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9.8 Oceanography: 6. Hydrothermal vents support unusual communities
Extract from Earth and Environmental Science Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW.
[Edit: 8 Aug 08]
Prior learning: Stage 6 Biology 8.2.1, Stage 6 Earth and Environmental Science 8.3.6
Background: Scientists searched for hydrothermal vents after finding evidence that they existed on land that had once been under the ocean. Several have now been found and they appear to be linked to mid ocean ridges.
solve problems, plan and perform an investigation to demonstrate the effect of surface area to volume ratio of solids on their cooling rate in water
- Solve the problem of what type of solid material to use
to best demonstrate the effect of surface area to volume ratio on the rate
of cooling. It would be best to have different sizes of the solid material
but use the same shape for each one to prevent having too many variables.
You may find that the science department already has small metal cubes of
different sizes. If not you may have to obtain appropriate solid material.
- Plan the investigation by considering how it can be done
to get the best results with valid and reliable data and information. Things
to be considered are:- what size containers to have the water in
- what temperature the water should be to start
- how to heat the solid material to have uniformity of starting temperature
- how to get the most accurate final temperature of the water.
- Perform the investigation while ensuring that you have minimised hazards by such things as wearing goggles while heating. Record your results in a suitable table. If the results are not clear cut you may need to repeat the investigation to ensure accurate results.
relate the heating of the water to the cooling of the newly formed crust
- As the cold water (approximately 2°C) circulates between the hot rocks it cools the rocks and at the same time the rocks heat the water.
describe the way in which seawater is heated by circulation within newly formed ocean crust
- At Mid-Ocean Ridges, where plates are moving apart, cracks and crevices are created in the ocean floor as new magma comes to the surface. Seawater seeps into these openings and is heated by the magma that lies beneath the Earth’s crust. As the water is heated, it rises and seeks a path back out into the ocean through an opening in the seafloor.
- As the vent water bursts out into the ocean, its temperature may be as high
as 400°C. Yet this water does not boil because it is under so much pressure
from the tremendous weight of the ocean above. This water contains many metals
and the site is called a black or white smoker, depending on which minerals
are extruded. A diagram of the water circulating can be seen.
Ocean
Explorer
, NOAA, USA
gather, process and present information from secondary sources that describes the processes and characteristics of hydrothermal vents and their unique biotic communities
- Gather information from the most up to date sources. These would be internet sites and current journals.
- Process the information by assessing the reliability of information from different sources.
- Present the information in the best manner to describe processes and characteristics of hydrothermal vents and their unique biotic communities.
Here is a website to start you in gathering information.
Biological studies; 2004
explain the ability of hydrothermal waters (brines) to scavenge elements from rocks
- Sea water flows into mid-ocean ridges and is heated to about 300-400°C from contact with partly solidified basalt rocks. The pressure is much greater at the depths of the ridge (2000 -5000 metres). The high temperatures and pressure cause minerals in the basalt to corrode and leach out into the water. Some metals that are released are copper, zinc and iron. This hot water containing the dissolved minerals is less dense than the surrounding water and so rises back up and mixes with ocean water at hydrothermal vents.
outline and describe the products and process of hydrothermal fluid discharge from deep-sea vents
- Hydrothermal fluid is altered sea water that has flowed into a mid-ocean ridge and interacted with the partly solidified rock, thereby changing physical and chemical characteristics of both the sea water and the rock.
- This hydrothermal fluid is then injected back into the ocean at hydrothermal vent fields and forms hydrothermal plumes. These plumes are often black or white with the colour due to mineral particles that precipitate rapidly as hot hydrothermal fluids (up to 340°C) mix with cold sea water (about 1-2°C) at or just below the vent opening.
- “Black smokers” consist of tiny metallic sulfide particles that precipitate out of the hot vent fluid as it mixes with the cold sea water.
- “White smokers” lack the metallic sulfide particles as any
that were present precipitated out below the vent opening, due to cooler temperatures.
Another chemical that contributes to white smokers is precipitated silica.
- Smokers will continue to rise in the ocean as long as they are less dense than the surrounding sea water. When the sea water has the same density as the smoker, the smoker will spread out horizontally.
perform an investigation to assess the relationship between the rate of hatching of brine shrimp to salt water concentration and temperature
Below is a possible investigation you could do.
- Obtain the brine shrimp eggs from a pet shop or other source.
- Research to find the normal temperature range in which brine shrimp hatch then decide what temperatures you will use in your investigation. (Don’t go more than two or three degrees on either side of the normal range as that could be considered cruelty to the brine shrimp.)
- Set up an investigation where the salt concentration remains constant and the temperature varies.
- Now set up an investigation where the temperature remains constant and the concentration varies. Make sure that the constant temperature is one that is favoured by the brine shrimp.
- Brine shrimp normally live in salt water of about 25 ppt (parts per thousand) so choose a range of concentrations that would be either side of their normal range.
- Do each investigation separately and record the results in two tables.
- Report your conclusions to the class.
describe examples of the unique bacteria and invertebrate species that live around hydrothermal vents
- The bacteria found in the water column coming from vent waters that have been described as ‘white snow’ and bacteria found on the rocky surfaces and on the surface of soft sediments get their energy from oxidising sulfide.
- One invertebrate that lives off these bacteria is a one metre long tube
worm that produces tubes about three metres long. These tube worms have no
obvious gut. Instead they have a specialized organ which has dense concentrations
of chambers that contain sulfide-oxidising bacteria. The animal, in turn,
can digest the bacteria and derive nutrition. Riftia, one of the
genera of tube worms, has a specialised haemoglobin, which binds to both sulfide
and to oxygen. The sulfide is transported to the specialised organ, where
it can be used by the symbiotic bacteria.
- Some bivalve molluscs have sulfur oxidizing bacteria as symbionts in their gills. Go to the website below to see some good photos of invertebrates found at the vents.
Hot Vents,
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