Ocean Chemistry Unit 5
Ocean Chemistry • 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.
Focus • 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?
Properties of Water • H20 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
Focus • 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.
Seawater • 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, SO43-, and HCO3- • Elements <1 ppm are called trace elements
Focus • 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.
Sources of Ocean Salts • Weathering • running water dissolves crustal rock • Excess volatiles • hydrothermal vents (underwater volcanoes) on the ocean floor leak chemicals (C02,Cl, S, H, F, N) into the water
Chemical Equilibrium • 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
Focus • 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?
Water and Heat • 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.
Focus • 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?
Colligative Properties of Seawater • 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 • 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 • Osmotic Pressure • O.P. of organisms increases with increasing salinity (organisms lose more water when salinity is higher)
Focus • 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 effected by salinity?
Water Density • Density of water is a function of salinity and temperature. • Seawater density increases with increasing salinity, increasing pressure, and decreasing temperature.
Water Density • 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/cm3 • Density of liquid water is .999 g/cm3. • 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 • 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
Focus • 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.
Pycnocline • 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.
Focus • 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?
Dissolved Gases • 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 O2 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 marine plants- low at surface
Focus • 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?
pH • 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) Pure water Seawater 7.8
Focus • 26. Explain how pH works and in specific, the pH of the ocean. The End