driven by the Westerlies
Western Boundary Currents
• Found on the __________________ edge of each gyre (off the east
coast of a continent)
• __________________, deepest, and __________________ currents
• Move __________________ water from the __________________ to
the poles
• 5 of them:
•
•
•
•
•
Gulf Stream (N. Atlantic)
Kurashio Current (N. Pacific)
Brazil Current (S. Atlantic)
Agulhas Current (Indian)
East Australian Current (S. Pacific)
Eastern Boundary Currents
• Found at the __________________ edge of ocean basins (off west coast of
continents)
• __________________, slow moving, and __________________
• Carry __________________ water from poles toward
__________________
• There are 5:
•
•
•
•
•
Canary Current (N. Atlantic)
Benguela Current (S. Atlantic)
California Current (N. Pacific)
West Australian Current (Indian)
Peru Current (S. Pacific)
Transverse Boundary Currents
• Most of the power for currents is derived from the __________________ at
the fringes of tropics and from mid-latitude __________________
• The stress of winds on the ocean in these bands gives rise to the
__________________ currents
• These currents flow from east to west and west to east, linking the
__________________ and __________________ boundary currents on
both the north and south ends of each gyre.
Transverse Currents
Ekman Spiral
• So in a gyre, why does water flow around the periphery of the ocean basin
instead of spiraling to the center?
• Not only does the __________________ play a role in this movement, so
do __________________ patterns
• When driven by the __________________, the topmost layer of ocean
water in the N. Hemisphere flows at about 45˚ to the right of the
__________________ direction.
Ekman Spiral
• What about the water below the top layer?
• The lower layers can’t “feel” the wind at the surface; However, it “feels”
only the movement of the water immediately __________________
• The deeper layer of water moves at an __________________ to the right of
the overlying water (due to __________________ )
• The same thing happens in the layer below that and so on and so on
• This continues to happen until a depth of about __________________
• This process is known as __________________
Ekman Spiral
• Even though its known as the
Ekman Spiral, the water itself is
not __________________ .
• The term spiral refers to what
you would see on a diagram
Ekman Transport
• Ekman __________________ = the net motion of __________________
down to about __________________ after the allowance for the summed
affects of Ekman spiral
• In theory, the direction of Ekman transport is _________ to the right of the
wind direction in the N. Hemisphere and 90˚ to the left in the S.
Hemisphere
• In actuality, the Ekman transport in gyres is __________________
• This difference is caused by the interaction of the __________________ effect and
the pressure gradient
Ekman Transport
So, why doesn’t the water spiral to the center of each
ocean basin?
• There are hills of water at the center of
each ocean basin
• In order for the water to spiral toward the
center, it would have to “climb” this hill
and go against the __________________
Countercurrents and Undercurrents
• __________________
• Usually found near __________________ currents
• Flow on the surface in the __________________ direction of the main current
• Caused by the lack of persistent __________________ at the equator
• __________________
• A countercurrent that occurs beneath the __________________ currents
• Found under most major __________________
Surface Currents and Climate
• Surface currents (along with wind) distribute tropical __________________
worldwide
• Warm water flows to higher __________________ , transfers heat to the air
and cools, moves back to low __________________ , and absorbs heat
again
• The climate along a coastline greatly depends on the nearby surface current
• A warm current typically leads to a warm and humid __________________ (Florida
and any of the Gulf states)
• A cold current typically leads to cooler __________________ with lower
__________________ (California and the other west coast states)
Vertical Movement of Water
• The wind-driven horizontal movement of water can sometimes cause
__________________ movement of water
• The movement is called wind-induced __________________ circulation
• 2 types
• __________________
• __________________
Upwelling
• Upwelling is the __________________ movement of water
• The water from within and below the __________________ is often rich in
the __________________ needed by marine organisms for growth
• __________________ upwelling - friction of wind blowing along the ocean
surface __________________ to the shore causes water to begin moving,
the Coriolis effect deflects it to the right and the resulting Ekman transport
moves it off shore
• Fuels __________________ productivity (__________________)
• __________________ upwelling - water moving in the currents on either
side of the equator is deflected slightly __________________ and replaced
by __________________ water
Coastal Upwelling
Equatorial Upwelling
Downwelling
• Water driven toward a coastline will be forced __________________ ,
returning seaward along the continental shelf
• Helps supply the deeper ocean with dissolved __________________ and
__________________
• Moves __________________ gas from the photic zone to the aphotic zone, which
assists in distribution of living __________________
• Has no direct effect on __________________ or productivity of the coast
Downwelling
El Niño vs Normal
• Conditions during a normal year (a non-El Nino yr):
• Surface winds across most of the tropical Pacific normally move from
__________________ to __________________
• Trade winds blow from the normally __________________ area over the eastern
Pacific (S. America) to the normally stable __________________ area over the
western Pacific (N. Australia)
• Strong __________________ currents in the western Pacific
• Nutrient rich waters off the coast – leads to great biological __________________
• Sometimes these conditions are __________________ for unknown
reasons
• Occurs at irregular intervals of roughly 3-8 yrs
El Niño - The Conditions
• Conditions during an El Nino year:
• Pressure systems __________________
• High pressure builds in the western Pacific; low pressure dominates the eastern
Pacific
• Winds across the tropical Pacific reverse direction and blow from
__________________ to __________________ ; the trade winds either
__________________ or reverse
• The change in atmospheric pressure is called the Southern Oscillation
El Niño – What are the Effects?
• The reversed winds move the __________________ waters from the
western Pacific to the eastern Pacific
• The eastern Pacific is greatly affected:
• Disrupts __________________ which causes a change in nutrients found in the
waters, which affects the animals living in the area – they either die or migrate
• Causes high __________________ in normally dry areas
• Coastal storms are intensified
• Sea levels can rise up to __________________
• Water temp can increase up to __________________
• How is the western Pacific affected?
• Long periods of __________________
• Crops don’t grow; people starve
Non El Niño Year
El Niño Year
Animations of Normal vs El Nino vs La Nina:
http://esminfo.prenhall.com/science/geoanimations/an
imations/26_NinoNina.html
https://www.youtube.com/watch?v=Ct1fXhTv3UA
La Niña
• Normal circulation returns with surprising __________________
• Produces strong __________________ , powerful __________________ ; chilly and
stormy conditions along S. American coastline
• The powerful return that causes colder than normal events is called
__________________
• As conditions in the eastern Pacific cool off, the ocean in the western Pacific
__________________ rapidly
• Trade winds become stronger than normal resulting in above average
__________________ in the eastern Pacific
• Increased __________________ pushes cold water further out into the Pacific,
pushing the warm waters closer to the edge of the western Pacific
Thermohaline Circulation
• Thermohaline circulation is the movement of water due to
differences in __________________
• This type of circulation is mainly found below the
__________________ in the deep zone and moves water
__________________ and __________________ within this zone
• This process is responsible for the large-scale vertical movement
of ocean water and the __________________ of the global ocean
as a whole
Thermohaline Circulation
Water Masses
• Each water mass has specific __________________ and
__________________ characteristics
• These differences prevent __________________ from easily
mixing with each other
• Water masses usually flow __________________ or beneath each other
• These differences also lead to __________________ stratification
of the ocean
Water Masses
• Water masses are named according to their __________________ position
• In temperate and tropical waters, there are 5 layers:
• __________________ water – goes to a depth of about 200 meters
• __________________ water – from approx. 200m down to the bottom of the
thermocline
• __________________ water – from bottom of thermocline down to about 1500m
• __________________ water – water below the intermediate water, but not in
contact with the bottom (to a depth of approx. 4000m)
• __________________ water – water in contact with the ocean floor
• These layers don’t exist near the poles.
• Why?
AAIW = Antarctic Intermediate Water
AABW = Antarctic Bottom Water
NADW = N. Atlantic Deep Water
Studying Currents –
Float Method
• Depends on the movement of a __________________ bottle or other freefloating object
• Drift bottles and drift cards – for __________________ currents
• Especially useful in determining __________________ circulation
• Do not record the path taken
• Drift __________________ – for surface currents
• Path can be tracked for more __________________ circulation patterns
• Tracked by __________________ or satellite
• __________________ float – for intermediate currents
• Detects the drift of __________________ water masses
• Descends to a specific __________________
• Emits sonar “pings” as it drifts so that it can be tracked
Studying Currents –
Flow Method
• Flow meters measure the
__________________ and
__________________ of a current
from a fixed or stationary position
• Ekman flow meter
• Uses rotating vanes to measure
speed and a recording
__________________ to measure
direction
Studying Currents –
Slocum Glider
• A glider that “flies” smoothly up and down through the water
__________________
• Collects data on __________________ , salinity, density,
__________________ and speed of __________________ water currents
• Powered by __________________ and buoyancy
• Reach the surface periodically to transmit data to satellites before returning
to the depths of the sea to collect more data
• Can spend __________________ at sea before being collected