chemical and physical features of seawater biography/3129/overview#tab-videos/05401_00
TRANSCRIPT
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Chapter 3Chemical and Physical Features of Seawater
http://channel.nationalgeographic.com/series/earth-the-biography/3129/Overview#tab-Videos/05401_00
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Properties of WaterLow Density of IceTemperature ModerationDissolves SubstancesCohesion and Adhesion*
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Low Density of Ice
Seawater Fresh waterColder = denser until
frozenCold water sinks
Colder = denser only to 4°C
Below 4°C = less dense
As temperature rises, hydrogen bonds break and evaporate
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Heat and WaterIn ice, hydrogen bonds
must be broken before molecules can move aroundNo hydrogen bonds =
melt at -90°C (-130F)Latent heat of melting:
the amount of heat required to meltHigher than any
common substance
Heat capacity: amount of heat needed to raise temperature by a certain amount
Latent heat of evaporation: the amount of heat required to evaporate
Evaporative cooling: fastest molecules leave liquid
*Water does not change temp easily.
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Water as a SolventUniversal solventDissolves salts wellSalt ions are
attracted to polar water molecules
Ability to transport minerals easily
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Seawater Substances come
from various sourcesWeathering:
chemical breakdown from rocks into rivers
Hydrothermal vents: minerals from Earth’s interior
Volcanoes: gases released into atmosphere and then into water as precipitation
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Seawater Salt CompositionOnly 6 ions compose
over 99% of solids dissolved in seawater
85% = Sodium and Chlorine
Salinity: total amount of salt dissolved in seawater
# grams left when 1,000g evaporatedpsu = practical salinity
units
Average = 35 0/00Open ocean =33 to
37Red Sea = 40 0/00Baltic Sea surface =
7 0/00
http://www.youtube.com/watch?v=jvd7uByNRRY
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Composition of SeawaterRule of constant proportions: relative
amounts of the various ions ins seawater are always the sameSalinity can change
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Salinity, Temperature, DensitySaltier/colder=
denserSalt water freezes at
lower temps than fresh
Density is controlled more by temperatureTemp varies
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Dissolved GasesOxygen
0 – 8 mL dissolved per L of seawaterAvg= 4-6 ml/lAir = 210 mL
Carbon dioxide80% of dis gases
NitrogenGases dissolve better in cold water
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TransparencySunlight needs to
penetrateClear water most
transparent to BLUEMost colors get
filtered out
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PressureLand = 1 atmosphere
(14.7 psi)WaterEach 10m of depth =1
ATMPressure increase =
gases compressAir bladders shrink
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“The Bends”: Decompression Sickness
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Ocean Circulation
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Surface CirculationMost intense ocean
currents are near the surface
Driven by the windInfluenced by the
Coriolis Effect
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Coriolis EffectAnything that moves
over the earth’s surface tends to turn instead of moving in a straight lineEarth is round and
rotating
Important for wind and ocean currents
Northern hemisphere = deflects to the right
Southern = left
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Wind PatternsDriven by heat
energy from the sunEquator: heated air
is less dense and rises
Air gets sucked in areas to replace rising air = wind
Trade winds: near equatorBlow west
Westerlies: middle latitudesBlow east
Polar easterlies: high latitudesBlow west
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Surface Currents
Driven by windMoves in a 45° angleEkman Spiral:
Top layer pushes on bottom Moves at a 45° angle againEach layer looses speed
Ekman Layer: layer affected by windWater moves at a 90° angle from wind
http://www.oscar.noaa.gov/
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Movement of Warm CurrentsEquitorial currents: move parallel to equator
Result of trade winds moved toward equatorCreate gyres: circular systems of current
Warm water moves away from equator; cooler water moves toward it
El Niño: large-scale fluctuation
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Currents Affect Surface TempEastern coasts are usually warmerWestern = cooler
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Layers of the OceanDensest water sinks,
least dense toward the surfaceStratified : layers
Surface layer100 to 200m thickMixed layer: wind, waves,
currentsThermocline: sudden
changes in tempIntermediate Layer
1,000 to 1,500mMain ThermoclineOnly open ocean
Deep and Bottom LayersBelow 1,500m (5,000 ft)Less than 4°C
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Thermohaline CirculationForm of circulation driven
by changes in densityDetermined by temp and
salinityCirculation over great
distances
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The Great Ocean Conveyor Global thermohaline
circulationRise and fall of
water throughout oceans
4,000 yearsCritical in regulating
climateBrings oxygen to
deep sea
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Waves and Tides
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Waves
Caused by windCrest: highest partTrough: lowest partHeight = distance between wave and troughWavelength: distance between wavesPeriod: time it takes for a wave to go by at one
point
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Wave Movement
Water particles move in circles
Not transportedFetch: span of open water over which the wind blows
Contributes to wave sizeSwells: smoothly rounded crests
waves move away faster than the wind is blowing
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SurfSurf: waves fall forward and break
Happens as the water becomes shallowerWaves behind catch up
Rogue waves: crests of two waves collide
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TidesRising and falling of
sea surfaceExpose/submerge
shore lifeDrive circulation of
bays and estuariesTrigger spawning
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Cause of Tides Gravitational pull of moon and sunMoon’s pull is
strongest on the closest side of the earth
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Daily Tides2 High and 2 Low
tides per dayBulges are on
opposite sides of the earth at one point in the day
Full tidal cycle is 24 Hours and 50 minutes
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Monthly TidesSun’s affect on tides is
only ½ of moon’sSpring Tides: Tidal range
increasesFull and new moons: sun
and moon are in line and their affects add together
Nothing to do with season
Neap tides: tidal range is smallFirst and 3rd quarters
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Variance on EarthNot all places are the sameSemidiurnal tides: 2 high and 2
low tides a dayEast coast, most of Europe and
AfricaMixed Semidiurnal: higher 2nd tide
of the day West coast
Diurnal: 1 high and 1 low tide per dayUncommonAntarctica, parts of Gulf of Mexico,
Caribbean, Pacific