Due (mostly) to density the ocean is layered
 Remember that density of water depends on:
 Temperature ( temp = density)
 Salinity ( salinity = density)
 Pressure (minimal effect in the oceans)

Since the ocean layers (mostly) depend on density – what causes the density of water to change?
 Change In Temperature
 Change in Salinity

 Salinity
 Inflow/Outflow Of Water
 Rain & Rivers add fresh water (decreases salinity)
 Evaporation – removes water but leaves salt behind
(increases salinity)

 Salinity
 Freezing/Thawing Of Ice
 Thawing – adds fresh water (decreases salinity)
 Freezing – removes water but leaves salt behind (increases salinity)

In addition to the 3 variables that influence density, ocean layering is also due to
Movement Due To Wind
Now back to density…

Notice how density changes based on temperature and salinity.
Notice how different combinations of temperature and salinity can make the same density!

The ocean is stratified (layered) into three zones based on the density of seawater.
 The upper layer is called the surface layer or mixed layer.
 Extends from the surface to a depth of 500 feet.
 This layer contains the least dense water in the ocean.

 The middle layer, as defined by water density, is called the pycnocline.
 The pycnocline is an area where density changes rapidly with depth.
 This rapid change in density is directly related to the rapid change in temperature
(thermocline) and salinity
(halocline) in this layer.

 The bottom layer is called the deep zone
 It extends from the bottom of the pycnocline to the seafloor.

 In this layer, temperature varies little with depth and is very cold. Salinity in the deep zone is also constant and averages about 3.5%.
 Because of the cold temperatures, we find that the deep zone has the most dense seawater.

DENSITY COLUMN
Stable Column of water =
 Low density on top with high density below.
Low density
High density

DENSITY COLUMN
Unstable Column of water = high density on top with low density below.
 Unstable columns can not persist!
 The column will be overturned.
 .
High density
Low density

DENSITY COLUMN
Isopycnal = Neutral Stability = even density throughout
Low density High density

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te.org/noaa/lesson08.html

There are two types of currents –
 Deep Water Currents
 Due to density (temperature and salinity)
 Surface Currents
 Due to wind (speed and direction), Coriolis Effect and
Deflection (bumping into land)

Funniest one

a.Surface currents, driven by wind, move warm, less dense water toward the poles

a. Downwelling - The water cools and sinks b.The cold current runs along the ocean floor

d
. Upwelling – a sort of vacuum is formed from surface currents causing cold dense water to rise

 These are important because they allow for:
 Continuous movement of water – AKA Continuity of Flow
 Also…
 Downwelling – brings Oxygen from the surface to the deep
 Upwelling – brings nutrients and minerals from the ocean deep to the surface.

Downwelling and upwelling refer to vertical motion
Sometimes small downwellings and upwellings can be caused by winds on the surface.
• When wind pushes water together this
convergence causes a downwelling
• When wind pushes water apart this divergence causes an upwelling

There are two types of currents –
1) Deep Water Currents
 Due to density (temperature and salinity)

2) Surface Currents
 Due to wind (speed and direction), Coriolis Effect and
Deflection (bumping into land)

Surface ocean currents, which occur on the open ocean, are driven by a complex global wind system.
To understand the effects of winds on ocean currents, you need to understand the Coriolis force and the Ekman spiral.

If the Earth did not rotate and remained stationary, the atmosphere would circulate between the poles and the equator in a simple convection current.

Because the Earth rotates, circulating air is deflected.
The air deflects toward the
right in the Northern
Hemisphere and toward the left in the Southern
Hemisphere, resulting in curved paths. This deflection is called the
Coriolis effect.
Toilet bowl?

Warm air around the equator rises and flows toward the poles. As the air moves away from the equator, the Coriolis effect deflects it. It cools and descends near 30 degrees latitude. The descending air blows back toward the equator. This pattern repeats creating the wind belts shown.
Drawn winds on the board.
3 colors. (15 min)

Winds drag on the water’s surface causing it to move in the direction that the wind is blowing.
The Coriolis Effect causes the deflection of major surface ocean currents to the right in the Northern
Hemisphere (in a clockwise spiral) and to the left in the Southern Hemisphere (in a counter-clockwise spiral).

The blue line (1) shows the movement of the wind.
This pulls the surface water (2).
The surface water then pulls on the next level down in the water table.
However, the Coriolis Effect (4) pulls the water at a 90º angle.

The combined effects of the pulling of the surface currents (2) and Coriolis Effect (4) results in the water actually moving like
(3) at a 45º angle to the layer of water above it.
This pattern continues resulting in a spiral. The deeper you go in a spiral the slower the water moves.

Gyres = major spirals of ocean-circling currents
 Occur North and South of the equator.
 Do NOT occur at the equator where the Coriolis effect is not present.
 There are five major ocean-wide gyres
 North Atlantic
 South Atlantic
 North Pacific
 South Pacific
 Indian Ocean

Speed of water is measured in knots
 1 knot = 1 nautical mile/hour
 Where did the term come from?
Surface currents in the open ocean move at a rate of .25 to 1 knot.
Surface currents move faster when water is forced through narrow spaces.

Western Intensification = currents along the west turn of a gyre are strong, swift, and narrow due to the Coriolis Effect

Eddies are swirls of water that break off of a current.
They spin in the opposite direction and can be due to obstacles or wind.

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te.org/noaa/lesson10.html

1.
Who wrote “time and tide wait for no man”?
2.
Where else do tides occur other than the oceans?
3.
What is the term used to measure the difference between high and low tide?
4.
What exerts twice as much tidal force on the oceans than the Sun?
5.
When the Sun and the moon are at right angles to each other, what type of tide occurs on Earth?
6.
What is the highest point in a tidal zone called?
7.
How do sea stars adapt to the pounding surf?