1. Water Properties

2. Molecular arrangement of water
The shape of the water molecule gives it special properties that affect marine organisms.
Viscosity is the resistance to flow: it provides buoyancy for plankton while increasing the energy used by nekton to swim.
Surface tension is the attraction of surface water molecules.
Water is the universal solvent. 2

3. Polarity
Because of the angles of its chemical bonds, the oxygen atom is on one end of the molecule and the hydrogen atoms are on the other.
With 8 protons in its nucleus, an oxygen atom has a much stronger attraction for electrons than does a hydrogen atom with its single proton.

4. Polarity
There is a greater probability of finding the shared electrons in water close to its oxygen atom than near its hydrogen atoms.
As a result, the oxygen end of the molecule has a slight negative charge and the hydrogen end of the molecule has a slight positive charge.

5. Hydrogen Bonding
Because of their partial positive and negative charges, polar molecules such as water can attract each other.
The attraction between a hydrogen atom on one water molecule and the oxygen atom on another is known as a hydrogen bond.

6. Hydrogen Bonding
Water is able to form multiple hydrogen bonds, which account for many of its special properties.
Hydrogen bonds are not as strong as covalent or ionic bonds, and they can form in other compounds besides water.

7. Heat Capacity
Because of the multiple hydrogen bonds between water molecules
Large amount of heat energy required to cause those molecules to move faster and raise the temperature of the water.
Large bodies of water, such as oceans and lakes, can absorb large amounts of heat with only small changes in temperature. This protects organisms living within from drastic changes in temperature.

8. Phase Change
Reversible physical change that occurs when a substance changes from one state of matter to another
Melting – solid to liquid
Freezing – liquid to solid
Vaporization – liquid to gas
Condensation – gas to liquid
Sublimation – solid to gas
Deposition – gas to solid

9. Temperature & Energy
The temperature of a substance DOES NOT change during a phase change!!
Energy is used to change molecule position

10. Sea Surface Temperatures10

11. Temperature The most important limiting factors:
Changes can alter many other parameters (thermal pollution is a big problem)
Surface water that is heated by the sun goes through seasonal changes.
The Thermocline is a narrow band of water that separates warm surface water from cool bottom water
Cold water holds more oxygen than warm water. 11

12. Salinity
The amount of dissolved solids in water includes ions of chloride, sodium, sulfate, magnesium, calcium and potassium.
Measured using a hydrometer to calculate specific gravity, or by conductivity. Units would be measured in ppt.
Surface salinity is greatly influenced by temperature.
High temps cause increased evaporation rates and increased salinity. 12

13. Salt Water Higher Boiling Point Lower freezing Point
Salt interacts with water to make it less “organized”

14. pH – In sea water, pH is between 7.5 –8.5
Closely associated w/ dissolved CO2
CO2 is a reactant in photosynthesis and a product of respiration.
Dissolves easily in sea water and is stored in marine shells and sediments. 14

15. pH cont. Both reactions change the pH of the water.
pH is expressed on a scale from 1-14. 15

16. The pH Scale 16

17. pH Cont.
A decrease in pH could dissolve the calcium carbonate in mollusk shells. 17

18. Density Freshwater density = 1.00g/cm3 Saltwater density = 1.03 g/cm3
Why higher?
Volume is the amount of space taken up by an object.
Density is the ratio of an object’s mass to its volume:
Affected by both temperature and salinity
800x’s as dense as air.
Density causes buoyancy

19. Buoyancy
The forces from pressure acting on the bottom of this golf ball are greater than those on the top.
This produces a net force— called the buoyant force— that acts upward on the ball.

20. Buoyancy
Buoyancy is the ability of a fluid to exert an upward force on an object placed in it.
Buoyancy results in the apparent loss of weight of an object in a fluid.
A submerged object pushes aside, or displaces, a volume of fluid equal to its own volume.
A floating object displaces a volume equal to the volume of the part of the object that is submerged.

21. Floating vs sinking
How can you determine if an object will float or sink in a fluid?
If an object is less dense than the fluid it is in, it will float.
If the object is more dense than the fluid it is in, it will sink.
Buoyant force
Weight

22. Forces again
Two forces act on every object in a fluid—weight and the buoyant force.
The force of gravity, equal to the object’s weight, acts downward on the object.
The buoyant force, equal to the weight of the volume of displaced fluid, acts upward on the object.

23. Density and Buoyancy Suspended
An object that has the same density as the fluid it is submerged in will be suspended (it will float at any level) in the fluid.
The buoyant force acting on the suspended object exactly equals the object’s weight.
Submarines and some fish are able to suspend themselves in water partly by adjusting their density.
Neutral Buoyancy = Preventing movement up or down

24. Floating
Floating
A solid piece of steel sinks in water. A heavy steel ship floats because of the shape of its hull.
The hull is shaped so that it displaces a large volume of water, creating a large buoyant force.

25. Density and Buoyancy
The weight and buoyant force determine if an object sinks or floats.
Buoyant force
Weight
Buoyant force
Weight
Buoyant force
Weight

26. Dense Fluids Objects also float more easily in dense fluids.
The denser the fluid is, the greater is the weight displaced. The greater displaced weight results in a greater buoyant force.
This is why it is easier for a person to float in very salty water. The dense salty water produces a larger buoyant force when displaced by the person's body.
Displace less water

27. Transmission of Light
Light in the sea comes from two sources: sun and organisms
A large portion of the electromagnetic radiation from sun (or moon) is reflected back into atmosphere -- so only the upper kilometers of the water column are illuminated 27

28. Seeing the Light
Light below the surface differs from that above in both quality and quantity because a major change occurs at the air-sea surface interface 
Combined consequences of reflection from the surface and refraction into it reduce the angular distribution of light to a narrow cone of solid angle 97° 
So a fish looking upward only sees the surface above water in that cone -- or window (called Snell's window) -- outside of the window is back- scattered light from deeper water 28

29. Light Penetration
Water absorption preferentially removes both long (red) and short (ultraviolet) wavelengths, rapidly resulting in near-monochromatic blue light, which is then reduced by 90% for every 70 m of depth 
In coastal waters material from plant decay can absorb additional short wavelengths, resulting in a greenish hue to the water
Turbidity allows green wavelengths to penetrate

30. Penetrating Light
Since water selectively absorbs the reds and violets, blue penetrates to the lower limits of the photic zone (autotrophs use red and blue wavelengths) before being absorbed
The intensity of light decreases with greater depth
Thus autotrophs are restricted to the illuminated upper surfaces of the ocean, called the photic zone and are unable to live in the dark lower portion of the ocean called the aphotic zone
Colors are seen differently in shallow vs. open ocean water: in shallow water there is a structural background of the shore or a reef which allows animals to hide in it; in open ocean, no refuge exists and the background is uniform

31. Light Cont.
Marine Plants (autotrophs) make their own food by photosynthesis. Heterotrophs can’t make food so they eat plants.
The cycle depends on light entering the water which may be absorbed or reflected.
About 65% of light energy is absorbed in the first 5 feet and can’t be used by autotrophs. 31

32. More Light
Red light is absorbed first in most marine environments. Many marine bottom dwelling animals are red. Why?
Blue is transmitted best
Light is inversely proportional to depth. As you descend, it gets darker.
The lighted layer is called the photic zone: about 10% of the ocean.
The dark layer is the aphotic zone. 32

34. Turbidity Turbidity is a measure of the suspended sediments.
More sediments results in less light penetration and poor visibility. Photosynthesis is reduced. 34

35. Turbidity cont.
Turbidity can be measured with a secchi disk as visibility.Divide the depth of the secchi line by the water’s depth.
Turbidity is lower in areas of high productivity. 35

36. Pressure Pressure at sea level is the weight of air (14.7 psi)
As you descend, pressure results from the weight of the water above you (hydrostatic pressure) as well as air pressure. 36

37. Pressure going down For every 33 feet = 1 atm of pressure
At 100 feet = 4 atm of pressure or ~58.8 psi
The pressure at the Mariana Trench is ~ 7 tons/in2
Increased pressure lowers water’s freezing point without affecting the volume.
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