1. Ocean Chemistry Unit 5

2.  The chemical properties of the ocean are important to understand because the marine environment supports the greatest abundance of life on earth.  This life is largely made up of the same chemicals that comprise the ocean—water and salts. Ocean Chemistry

3.  1. Why is it important to understand the chemistry of the ocean?  2. What is the chemical make-up of the life in the oceans? What is it similar to? Reflection

4.  H 2 0 is a compound of 2 hydrogen atoms and one oxygen atom in a fixed proportion.  Held together by covalent bonds  (sharing of e-)  Molecular shape is bent into a 105° angle  Electrically unbalanced because of the angle and thus considered polar because of the (+) and (-) end  H bonds form between water molecules and other charged substances due to the polarity.  This allows water to stick to itself, a process known as cohesion  Adhesion is when water H bonds to other materials  Universal solvent: it will dissolve almost anything Properties of Water

5.  3. What makes up a water molecule?  4. How is it bonded? Give details.  5. Discuss the polarity of water.  6. Write about its adhesive, cohesive and solvent properties. Reflection

6.  NaCl dissolves in water because of it’s polarity  97.2% of Earth’s surface water is marine  Seawater is 96.5% water and 3.5% dissolved substances (mostly salts)  Earth has 5.5 trillion tons of salt  Nearly every element found in the crust and atmosphere is also present in the ocean  Major constituents of seawater  H, O, Cl, Na, Mg, Ca, K, SO 4 3-, and HCO 3 -  Elements <1 ppm are called trace elements Seawater

7.  7. Use the previous slide to describe marine water (saltwater) in detail. Include in your description all of the properties and composition that is given. Reflection

8.  Weathering  running water dissolves crustal rock  Excess volatiles  hydrothermal vents (underwater volcanoes) on the ocean floor leak chemicals (C0 2,Cl, S, H, F, N) into the water Sources of Ocean Salts

9.  The ocean is in chemical equilibrium  For the most part, ions are added to the ocean at the same rate they are subtracted  Certain ions have longer residency times then others  Addition of salts from the mantle and weathering are balanced by the subtraction of minerals bound into sediments Chemical Equilibrium

10.  8. Where do the salts and other minerals in the ocean come from?  9. What is meant by equilibrium? How does the ocean maintain equilibrium? Reflection

11.  Heat is energy produced by random vibrations of atoms or molecules.  Four sources of heat in the ocean:  solar energy  radioactive decay  heat from Earth formation  artificial heat from humans  Temperature is an object’s response to input or removal of heat.  1°C = 1.8°F  O°C is freezing  100°C is boiling  About 1m (3.3 ft) evaporates from the surface of the ocean every year. Water and Heat

12.  10. Define heat.  11. What are four sources of heat in the ocean?  12. Define temperature and note the freezing and boiling points for water.  13. How much water evaporates from the ocean each year? Reflection

13.  Heat Capacity  heat required to raise 1 g of substance 1°C  Heat capacity of water is among the highest of all known substances.  Water can absorb (or release) large amounts of heat with little change in temp.  The heat capacity of seawater decreases with increasing salinity (saltwater is less able to hang on to heat) Colligative Properties of Seawater

14.  Salinity  total quantity of dissolved inorganic solids in water (NOT just salt!)  Salinity is usually 3.3-3.7% depending on evaporation, precipitation, and freshwater runoff  Proportion of Cl to salinity is constant:  Salinity in % = 1.81 x Cl %  As salinity increases, freezing point decreases  Gives seawater a natural “antifreeze” property (saltwater freezes at a lower temp than fw)  Salt water evaporates more slowly than fw (salt hangs onto water) Colligative Properties of Seawater

15.  Osmotic Pressure  O.P. of organisms increases with increasing salinity (organisms lose more water when salinity is higher) Colligative Properties of Seawater

16.  14. What are the 3 given colligative properties of seawater?  15. Describe, in detail, the heat capacity of water.  16. Describe, in detail, the salinity of sea water.  17. How is the osmotic pressure of organisms affected by salinity? Reflection

17.  Density of water is a function of salinity and temperature.  Seawater density increases with increasing salinity, increasing pressure, and decreasing temperature. Water Density

18.  Freezing & Density  During the transition from liquid to solid, water expands  This makes ice less dense than liquid water, and thus floats.  Density of ice is.917 g/cm 3  Density of liquid water is.999 g/cm 3.  Density of water increases as seawater freezes.  Ice crystals are pure water because they exclude the salt.  The left over cold, salty water is very dense. Water Density

19.  Ocean Layers  The ocean layers by density stratification.  Surface (mixing) zone  2%  least dense zone  Top of the sea can actually be fw  Pycnocline  18%  density increases with depth  Deep zone  80%  below 1000m, densest layer Water Density

20.  18. How does salinity and temperature affect the density of the ocean?  19. Describe in detail, the relationship of freezing temperatures and water.  20. Describe the result of density stratification and the three layers of the ocean associated with it. Reflection

21.  Thermocline + Halocline = Pycnocline  Halocline - the area where the salinity changes rapidly.  Thermocline - the layer that changes in temp rapidly.  Can range in temp from 30.5-37.5°F  Average temp of ocean being 38°F.  Water masses (having characteristic temp and salinity, density) get trapped at great depths.  The pycnocline isolates 80% of the ocean from the 20% circulating on the surface. Pycnocline

22.  21. What are the two layers that make up the pycnocline?  22. What is special about each of these two layers?  23. How does the pycnocline isolate 80% of the water in the ocean? Reflection

23. Gases dissolve most readily in cold seawater Plants and animals in the ocean require dissolved gases in order to survive  Nitrogen  48% of gas in ocean (atmosphere 78%)  living organisms require N to build proteins, but bottom dwelling bacteria must “fix” the N into a useable form for them  Oxygen  36% of gas in ocean (atmosphere has 100x more)  Primary source of O 2 in ocean is from plants  most of the oxygen is near the surface and diffuses into the atmosphere  Carbon dioxide  15% of gas in ocean (60x more in ocean than atmosphere)  used by phytoplankton- low at surface Dissolved Gases

24.  24. Where does gas most readily diffuse in the ocean?  25. What are three major gasses found in the ocean? In what quantity is each found? How are they each used in the ocean? Reflection

25.  Acidity (release of H+) and alkalinity (release of OH-) is measured by pH  The ocean contains buffers to prevent large swings in pH when acids or bases are introduced  pH scale 0-----------------------------7----------------------------14 acid neutral base (alkaline) pH Pure water Seawater 7.8

26.  26. Explain how pH works and in specific, the pH of the ocean. The End Reflection