Post on 01-Jan-2016
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Chemical Properties of Sea Water• polar: unequal sharing of electrons• hydrogen bonding: intermolecular dipole-dipole
interaction between H2O molecules• cohesion: sticking of H2O molecules to each other
resulting from hydrogen bonding; causes surface tension• adhesion: sticking of H2O molecules to other polar
materials• capillarity: movement of water up a small tube• latent heat: energy stored in water that doesn’t change
it’s temperature
Acidity/Alkalinity
• ocean: pH 7.5 to 8.5 due to carbonate (CO3-2)
from dissociation of calcium carbonate• freshwater: pH 6.5 to 7.5 due to carbonic acid
(H2CO3)
• bicarbonate buffering, resistance to pH change– H2O + CO2 H2CO3 (carbonic acid=weak acid)
– H2CO3 H+ + HCO3- (bicarbonate=buffer)
– CaCO3 Ca+2 + CO3-2 (carbonate=base)
Temperature
• depth dependent• thermocline: rapid
change in temperature around a certain depth; more defined near equator; less prominent at poles
• isotherm: line of constant temperature
Salinity
• isohaline: line of constant salinity• residence time: average time a molecule spends in
a certain reservoir• salinometers: determine salinity through
conductivity• halocline: rapid change in salinity• constancy of composition: major ion constituents
exist in constant proportions• water is the “universal solvent”• ocean salinity: 35ppt, brackish: 17ppt, brine: >50ppt• saltiest sea: Dead Sea
Salinity (continued)• Long-term sources:
– hydrothermal vents & volcanoes– weathering of rocks
• cation: positively charged ion• anion: negatively charged ion• salinity effected by:
– precipitation, evaporation– freezing, thawing– river input
• Top six constituents– chlorine (Cl-) 55%– sodium (Na+) 31%– sulfate (SO4
-2) 8%– magnesium (Mg+2) 4%– calcium (Ca+2) 1%– potassium (K+) 1%
Desalination
1. reverse osmosis
2. freezing & thawing
3. ion exchange
4. distillation (evaporation & condensation)
Density
• pycnocline: rapid change in density• freshwater most dense at 4 °C, saltwater most
dense just before freezing• saltwater freezes at -2 °C (freezing point
depression)• density affected by:
– temperature– salinity– depth, pressure: minimally
• isopycnal: surface of constant density
Pressure and Gases
• rises by 1 atm (14.7 psi, 101.3 kPa) for every 10 m (33 ft) depth
• absolute pressure at 20 m is 3 atm
• gauge pressure at 20 m is 2 atm
• isobar: line of constant pressure
Dissolved Gases
• Henry’s Law: more gas can be dissolved under high pressure
• more gas is dissolved in deep, cold water
• oxygen minimum zone: depth depends on productivity and aerobic respiration
• atmospheric gases resemble ocean’s due to mixing
Calcium Carbonate (CaCO3)• used in shells, compound of limestone and
calcite, base of coral reef• sources and sinks
– chemical precipitation, dissolution– weathering of limestone and calcite– organisms
• solubility increased by:– greater depths– higher acidity (lower pH)
• carbonate compensation depth (CCD): dissolution rate of CaCO3 equals supply rate
Nutrients• eutrophication: excessive
addition of nutrients
• oligotrophication: excessive removal of nutrients
• iron is the limiting nutrient for most algae
South Atlantic phytoplankton bloom
Heat Transfer
• conduction: molecules speed each other up by physically bumping
• convection: carried by movement of fluid
• radiation: electromagnetic radiation is absorbed and raises temperature
• heat is conducted faster in water than in air, so divers can get cold faster
Sound
• in water, speed of sound = ~1500 m/s (3500 mph), 5x speed in air
• speed changes with density• sound travels farther in water than light, so
it is good for cetacean communication• SOFAR (sound fixing and ranging)
channel: sound travels slower around 1000 m, and can go farther; sound gets stuck in this channel
Light• penetration
– long wavelengths (red) absorbed first– mid-range wavelengths (green, blue) go farthest
• attenuation: decrease in light intensity due to absorption and scattering by suspended particles
• turbidity increases attenuation• index of refraction (n) = 1.33
Other• conservative property: mostly affected by mixing and
diffusion (ex: salinity)• non-conservative property: affected mostly by
processes other than mixing and diffusion (ex: dissolved oxygen relating to productivity)
• temperature-salinity diagram: unique to different bodies of water; shows lines of constant density in sigma units