1. Polar molecule - a molecule (such as water) with an uneven distribution of charge

   • The oxygen end of a water molecule has a partial negative charge

   • Hydrogen end has a partial positive charge

2. Hydrogen bonds - the reason water molecules “stick” together.

   • There are hydrogen bonds between the molecules

     • Opposite charges between oxygen and hydrogen cause attraction

       • Ex: Magnets

3. Cohesion - the attraction of molecules for other molecules of the same kind

4. Surface tension - results from greater attraction of water molecules to each other (due to cohesion) than to molecules in the air (due to adhesion)

Aquatic Organisms

• Because ice is less dense than water, it acts as an insulating blanket that helps keep the water below from rapidly cooling off

Heat Capacity

• Water has a high heat capacity — it absorbs a lot of heat before it begins to get hot

• Water must also lose a lot of heat before it freezes

• This is good for marine organisms because they are not subjected to rapid or drastic changes in temperature

Solids in Seawater

• Solids are dissolved in water by

  • Chemical weathering of rocks on land

  • Earth’s interior

    1. Hydrothermal vents

    2. Released into the atmosphere from volcanoes (enter as rain or snow)

5. Salinity - is defined as the total amount of salt dissolved in seawater

   • Average salinity of the ocean is 35 ppt (parts per thousand) or 3.5%

   • The composition of the ions in seawater can be determined by analyzing the salts left after evaporating the water

   • Most abundant ions in seawater are chlorine followed by sodium

• Rule of Constant proportions

  • Organisms are not only affected by the total amount of salt but also the ratio of each kind of salt

6. Rule of constant proportions - the relative amounts of each of the various ions in seawater is always constant

   • Although organisms may be exposed to changes in total salinity, they don’t have to deal with changes in the ratios of various ions.

7. Evaporation - the process that changes liquid water to gaseous water (water vapor)

   • Salt does not evaporate but stays in solution

8. Freezing - the process that causes a substance to change from a liquid to a solid

   • Salt does not freeze with the water

9. Precipitation - water released from clouds in the form of rain

   • Also added by the melting of glaciers and ice

   • Less salinity areas have high precipitation

Highest Salinities

• Latitudes where evaporation is greater than precipitation

• Partially enclosed

Lowest Salinities

• Latitudes that get greater rainfall (precipitation)

• Near coasts where there is freshwater river runoff

Salinity and Temperature

• Ocean temperature varies between -2 degrees Celsius and 30 degrees Celsius

• Temperatures below 0 degrees Celsius are possible because saltwater freezes at a lower temperature than freshwater

• Water gets denser as it gets colder

• Water also gets denser as it gets saltier

Dissolved Gases

• Three most important gases in the ocean

  1. Oxygen

  2. Carbon dioxide

  3. Nitrogen

• All are found in the atmosphere and dissolve into or are released from the surface of the ocean (Gas exchange)

• Dissolved gases in water are also influenced by organisms (respiration, photosynthesis, decomposition)

• Gases dissolve better in cold water than warm water

• Therefore, cold water holds more oxygen than warm water. (Note: thermal pollution decreases oxygen levels)

Transparency of Water

• Ability of light to penetrate the ocean

• Depends on suspended/dissolved material in the water

• Microorganisms (ex: plankton) and sediments reduce transparency

• Coastal waters are often more clouded because material is brought in by the rivers

Transparency

• Different colors of light penetrate to different depths in the ocean

  • Most transparent to blue (blue light penetrates the farthest).

  • Red is the first color absorbed by the water or filtered out

  • Before long, only blue light remains

Under Pressure

• Pressure changes dramatically with depth in the ocean

• On land (sea level), we are under 1 atmosphere of pressure (or 14.7 pounds/square inch, psi)

• This is the weight of all the air above us

• Every ten meters of depth is another atmosphere (ATM) of pressure

Effect of pressure on Organisms

Under the sea, organisms are under pressure from all the water above and all the atmosphere above.

• As pressure increases, gases are compressed

  • Gas filled organs (air bladders and lungs) shrink

  • Our lungs would collapse under the pressure

  • This limits the depth range of many organisms