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9.8 Oceanography: 4. Mass motion
| Syllabus reference: (October 2002 version) | ||
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| 4. The mass motion of oceans |
Students learn to:
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Students: |
Extract from Earth and Environmental Science Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW.
[Edit: 3 June 11]
Prior learning: Oceanography, 9.8.1, 9.8.2 and 9.8.3.
Background: With increased population, and people wanting a higher standard of living more pollutants are being produced. On the other hand people are more aware of the necessity to protect our environment. Hopefully with a better understanding of ocean currents and more awareness of the destruction that can be a result of tsunamis, officials and ordinary people can make a greater effort to protect humans and the environment.
present information that identifies structures found in deep-sea organisms that are inferred adaptations to environmental conditions
A lot of research has been done with submersibles in the last twenty years and new organisms are constantly being discovered. Below are some websites for deep sea research or you might like to find your own.
- This one has information on a giant deep sea isopod and also has links to other organisms. JD Knight, Sea and Sky,
Orlando, Florida, USA
- This is an article from the BBC on a colossal squid found in Antarctic waters Super squid surfaces in Antarctic, by Kim Briggs, Wellington, New Zealand, BBC News
- This has diary entries for the ocean explorer but isn’t so good on
adaptations.
Operation Deep Scope 2005, NOAA (National Oceanic and Atmospheric Administration),
USA
When you have enough information, present it to the class. You might use a power point presentation or use photographs and notes.
describe the four types of mass motions of water:
- surface currents
- deep circulation
- tides
- tsunamis
and identify the energy source for each
Ocean currents or the mass motion of water are affected by:
- thermal expansion and contraction of water
- wind blowing over the water caused by differential heating of the Earth’s surface and
- density differences between water layers.
Other forces that have a lesser affect and influence the direction and nature of the flow of currents are:
- the Coriolis effect
- gravity
- friction and
- the shape of the ocean basins.
Surface Currents
- Surface currents can be described as the horizontal flow of water at the ocean’s surface. Surface currents are driven predominately by wind patterns. As the wind blows across the surface of the ocean, it drags the water with it.
- The main direction of movement 30 o north and south is towards the equator
and from these latitudes towards the poles, the wind blows towards the poles.
This movement is complicated by the rotation of the earth which results in
the Coriolis effect. There is also an east-west current along the equatorial
regions, in both the northern and the southern hemispheres.
A concise and simple map shows the currents much better than using words. National Maritime Museum, Royal Observatory, Greenwich, UK - When continents restrict surface currents gyres are formed. Gyres are closed circular patterns caused by continents that restrict the free flow of ocean currents. In the southern hemisphere this flow is anticlockwise and in the northern hemisphere it is clockwise.
Deep Circulation
- Thermohaline (temperature and salinity) circulation occurs at great depths within the ocean and is driven by density differences within the ocean’s waters.
- The majority of the Earth’s oceans are involved in slow thermohaline circulation which results in most of the vertical motion of the ocean water.
- Cold, saline waters formed at the poles sink and move away from the poles, drawing warmer surface water towards the poles. This drives deep ocean currents in a giant circulating system called the global conveyer Science@NASA , The science mission directorate, USA
Tides
- Tides are the periodic, short term changes seen in the height of the ocean’s surface.
- They are caused by the combined gravitational force of the moon and the sun and are affected by the motion of the Earth.
- They act in a generally predictable way.
Tsunamis
- Tsunamis are ocean waves generated by rapid displacement of ocean water usually caused by factors such as seismic activity, landslides, volcanic eruptions and icebergs falling from glaciers.
- Tsunami have a long wavelength and usually a small amplitude, however, they travel at high speeds and transfer large amounts of energy to coastal areas they encounter.
- Tsunami formed within confined areas such as a bay can be very destructive.
This video shows the series of waves coming towards the coast. Japan Earthquake: Helicopter aerial view video of giant tsunami waves
This covers more of the science behind the Japan Tsunami FAQ: What’s the Science Behind Japan’s Quake and Tsunami?
explain how the oxygen supply on the ocean floor is renewed, making life there possible
- Oxygen is dissolved in water when waves crash on rocks and beaches and when fresh water that has been flowing quickly over rocks and waterfalls, flows into the ocean. Oxygen is produced in oceans when plants, algae and phytoplankton photosynthesise, releasing the oxygen into the water.
- Some of this oxygen is then transported down to the ocean floor on vertical currents. It may be carried on the surface for some time until conditions are such that the water sinks.
- Another source of oxygen is the chemosynthetic bacteria that live near vents at mid ocean ridges. Some are free living and others are symbiotic, living in the tissue of animals such as tube worms. They use hydrogen sulphide from the vents to fix carbon dioxide to produce carbon based molecules. These can be absorbed by the tube worms. In the process oxygen is produced.
explain how long-lived materials, such as synthetic chemicals and heavy metals, that enter the sea in one place can be found thousands of kilometres away
- Mercury and lead are two dangerous heavy metals being dumped into our oceans.
- These heavy metals are often absorbed onto fine sediments suspended in
the ocean waters. They can then be transported thousands of kilometres around
ocean basins by currents.
- They can also be taken up by marine organisms close to dump sites. These marine organisms form part of ocean food chains and so can be found far from where they originated and can be concentrated in organisms that are top consumers in the food chain.
process information to explain why laws about the ocean are becoming increasingly important in the world society
- Obtain information from your teacher and use the web links below.
- Oceans and law of the sea
United Nations Convention on the Law of the Sea of 10 December 1982
- On High Seas, No Easy Answer To Pirates
Use Of Armed Escorts Called Shipriders Raises Host Of International Legal Dilemmas, CBS News, World
- Oceans and law of the sea
- For more information go to a search engine and type words such as ‘ocean’ ‘pollution’ ‘fishing’ ‘laws’ ‘environment’ ‘protection’ ‘safety’.
- Illustrate trends and patterns by organising the data through the selection and use of appropriate methods.
discuss the implications of the movement of materials by ocean currents for the use of the oceans for waste disposal, including:
- pollution
- ocean sewage outlets
- People thought the ocean’s great volume and continuous motion and mixing would dissipate and distribute natural and synthetic substances highly effectively. They argued in favour of deep-ocean dumping, because the material is diluted as it sinks, and remains stable on the sea floor. They also thought there wasn’t much diversity in the deep oceans so it didn’t matter if the ocean was a dumping ground for human wastes.
- The present body of research, however, suggests that dilution does not completely abate the effects of dumping, nor does the waste sit still once it gets to the bottom.
- Ocean dumping was banned in USA in 1989 and is currently generally banned worldwide yet few marine organisms are completely free of the effects of ocean pollutants. Most natural and artificial wastes - such as sewage sludge, mining tailings, ash from power stations, dangerous synthetic organic compounds and packaged goods - make their way to the sea floor over time.
- Research is being done to determine the extent of contamination currently present within certain sections of the oceans.
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