Chapter 3Chemical and Physical Features of Seawater

http://channel.nationalgeographic.com/series/earth-the-biography/3129/Overview#tab-Videos/05401_00

Properties of WaterLow Density of IceTemperature ModerationDissolves SubstancesCohesion and Adhesion*

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

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.

Water as a SolventUniversal solventDissolves salts wellSalt ions are

attracted to polar water molecules

Ability to transport minerals easily

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

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

Composition of SeawaterRule of constant proportions: relative

amounts of the various ions ins seawater are always the sameSalinity can change

Salinity, Temperature, DensitySaltier/colder=

denserSalt water freezes at

lower temps than fresh

Density is controlled more by temperatureTemp varies

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

TransparencySunlight needs to

penetrateClear water most

transparent to BLUEMost colors get

filtered out

PressureLand = 1 atmosphere

(14.7 psi)WaterEach 10m of depth =1

ATMPressure increase =

gases compressAir bladders shrink

“The Bends”: Decompression Sickness

Ocean Circulation

Surface CirculationMost intense ocean

currents are near the surface

Driven by the windInfluenced by the

Coriolis Effect

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

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

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/

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

Currents Affect Surface TempEastern coasts are usually warmerWestern = cooler

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

Thermohaline CirculationForm of circulation driven

by changes in densityDetermined by temp and

salinityCirculation over great

distances

The Great Ocean Conveyor Global thermohaline

circulationRise and fall of

water throughout oceans

4,000 yearsCritical in regulating

climateBrings oxygen to

deep sea

Waves and Tides

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

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

SurfSurf: waves fall forward and break

Happens as the water becomes shallowerWaves behind catch up

Rogue waves: crests of two waves collide

TidesRising and falling of

sea surfaceExpose/submerge

shore lifeDrive circulation of

bays and estuariesTrigger spawning

Cause of Tides Gravitational pull of moon and sunMoon’s pull is

strongest on the closest side of the earth

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

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

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