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9.8 Oceanography: 3. Physical, chemical and biological environments

Extract from Earth and Environmental Science Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW.

[Edit: 28 July 09]

Prior learning: Stages 4 & 5 Science 5.7.3 iii)

Preliminary Course Planet Earth and its environment- a five thousand million year journey 8.2.2.

Background: This is a fascinating field with research currently being done in several oceans. New species are constantly being found and it is predicted there will be thousands more found, especially in the deep oceans.

process and analyse information that explains the origin of the water and salt in the world’s seas and oceans

• Use the information in the dot point below as well as information given to you by your teacher or other source such as a guest scientist or information obtained in magazines and journals. One way you could process the information would be to assess the reliability of information from different sources. This can be done by seeing if information from various sources agrees with the main ideas. Is it possible that more than one source could be correct even if they don’t correlate 100%? If you have a guest scientist discuss reliability with him or her.
  
  
• Analyse the information. This could be done by considering if the causes would lead to the effect observed.

outline the origin of salinity in the Earth’s seas and oceans

• Water is an effective solvent and a portion of the ocean’s salinity is due to rain, groundwater or moving surface water dissolving crustal rocks.
  
  
• The major contributing component of the ocean’s salinity though is the chloride ion Cl ^-1 which is produced by outgassing from ocean vents and from mid-ocean ridges.
  
  
• Volatiles from the mantle are released into oceans as molten material which is rapidly cooled when it comes in contact with ocean water and in the process ions become dissolved in the water.
  
  
• Suspended particles swept to the ocean from the land by onshore winds, and materials dissolved from sediments deposited on the ocean floor have also contributed.
  
  
• It is also worth noting that the ocean’s salinity appears to have been fairly constant for the last billion years.

process data from secondary sources to map and describe the range of temperatures and salinity levels in vertical and horizontal zones of the Pacific Ocean

• Process the data to show trends and patterns by organising the data according to vertical and horizontal zones of the Pacific Ocean. You could show temperature and salinity separately and then indicate if there are any connections.
  
  
• Some resources are listed below.

Located at the mouth of Resurrection Bay near Seward, Alaska, temperature and salinity versus depth profiles have been taken at oceanographic station GAK1 (Gulf of Alaska) since December, 1970. Institute of Marine Science, University of Alaska, Fairbanks, Alaska, USA

Mean monthly temperatures near Seward, Alaska from 0 to 250 metres. These graphs show the temperatures at the different months of the year for particular depths. Note that the temperature readings on the x axis vary for different months. N is the number of samples taken that month. Institute of Marine Science, University of Alaska, Fairbanks, Alaska, USA

This gives salinity at standard depths. Note that the salinity readings on the x axis vary for different months. N is the number of samples taken that month. Institute of Marine Science, University of Alaska, Fairbanks, USA

 

• The above web links give you values for temperature and salinity in vertical zones at a northern point of the Pacific Ocean. You will now have to find some values at different sites in the Pacific such as near Japan and the east coast of Australia.

explain examples of common processes that change the salinity and temperature of oceans and small enclosed seas

There are more examples than you need below but you can choose which examples you want to. Choose two examples that result in change of salinity and two for change in temperature.

1. Salinity

   Background information
   In salt water when evaporation occurs only the water molecules evaporate from the solution leaving an ever increasingly saltier (more concentrated)solution.

   • Salinity is increased by evaporation or by freezing of sea ice and is decreased as a result of rainfall, runoff, or the melting of ice
     
     
   • Evaporation resulting in increased salinity occurs mostly in oceans and seas in mid-latitudes with warm temperatures and low rainfall.
     
     
   • Salinity is generally reduced by river discharge and freshwater runoff from land. The vast amount of precipitation associated with tropical storms as they move across the ocean surface also decreases salinity.
     
     
   • In the colder waters that freeze and thaw, salinity generally increases during periods of ice formation and decreases during periods of ice melt.
     
     
   • Salinity can be changed by the vertical mixing and inflow of adjacent water, such as near the mouth of a large river.
     
     
   • Small enclosed seas may have low salinities. The Baltic Sea ranges in salinity from about 5 to 15 o/oo. The salinity of the Black Sea is less than 20 o/oo.
     
     
2. Temperature
   
   
   • The ocean, like the atmosphere, is heated by the Sun’s incoming radiation. Some of this heat is given up to the atmosphere, and some of it is retained. Because the sea retains a portion of this heat, the sea-surface temperature (SST) is normally higher than the air temperature. However whether the sea surface is warmer or colder than the air above it at any particular moment depends on the locality, the season of the year, the atmospheric circulation and the ocean currents.
     
     
   • The temperature of the ocean ranges from about –2°C to 30°C. Ocean water that is nearly surrounded by land may have higher temperatures, but the open sea, where the water is free to move about, hardly ever heats above 30°C. Here, the ocean currents distribute the heat and tend to equalize the temperature. Deep and bottom water temperatures are always low, varying between 5°C and 1°C.
     
     
   • SSTs change from day to night just like those of the atmosphere, but to a much lesser degree. The diurnal (daily) variation of SST in the open ocean is on the average only 0.2°C to 0.3°C. The greatest diurnal variation takes place in the tropics, with lesser variation at higher latitudes. The range of diurnal variation depends on the amount of cloudiness and the direction and speed of the wind.
     
     
   • The smallest seasonal temperature variation of surface water occurs in equatorial and polar regions. The largest seasonal temperature variation occurs in the mid-latitudes (±2° Celsius from the monthly mean). In areas where warm and cold currents meet, surface temperatures may differ by 4°C. The absolute maximum is about 32°C in the Red Sea and Persian Gulf in summer with an absolute minimum of about –2°C in the polar region during the winter.
     
     
   • The annual range of surface temperatures is much greater over the oceans of the Northern Hemisphere than those of the Southern Hemisphere. This wider range of temperatures appears to be associated with the character of the prevailing winds, particularly the cold winds blowing from the continents. On the other hand, the annual range of ocean temperatures in the Southern Hemisphere is most definitely related to the range of incoming solar radiation, because of the absence of large land masses south of 45°S. Here, the prevailing winds travel almost entirely over water. This causes a greater degree of consistency in the annual sea surface temperature patterns and a much smaller annual temperature range compared to the Northern Hemisphere.
     
     More information can be found at this site. Foundation of American Scientists , Space Policy Project, USA 1. The water planet.

relate the range of temperatures and salinities measured in selected areas of the Pacific Ocean to the distribution of specific species

The web site below has information on the north Pacific Ocean. Trends in sea-surface temperature, salinity and density. Ministry of Environment, British Colombia,Canada. This is quite a big file but you just need to look at the first few pages.

Fish located in cold regions

All animals in the ocean have a "thermal range"- the temperature range at which they can most efficiently grow, reproduce, and live. Many fish habitats are described in relation to water temperature. Capelin (an energy-dense forage fish in the Smelt family) are an example of how ocean temperatures affect fish distribution, and in turn, seabird distribution and health. Capelin favour cold water. During a time period when surface waters are very warm, capelin migrate into deeper, cooler waters. When capelin are deeper in the water-column, they are less available to surface-feeding seabirds and possibly harder to obtain for diving seabirds. The absence of this nutritious fish in seabird diets may have an effect on seabird breeding success.

In areas where deep ocean currents hit a shallow shelf on the ocean floor, all the cold, deep water is forced upwards as it makes it way over the shelf.  This action brings high concentrations of nutrients from the ocean floor to the surface waters, which power marine food webs and create an abundance of food for fish, seabirds, and marine mammals.  Typically, these areas of cold water upwelling are host to multitudes of seabirds and marine mammals. 

identify data sources, plan, choose equipment and perform a first-hand investigation to compare the solubility of common salts in water of different temperatures

• To do this investigation you should research which salts are present in the oceans. It isn’t essential to use these salts in your investigation but it would be more meaningful. You should also research the range of temperatures in the oceans from the deep ocean beds to the surface and from the equator to the poles. Identify books and electronic sources to find the data, then record the data in an appropriate way.
  
  
• Plan your investigation by deciding how many different salts to use, what salts to use and what temperatures to use. Consider what factors will be kept constant and how many different set ups you will need.
  
  
• When you have planned your investigation choose the equipment you will need. Make sure the school has everything you plan to use.
  
  
• Perform the investigation, using repetition if necessary and taking care to use whatever safe work practices are necessary. Record your results in a table or other appropriate format.
  
  
• Compare the solubility of the different salts at the different temperatures. Make sure that you keep the results for the different salts quite separate.

analyse information from the above investigation and from secondary sources to predict the difference in composition of hot and cold water in oceans in terms of salt concentrations

• From the results above, predict where more salty water would be found in the oceans. Use the secondary sources to check if the salts in the various parts of the oceans agree with your predictions. If they do not agree in all cases, consider what other factors may result in this discrepancy.

describe the attenuation of light with depth in oceanic waters, and the order in which the different wavelengths of light disappear with depth in oceans

• The shorter wavelengths of light are able to penetrate ocean waters to a greater depth than longer wavelengths of light. This means that blue and violet light will be transmitted to the greatest depths in our oceans while red, orange and yellow will be absorbed in the upper layers of the ocean.
  
  
• Red wavelengths will be absorbed within the upper 10 metres of ocean waters while orange and yellow will be absorbed within the first 100 metres.
  
  
• Only blue and some green wavelengths will extend beyond depths of 100 metres, however, even these will only be transmitted at low intensity.
  
  
• In the open ocean no sunlight penetrates ocean waters beyond a depth of 1000 metres.

A good diagram that shows different wavelengths of light at various depths in deep ocean and in coastal waters can be found at National Oceanic and Atmospheric Administration, U.S. Department of Commerce, USA .

A description with formulae of why different wave lengths of light penetrate to different depths 6.10 Light in the Ocean and Absorption of Light by Robert H Stewart, Department of Oceanography, Texas A&M University, 2006

discuss the implications of limited light for the distribution of marine plants in near-shore environments and photosynthetic plankton in the open oceans

• The distribution of marine organisms depends on the physical and chemical properties of seawater such as temperature, salinity, and dissolved nutrients, as well as on ocean currents which carry oxygen to subsurface waters and disperse nutrients, wastes, spores, eggs, larvae, and plankton. It also depends on penetration of light. Photosynthetic organisms (plants, algae, and cyanobacteria), the primary sources of food exist only in the photic, or euphotic, zone (to a depth of about 90 metres), where light is sufficient for photosynthesis.
  
  
• Since only about 2% of the ocean floor lies in the photic zone, photosynthetic organisms in the benthos are far less abundant than photosynthetic plankton (phytoplankton), which is distributed near the surface oceanwide. Very abundant phytoplankton include the diatoms and dinoflagellates. Heterotrophic plankton (zooplankton) include such protozoans as the foraminiferans; they are found at all depths but are more numerous near the surface. Bacteria are abundant in upper waters and in bottom deposits.

The Living Sea, Life Near the Surface, Museum of Science, Boston, Masachusetts, USA

perform a first-hand investigation to demonstrate the precipitation of salts from a cooling solution and solve problems to use this information to predict precipitation in naturally occurring bodies of water

• Discuss with your teacher how you will do this investigation. Decide which salts you will use, the amount of the salts and what temperature the water will be to start. You may decide to record the temperature when the salt begins to precipitate. It would be advisable to use sodium chloride as one of the salts as this is the most common salt in the oceans. Label the containers clearly and measure the salts carefully.
  
  
• Perform the investigation, recording results accurately. A good way would be in a table.
  
  
• Use the information you have gathered to predict precipitation in naturally occurring bodies of water.

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