the oceans or: why it’s so freaking cold down there

The Oceansor: Why It’s So Freaking Cold Down

ThereChapter 15

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

• Volcanism brought water vapor into the atmosphere

• Water vapor condensed as the Earth cooled• Condensed water rained

down to the surface

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

• Major oceans• Pacific• Atlantic• Indian• Antarctic

• Seas• Part of same landmass as

oceans• Smaller than oceans• Partially or mostly

landlocked• Examples:• Aral Sea• Mediterranean Sea• Gulf of Mexico• Bering Sea

• 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

sea ice thickness vs. timeanimation

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%

ocean salinities

• Salinity varies from place to place• Evaporation increases

salinity• Precipitation & melting

sea ice decrease salinity

• 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.

map of ocean surface temperatures

ocean temperature vs. depth

• 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

• 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

light absorption at various depths

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

ocean layering - temperature

• 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

major water masses

• 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

organisms & ocean zones

creatures of the deep seavideo clip

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.

waves moving & breakinganimation

• Animation will open in an external window (exit slideshow to view)

• 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

major ocean currentsanimation

• Surface currents cause upwelling—the movement of lower waters toward the surface

• Gyres• A gyre is a circular

current• Gyres are the result of

currents being deflected by continents• There are five major

gyres

• 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!

The Coriolis Effectanimation

• 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.

effect of sun & moon on tides

animation