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The Oceansor: Why It’s So Freaking Cold Down
ThereChapter 15
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Where did the oceans come from?
• Two sources• Comets (frozen water &
gas balls) collided with Earth and released their water• Meteorites that collided
with Earth during its formation contained water
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• Volcanism brought water vapor into the atmosphere
• Water vapor condensed as the Earth cooled• Condensed water rained
down to the surface
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What are the oceans?
• Recall: the hydrosphere is all of Earth’s water combined (including ice)• Oceans make up 97% of all
the water on Earth.• Oceans cover 71% of
Earth’s surface.
• The oceans are really one connected body of water.• The ocean is salty, not pure
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• Major oceans• Pacific• Atlantic• Indian• Antarctic
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• Seas• Part of same landmass as
oceans• Smaller than oceans• Partially or mostly
landlocked• Examples:• Aral Sea• Mediterranean Sea• Gulf of Mexico• Bering Sea
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• Sea ice• Sea ice is constantly
changing• Grows during winter• Shrinks during summer
• Ice is less dense than water so it floats• This helps insulate the
oceans and prevent them from freezing entirely
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What are the properties of sea water?
• Salinity• Salinity is a measure of
the mass of dissolved salts per mass of water• Measured in parts per thousand (ppt) or percent• Recall that percent
means parts per hundred
• Sea water has an average salinity of 35 ppt or 3.5%
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ocean salinities
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• Salinity varies from place to place• Evaporation increases
salinity• Precipitation & melting
sea ice decrease salinity
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• Temperature• The sun heats the ocean• Water heats up (& cools
down) more slowly than air or land• So, the ocean acts as an
insulator—it resists major changes in temperature• This is why coastal
areas have smaller swings in temperature between seasons.
• Different areas of the ocean heat up at different rates• This causes convection
currents.
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map of ocean surface temperatures
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ocean temperature vs. depth
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• Ocean temperatures range from -2C to 30C.• Average surface
temperature is 15C• Temperature decreases
with depth• The deep ocean is always
cold, everywhere on the globe• Surface temperatures vary
more because of differences in sun exposure
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• Light absorption• Water absorbs light• Red light gets absorbed
first, in shallow waters• Blue light gets absorbed
last, in deep waters• Almost no light
penetrates below 100 meters
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light absorption at various depths
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What are water masses?
• The ocean is separated into layers because of different densities
• Temperature & salinity affect density• Colder, saltier water is
denser and sinks• Warmer, less salty water is
less dense and floats• A thermocline is an area
where water rapidly decreases in temperature with depth• A halocline is an area
where water rapidly changes salinity with depth
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ocean layering - temperature
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• Cold water comes from the polar seas and migrates along the sea floor toward the equator• Antarctic Bottom Water:
from freezing Antarctic seas• North Atlantic Deep Water:
from Greenland• Antarctic Intermediate
Water: from winter water in the Antarctic Water
• Colder water pushes warmer water toward the surface
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major water masses
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• Currents affect the locations of different layers
• Living organisms are adapted to specific ocean layers• Plants are found only in the
sunlit zone• Most organisms live close to
the surface
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organisms & ocean zones
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How does the ocean move?
• Waves• A wave is a rhythmic
movement that carries energy through ocean water.• Waves are causes by wind
or earthquakes.• The water moves up &
down in circle, but the energy moves forward.• Waves break when they
experience friction against the ocean floor in shallower water.
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waves moving & breakinganimation
• Animation will open in an external window (exit slideshow to view)
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• Currents• A current is the
movement of a body of water in a definite direction• Density currents are
caused by differences in density• Ex. Antarctic Bottom
Water sinking• Surface currents are driven
by wind• Ex. Trade winds in the
tropics blow from east to west and push tropical waters from east to west
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• Surface currents cause upwelling—the movement of lower waters toward the surface
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• Gyres• A gyre is a circular
current• Gyres are the result of
currents being deflected by continents• There are five major
gyres
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• Coriolis effect• The Coriolis effect is the
deflection of water (and air) to the right above the equator and to the left below the equator• It is caused by Earth’s
rotation• The Coriolis effect causes:• Clockwise gyres in the
northern hemisphere• Counterclockwise gyres in
the southern hemisphere• Remember that continents
deflect this movement!
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The Coriolis Effectanimation
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• Tides• Tides are the periodic rise
and fall of sea level.• The difference between
high and low tide (tidal range) varies from place to place.
• Tides are caused by the gravitational attraction among the Earth, moon, and sun.• The moon & sun pull on
Earth’s oceans.• High tide occurs where the
oceans bulge.