Ocean Waves, Currents, and Tides

Ocean Waves, Currents, and Tides 6th Grade Earth Science

Currents A current is a large stream of water that flows through the ocean Two types of currents Surface Currents Deep Currents

Surface Currents • Driven mainly by the wind • They follow Earth’s major wind patterns which move in a circular pattern Earth's wind and current patterns Why do the winds and the currents move in a circular pattern? The Coriolis Effect (Globe Demo)

Surface Currents • Due to the Coriolis effect, currents in the Northern Hemisphere curve to the right and to the left in the Southern Hemisphere. • The largest and most powerful surface current in the North Atlantic Ocean, the Gulf Stream, is caused by strong winds that blow regularly from the west. It carries more than 100 times the water of the mighty Mississippi river. It carries warm water from the Gulf of Mexico northward along the east coast of the U.S. As a result of the Coriolis effect, it curves north east across the Atlantic

Surface Currents • A surface current warms or cools the air above it, influencing the climate of the land near the coast. • Because of the warm waters of the Gulf Stream, a country as far north as England can have fairly mild weather. • The average winter temperature in Newfoundland, Canada is 15°F. In England the average winter temperature is 42°F. That’s a difference of 27°, all due to the Gulf Stream.

Surface Currents • At certain places on Earth, sometimes the wind patterns reverse, causing the surface currents to reverse directions. • One such reversal called El Niño happens about every 2 to 7 years and lasts for 1 to 2 years at a time. • El Niño starts when the wind pattern which usually blows towards the west reverses and blows east across the Pacific Ocean bringing warm waters with it. • Of course, this warm current warms the air above it causing more evaporation and therefore more storms for the western U.S. creating heavy rains, flooding, and mudslides in California and more tornadoes in Florida. El Niño

Deep Currents • Deep currents are caused by differences in the density of ocean water. • Ocean water density depends on its temperature and its salinity. • Cold water is more dense than warm water. • Saltier water is more dense than less saltier water. (Demos) • As warm surface currents near the poles the water cools and its salinity increases due to ocean water freezing and leaving the water near the poles more salty. (Page 384) • The cold, saltier water sinks and starts moving back towards the equator along the bottom of the ocean. • When the water reaches the equator, it warms and rises again. -Someone tell me what this self-powered system of cold water sinking and warm water rising is called? A C_ _ _ _ _ _ _ _ N C _ _ _ _ _ _ T • Deep currents flow slowly. They may take as long as 1,000 years to flow from pole to equator and back again.

Currents Coriolis effect El Niño warmer Surface direction evaporation 100 Gulf Stream _______________ ocean currents are caused mainly by winds that blow regularly in the same ___________. They can reach depths of several _____ meters. The largest and most powerful surface current in the North Atlantic Ocean is the __________ __________. This current takes a right turn east across the Atlantic due to the ______________ ____________. It warms the air above it, causing it to be _________ in England than it is in Nova Scotia, even though both of them are at the same latitude. Sometimes surface currents reverse, like the __________ ___________. When this happens, there is more ____________________, leading to more storms for the U.S.

Currents convection current salinity heat equator density temperature saltier Deep ocean currents are caused by differences in the __________ of ocean water. The density of ocean water depends on its ____________________ and _______________. As deep ocean currents reach the poles the water cools and gets ______________ which makes it denser causing it to sink. This cool water then flows across the bottom of the ocean back to the ______________ where it is warmed again starting the _____________ ___________ over again. This is the way that ___________ is distributed around the globe.

WavesThe four parts of a wave: Wavelength Trough Wave Height Crest

WavesCheck What You THINK You Knowwavelength, wave height, trough, crest 1 _____2_____ 3 4

Check What You THINK You Knowwavelength, wave height, trough, crest • What is the horizontal distance between crests ? • What is the lowest part of the wave? • What is the highest part of the wave? • What is the vertical distance between crest and trough?

Diagram of a Wave

Waves Waves start in the open ocean The size of a wave depends on the strength of the wind, the length of time that it blows, and the distance over which it blows Waves move energy, not water. The water in a wave does not actually move forward, just the energy generated by the wind. The wind affects the water at the surface more than it does the deep water. Let’s take a look at this in action: Wave Energy and Wave Size

Breakers • As waves approach the shore, the water becomes shallower. • The bottom of the waves begin to touch the sloping ocean floor. • Friction between the ocean floor and the water causes the waves to slow down. • As the speed of the wave slows down the shape of the wave begins to change • Near the shore wave length decreases and wave height increases. • When the wave reaches a certain height, the crest of the wave topples.

How Waves Affect theShore Longshore Drift • As waves come ashore, water washes up the beach at an angle, carrying sand grains. • Gravity causes the water and the sand to run straight back down the beach slope. Longshore Drift 1 Longshore Drift 2 Longshore Drift 3

Barrier Islands • Barrier islands like the one’s that stretch along the coast of Georgia are formed from deposition of sediments coming from Georgia’s rivers, and sand being deposited along the coastal side of the island by the longshore drift. • Because the wind and waves are constantly redistributing the sand these islands are not permanent. • They are constantly being reshaped.

Let’s see what you have REALLY learned! 1 _____2_____ 3 4 wavelength, wave height, trough, crest

Let’s see what you have REALLY learned! • What is the horizontal distance between crests? • What is the lowest part of the wave? • What is the highest part of the wave? • What is the vertical distance between crest and trough?

Surface Currents

Deep Currents

Tides • Tides are the daily rise and fall of Earth's waters on its coastlines • When water on the coast reaches its highest point it is high tide. • When water on the coast reaches its lowest point it is low tide. • Unlike surface waves, tides are regular and do not depend on wind. If not wind, then what causes tides? • Tides are caused by the interaction between theEarth, the moon, and the sun. • The gravity exerted on Earth's oceans by the moon and the sun cause the water to move from one side of the planet to the other side. • The moon is much closer to the Earth than the sun, so it exerts a greater gravitational effect on the tides. Gravitational effects of the moon and the sun on tides More

Tides • There are two high tides and two low tides about every 25 hours. • That means every six or so hours you have a high tide and then a bit more than six hours later you have a low tide. • Changes in the positions of Earth, the moon, and the sun affect the heights of tides during a month. If it is 7:45 A.M. in the photo on the left, what time is it in the photo on the right if it is still the same day? What time will the next high tide be?

Tides The sun is much bigger than the moon. Why doesn't the sun affect tides more than the moon? Why do the heights of the tides change during the course of a month? Is the water higher during a neap tide or a spring tide? If the low tide at location A occurs at 3:00 P.M., at what times will the next two low tides occur? Lab Zone Discover Activity on page 366 of your textbook.

Ocean Waves, Currents, and Tides