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9.8 Oceanography: 8. Collection of data about the oceans
| Syllabus reference: (October 2002 version) | ||
| 8.Oceanographers have a range of technology available to assist the collection of data about the 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:8 August 08]
Background: From simple methods such as using sound reflection and dropping down a bucket to scoop up sediments on the ocean floor, there are now advanced technologies such as using satellites, submersibles and magnetometers to learn more about the deep ocean and the organisms that live there.
identify two of the following technologies used by oceanographers, and for each one, describe how they work and the evidence they provide:
- echo sounders
- dredges, grabs and core samplers
- fish and plankton nets
- bathythermographs
- magnetometers
You only have to research TWO technologies used by oceanographers so choose two from the following.
Echo Sounders
- These transmit sound waves that bounce off the ocean floor to measure the depth of the ocean. Echo sounding is based on the principle that water is a good medium for the transmission of sound waves and that a sound pulse will bounce off a reflecting layer, returning to its source as an echo. Scientists use the time interval between the sending of a sound pulse and echo returned from the bottom to determine the depth of the bottom. A transmitter, a receiver that picks up the reflected echo, electronic timing and amplification equipment, and an indicator or graphic recorder are located on the ship that can travel where needed to measure the depth of the ocean.
- These all involve a line going to the bottom of the
ocean with a device to physically obtain a sample. There
are many different types of dredges and they often are
employed to remove material from the ocean floor, for
example to deepen a harbour. When the dredge is employed to
gather data it would have a bucket or a grab in which to
collect material. Dredges collect bottom-dwelling
organisms, cutting a few centimetres into the bottom, and
extending less than half a meter above the bottom. The
material is then enclosed in a container so it can be
brought to the surface.
- Core sampling can be done in rock on the ocean floor
but is more often done in sediments. Drilling is done to
recover the core and there should be as little disturbance
as possible to the material. Core samples are taken from
ocean floors for purposes such as finding out about
previous climate or finding what organisms came to rest in
the sediment or lived in the sediment. Minerals found in
the core can be analysed. Core samples can be stored to be
analysed at a later date.
- Fish and plankton nets are used to collect fish or plankton, depending on the size of the mesh. A net called a neuston net is designed to collect fish just below the surface of the ocean. Plankton nets look something like a wind sock and will collect phytoplankton with a very fine mesh and zooplankton with a slightly larger mesh. Nets for collecting deep water fish can be deployed from a submersible.
- These have been in use since the 1950s and the original
ones consisted of a temperature sensor, a weight and a
piece of wire that holds the temperature sensor and
connects it to the ship that is taking the temperature
readings. They were designed to take temperatures of the
ocean at different depths up to about 500 metres while the
ship is moving. The operator would collect temperature
versus depth readings.
- In the 1970s expendable bathythermographs (XBT) were developed and these went to greater depths but are not recovered and sink to the bottom of the ocean. They measure temperature versus depth using a thermistor on a free-falling streamlined weight. The thermistor is connected to an ohm-meter on the ship by a thin copper wire that is spooled out from the sinking weight and from the moving ship. They reach to depths of 200m to 1830m depending on the model.
- Magnetometers are used to measure anomalies in the earth’s magnetic field. These can be due to local geologic features or objects in the area left behind by people, for example shipwrecks. Underwater magnetometers are usually towed behind a ship. Proton magnetometers operate on the principle that the protons in all atoms are spinning on an axis aligned with the magnetic field. Ordinarily, protons tend to line up with the earth's magnetic field. When subjected to an artificially-induced magnetic field, the protons will align themselves with the new field. When this new field is interrupted, the protons return to their original alignment with the earth's magnetic field. As they change their alignment, the spinning protons wobble as they slow down, much as a spinning top does as it slows down. The frequency at which the protons wobble is directly proportional to the strength of the earth's magnetic field.
- Read over what you have written about the two
technologies that you have described. Consider the evidence
they have provided to you about the oceans. Different
technologies have different functions so the one you choose
will depend on what information is required.
- Make a judgement about the value of the technologies you chose. Is one clearly better than the other or are they both equally valuable for what they achieve?
Extra information An echo sounding system is not new technology and was first used before
World War I. They were then used to detect submarines during World War
II. Echo sounders were continually improved until the early 1960s, when
a new technique of Sonar Array Survey System (SASS) was developed. This
system has recently been used to map more detailed representations of
the seafloor. It employs an array of sound transducers across the hull
of the survey vessel which radiate sound in a swathe, thereby allowing
a wide region of the seafloor to be mapped. This type of swathe-mapping
technology is now the way seafloor mapping is done. Another sonar instrument
uses a torpedo-shaped object to measure the strength of sound signals,
rather than the elapsed time of the returning signals, and covers larger
areas of the ocean floor. |
Dredges, Grabs and Core Samples
Fish and Plankton Nets
Bathythermographs
Magnetometers
evaluate the role of the oceanographic technologies studied in increasing knowledge and understanding about the oceans
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