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Water Molecule: H2O
Loosely depicted electrons “shells”
Atoms w/ complete electron shells do not form bonds
Atoms w/ unfilled “shells” from molecules to fill them
H2O molecule makes both H and O happy
Covalent bonds between atoms are due to sharing electrons = strong bonds
Water’s Polarity
E- are not evenly distributed
Negative E- spend more time near larger oxygen nucleus
How does polarity allow for hydrogen bonds?
Hydrogen bonds: electromagnetic attractive interaction between strongly polar molecules, where the electropositive H is attracted to the electronegative O
Thermal Properties of Water
Heat = total kinetic energy of molecules
Temps = average motion of molecules
Molecule motion increase = temp increases
Heat Capacity
Ratio of the amount of energy absorbed to the associated temp rise.
Measured in joules/ kelvin or C=Q/deltaT
Sticky H bonds in water
Requires a lot of energy to break
Result: water has high specific heat capacity and can store huge amounts of heat (energy) wo/ changing temperature
Heat Capacity of Air
low heat capacity = rapid change in temp w/ energy input
Heat Capacity of Water
high heat capacity = slow change in temperature with energy input
Consequences of Water’s High Heat Capacity
buffers ocean organisms from atmospheric temp changes.
buffers coastal land from large temperature changes
Three Phases of Water
Water is the only substance on earth naturally found as gas, liquid, and solid states
Latent Heat
Energy released or absorbed by a body during a constant-temp process
High Latent Heat
Even more energy required to freeze or vaporize water
Why is it Critical That Ice Floats
Ice floats, the water below is insulated and does not freeze
If ice formed on the bottom of the oceans, life as we know if would not be possible on Earth because all bodies of water would eventually freeze solid
Water Density and Temperature
Cooling slows water molecule movement, so more water molecules can be packed into a given space until it freezes, molecules from rigid lattice, making ice less dense than cold water
Salt
Anything made of two ions - one positive, one negative “stuck” together by electrostatic attraction (ionic interactions)
Salt effects water’s density
What Salts are in Seawater?
Salinity = the total amount of salts + gases dissolved in water
g Salts/ g Salts + g Water X 1000
Seawater Salinity
Dead sea 340% salt
Average Ocean 35% salt
Estuary 18% salt
Drinking water <0.1% salt
Temperature, Salinity, and Pressure > Density
Decrease temp » Increase density
Increase salinity » Increase density
Increase pressure » Increase density
Thermocline
Rapid change in temp
Halocline
Rapid change in salinity
Pycnocline
Rapid change in density
Light Attenuation with Depth
Light does not travel well through water, light energy decreases exponentially with depth
Euphotic Zone: 100-1% surface light
Enough for photosynthesis
Dysphotic Zone: 1-0% surface light
Enough for some animals to see
Not enough for photosynthesis
Aphotic Zone: 0%
No light from the surface
Seawater Strongly Affects Light
Affects intensity and spectral composition
Not only is the ambient light photo darker but the colors are very different
Light Absorption in Water
Red light and violet light preferentially absorbed
Blue light is scattered so H2O minimum absorption = 460nm
Absorption spectrum depends on water composition
Algal Pigments are Adapted to Habitat
Different marine algae have different suites of pigment to optimize light their given habitat (costal vs open ocean, shallow vs deep)
