1. Ocean Currents & Climate
The ocean and its currents have a major influence on weather and climate on Earth.
In this unit we will see how interactions among the hydrosphere, lithosphere, atmosphere, and the ocean produce weather and climate changes.
On the following slides, the green sections are the most important.
Underline words = vocabulary!
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2. Global Warming Pre-Test
Last week you took a global warming pre-test to test your prior knowledge on the subject of global warming.
Let’s review your scores!
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3. Currents
The major landmasses on Earth are connected by moving water called ocean currents.
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A current is a large mass of continuously moving ocean water.
The largest currents that move across the ocean are called global ocean currents. These currents are like rivers that travel great distances.
Ocean currents are affected by global temperature, freshwater glacial ice melt, and density differences due to salt concentrations and temperature differences.
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4. Greenhouse Effect
The atmosphere of our Earth acts like a greenhouse that traps heat; the energy from the sun also heats up the oceans.
50% of radiation from the sun is absorbed by the Earth’s surface and then “bounces” back into the earth’s atmosphere.
Gases, such as carbon dioxide and water vapor, can stop this energy from escaping into space by keeping it here on Earth.
As a result, the Earth’s atmosphere stays warm, this is termed the greenhouse effect.
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5. Global Warming
Scientists have noticed that the Earth is experiencing a warming trend.
In the past 100 years, the Earth’s mean global temperature has increased more than 1 degree Celsius and ocean levels have risen approximately 10 cm.
Global warming is the result, the gradual increase in Earth’s temperature.
Scientists are trying to measure polar ice caps to determine if their rate of melting continues to increase.
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6. Measuring the Melt
Scientists around the world provide research based data on the effects of increased global temperatures.
Specific data includes measuring the levels of artic ice.
The graph below shows total ice coverage since 1973.
As glacial ice melts, sea levels rise and ocean currents can change.
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7. Carbon Dioxide levels
The burning of fossil fuels (oil, coal, etc) also adds carbon dioxide to the environment.
Air pollution produces by humans is adding to the problem of global warming.
The amount of carbon dioxide in the atmosphere has been steadily increasing.
As we continue to cut down trees for paper production, we are decreasing the plants that convert CO2 to oxygen, causing an increase in CO2 levels.
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8. Natural Air Pollution Even “clean” air is not perfectly clean.
It contains many pollutants from natural sources like dust, volcanic gases and ash, smoke from forest fires, pollen, etc.
Most of the air pollution mentioned in the news is a result of human activities.
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9. Natural Cycle?
Throughout the history of Earth the climate has gone through periods of warmth and periods of extreme cold (often known as an Ice Age). This is a natural phenomenon.
Some scientists claim that the warming trend is part of a natural cycle that will eventually reverse itself through CO2 uptake by photosynthetic marine and terrestrial plant life.
Others claim that the warming of Earth’s atmosphere is a real problem that can be reduced by decreasing the use of fossil fuels and finding alternative energy sources.
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10. Review of Water
What does this shape represent? The most basic compound necessary for all life on Earth is water.
The symbol for water is H20, or shorthand for two hydrogen atoms and one oxygen.
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11. Review of Water, Cont.
The compound water (H2O) becomes stable by sharing the valence electrons between the atoms.
What is the atomic number for oxygen? 8!
So how many electrons are in the outside shell? 6!
What is the atomic number for hydrogen? 1!
The electrons from hydrogen fill in the openings in the shell of oxygen.
The two wind up working together and share electrons to form water!
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12. Water’s Polarity.
The different charges on the water molecule make it a polar molecule (different charges at different poles).
It is shaped in this manner because it is polar. Think magnets! They push apart!
The oxygen atom takes on two more electrons to become stable (making it slightly negative).
The hydrogen atoms give up electrons making them slightly positive.
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13. Water’s Density
Density is the process by which molecules are packed closely together.
Warm water has a higher density than cold water due to the increased kinetic energy of the molecules (they are moving fast, creating more pace – thus, they rise).
Fresh water is less dense than salty water.
Density is important to the currents which shape the planet’s climate.
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14. Effect of Salinity
Salinity, or the amount of salt within a solution, changes the density of the water.
Salty water will sink while fresh water will rise because of differences in density.
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15. In the Mediterranean
The Mediterranean Sea, for example, has a higher salinity than the Atlantic Ocean, creating a current south of Spain that moves salty water deep into the Atlantic Ocean.
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16. Global Ocean Currents Observe the Image of the major global currents.
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17. Radiant Energy
The sun, the source of all energy on Earth, gives off radiant energy and influences the climate that we experience.
The amount of radiant (or solar) energy that reaches any part of the planet depends on the angle at which the rays of the sun strike the surface. (Angle of Isolation)
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The Earth’s curved surface and the tilt of its axis causes areas farthest away from the sun’s rays (the poles) to receive slanted rays with a smaller angle, and are therefore less intense.
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18. Ocean Temperature
The uneven heating of the Earth due to the rays of the sun causes ocean temperatures to vary with latitude.
The ocean is warmest at the equator.
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19. Coriolis Effect
The coriolis effect states that the spinning Earth causes the winds and surface waters to move in a specific directions.
In the northern hemisphere, the currents deflect clockwise to the east.
In the southern hemisphere currents move in the opposite direction, counter clockwise to the west.
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20. Gyres
The water moves and hits the continent which deflect the currents, causing them to move in giant circles called gyres.
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21. Gulf Stream
The gulf stream current flows from the southwestern Atlantic to the northeastern; it is the major factor in favorable (warm) weather on the eastern coast of the United States.
Benjamin Franklin was the first to chart the temperature and speed of the gulf stream back in the 1700s.
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You can see that the gulf stream flows northeast up the coast of the United States. The satellite image shows it carries with it very warm water.
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22. Subsurface Currents
Subsurface currents, or currents beneath the surface of the ocean, move because of differences in temperature and salinity.
Where would warm water go if it was mixed with cold water? Fresh with salt?
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23. Downwelling & Upwelling
After warm water has risen to the surface, it will eventually cool off and therefore sink again near the poles (downwelling).
When currents rise to the surface, they bring nutrient-rich sediments from the bottom. The rising of such waters from the deep ocean is called an upwelling.
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Nutrients found on the floor of the ocean (such as phosphates & nitrates) are important for all organisms in aquatic food webs.
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24. Coastal Currents
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Currents eventually meet coastal areas creating waves.
After a wave breaks on a beach, the forward momentum transports water up the slope of a beach. The returning current or backwash is called the undertow. An undertow is an example of a current cased by wave action.
Currents that move parallel to the beach are called longshore currents.
Spaces between islands off the coast of a continent, like Galveston and South Padre, cause a rush of water called a rip current that moves quickly out into the ocean.
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25. Tidal Currents
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The movement of the moon around the Earth and it’s gravity causes tides, or the daily rise and fall of the ocean seen along the shore.
When a tide enters and leaves and area, the tidal change produces swift-moving tidal currents that run parallel to the shore.
These currents are important to aquatic food chains because they carry nutrients and small organisms back and forth between the bays and the offshore waters.
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26. Ocean Wind
Convection currents occur in many different media (liquid, air, magma).
Often, the wind (or a mass of moving air) around the ocean creates a sea breeze due to differences in temperature of the air over the ocean versus over land.
Water heats up slowly, while land heats up quickly.
A convection current is created because the cooler air over the ocean sinks and travels inland while the warm air over the land rises up.
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27. Ocean wind cont.
The opposite occurs at night; land cools very quickly, but water has a very high specific heat (or heat storage ability) and takes longer to cool.
The air, therefore, over the water is warmer and wind travels out to the ocean in the reversed convection current.
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28. Humidity
The ocean influences not only air temperature but also sends a large amount of water vapor into the atmosphere, measured as humidity.
Coastal regions often have a higher level of humidity than inland areas because they are exposed to the moisture that evaporates from the ocean.
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29. Fog & Dew
Air at sea level in many coastal regions is often filled with so much moisture it looks like a low flying cloud.
Air saturated with moisture creating clouds near the ground is called fog.
Fog forms when warm, moist air makes contact with a cold surface.
The mirror in your bathroom often “fogs” when warm moist air from the shower hits the cold surface of the mirror.
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When water condenses (changes from a vapor to a liquid) on a solid surface it is called dew. Dew is moisture that comes from the warm air and condenses on a cold surface.
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30. Hurricanes
A hurricane is a coastal storm with a wind velocity exceeding 120 km per hour.
Hurricanes form in warm tropical seas where there is hot, moist air. Such conditions contain the heat needed to fuel a hurricane.
As hot, moist air rises, it cools in the upper atmosphere and condenses into ring shaped clouds. During condensation, a great deal of heat energy is released, which causes more hot air to rise even quicker. This whirlwind of rising air moves in a spiral direction around calm air knows as the “eye” of a hurricane.
View the animation from NASA by clicking the graphic.
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31. El Nino
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Droughts in Australia, famine in Africa, floods in California, and other climate disturbances in recent years have all been caused by changes in the warm ocean currents around the globe.
Oceanic warming is called El Nino.
El Nino begins in the western Pacific Ocean.
Warm currents are normally carried northwest due to trade winds.
El Nino reverses the currents because of a decline in southeast trade winds and causes a change in the climate of South America (bringing floods and stormy weather).
Follow the arrows in the image above.
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32. La Nina
Unusually cold currents causing cooler surface temperatures is known as La Nina.
During La Nina years (when ocean currents are unusually cool in the mid-Pacific) winters are cooler than normal in the northwest United states and warmer than normal in the southeast.
The cycles for El Nino/La Nina often last 1 to 2 years and occur every 4 to 6 years. Click on the graphic to view an animation depicting the differences between El Nino and La Nina.
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33. Conclusion
Ocean currents on planet Earth drive the weather and stabilize the climate.
Changing of ocean currents and related factors such as trade winds can have devastating effects (El Nino, La Nina, rising sea levels, etc).
In order to understand the complex factors that create Earth’s climate you need to understanding the forces of density, salinity, and Earth’s temperature as they relate to ocean currents.
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34. Possible Effects Journal: Future of Global Warming
Using the political cartoon at the left, predict earth in the future and explain why the cartoonist chose to use the image to image a future earth after global warming. Is this a possible effect of an increase in global temperatures?
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