Water and Ocean Water and Ocean StructureStructure

Chapter 6Chapter 6

The Water MoleculeThe Water Molecule

• MoleculeMolecule– Group of atoms held together by Group of atoms held together by

chemical bondschemical bonds

•Covalent bondsCovalent bonds– Pairs of electrons are sharedPairs of electrons are shared– Sharing leads to an unequal Sharing leads to an unequal

distribution of chargedistribution of charge104.5104.5oo bond angle (H-O-H) bond angle (H-O-H)

The Water MoleculeThe Water Molecule• Having a “+ end” and a “- Having a “+ end” and a “-

end” makes water a polar end” makes water a polar moleculemolecule– Makes water able to separate Makes water able to separate

molecules held together by molecules held together by opposite electrical chargesopposite electrical charges•SaltsSalts

– Water = universal Water = universal solventsolvent

– Makes water able to attract Makes water able to attract similar moleculessimilar molecules•Forms H bond with nearby Forms H bond with nearby

water moleculeswater molecules

The Water MoleculeThe Water Molecule

• CohesionCohesion– The sticking together of The sticking together of

individual water moleculesindividual water molecules

•Surface tensionSurface tension

• AdhesionAdhesion– The sticking of water to The sticking of water to

solidssolids

•Makes thing wetMakes thing wet

• Both lead to capillary Both lead to capillary actionaction

Water and HeatWater and Heat• HeatHeat

– The energy produced by the random The energy produced by the random vibration of atoms or moleculesvibration of atoms or molecules•How many How many andand how rapidly how rapidly

• TemperatureTemperature– An object’s response to and input (or An object’s response to and input (or

removal) of heatremoval) of heat•Different substances = different Different substances = different

responsesresponses•How rapidlyHow rapidly

• More heat energy – Hot bath or More heat energy – Hot bath or candle flame?candle flame?

• DegreesDegrees– Temperature measurementTemperature measurement

•Celsius vs. Fahrenheit Celsius vs. Fahrenheit – 11ooC = 1.8C = 1.8ooFF

•ConversionsConversions– ooC C ooFF

ooF = F = ooC x (9/5) + 32C x (9/5) + 32ooF = 20F = 20ooC x (9/5) + 32 = 68C x (9/5) + 32 = 68ooFF

– ooF F ooCCooC = (C = (ooF – 32) x 5/9F – 32) x 5/9ooC = (60C = (60ooF – 32) x 5/9 = 15.6F – 32) x 5/9 = 15.6ooCC

Water and HeatWater and Heat• Heat CapacityHeat Capacity

– A measure of the heat required to raise the A measure of the heat required to raise the temperature of 1g of a substance by 1temperature of 1g of a substance by 1ooCC

•Calories per gramCalories per gram– CalorieCalorie

The amount of heat required to raise The amount of heat required to raise the temperature of 1g of water by the temperature of 1g of water by 11ooCC

– Heat capacity of water one of the Heat capacity of water one of the highesthighest of of all substancesall substances

•Can absorb (or release) large amounts of Can absorb (or release) large amounts of heat without large changes in temperatureheat without large changes in temperature

Water Temp. and DensityWater Temp. and Density

• Density = mass per unit volumeDensity = mass per unit volume– Most substances become denser as they Most substances become denser as they

get colderget colder

•Water becomes more dense as heat is Water becomes more dense as heat is removed…removed…

Water Temp. and DensityWater Temp. and Density

……until it approaches its freezing pointuntil it approaches its freezing point

•Density quickly Density quickly decreasesdecreases as it turns as it turns from water to icefrom water to ice– FreezingFreezing

Bond angle changes from 104.5Bond angle changes from 104.5oo to 109to 109oo

Forms regular hexagonsForms regular hexagonsWater expands by ~9%Water expands by ~9%

Latent HeatsLatent Heats• Latent heat of fusionLatent heat of fusion

– Heat removed during freezing that does Heat removed during freezing that does not change the temperaturenot change the temperature•80 calories of heat per 1g of water at 80 calories of heat per 1g of water at

00ooC to form iceC to form ice

• Latent heat of vaporizationLatent heat of vaporization– Heat added during evaporation that Heat added during evaporation that

produces a change in state but does not produces a change in state but does not cause a change in temperaturecause a change in temperature•540 calories per 1g of water at 20540 calories per 1g of water at 20ooCC

– Highest on EarthHighest on Earth

Seawater vs. Pure WaterSeawater vs. Pure Water

• SeawaterSeawater– 96.5% pure water96.5% pure water– 3.5% dissolved solids and gasses3.5% dissolved solids and gasses

•Lower its latent heat by ~4%Lower its latent heat by ~4%

•Act as a natural antifreezeAct as a natural antifreeze– Salinity goes up Salinity goes up freezing point freezing point

goes downgoes downFreezing point of seawater = -Freezing point of seawater = -

1.91.9ooC (28.6C (28.6ooF)F)

Seawater vs. Pure WaterSeawater vs. Pure Water

• Both freezing and evaporating Both freezing and evaporating seawater leaves salt behindseawater leaves salt behind– Leftover dense water sinks to the Leftover dense water sinks to the

bottombottom

• Seawater evaporates more slowly Seawater evaporates more slowly than freshwaterthan freshwater– 3.3 cubic feet of the sea evaporates per 3.3 cubic feet of the sea evaporates per

yearyear

•Left over heat powers wind Left over heat powers wind waves, waves, storms, and currentsstorms, and currents

Global Thermostatic EffectsGlobal Thermostatic Effects

• Thermostatic propertiesThermostatic properties– Properties of water that act to moderate Properties of water that act to moderate

changes in temperaturechanges in temperature

•Thermal inertiaThermal inertia– Resisting temperature changes with Resisting temperature changes with

the input or loss of heatthe input or loss of heat– Temp differencesTemp differences

•Land – 250 Land – 250 ooFF

•Ocean – 61 Ocean – 61 ooFF

Effects of Water and Air Effects of Water and Air MovementMovement

• Why doesn’t the water at the equator Why doesn’t the water at the equator boil away or the oceans at the poles boil away or the oceans at the poles entirely freeze solid?entirely freeze solid?– Currents move heat in water/air from Currents move heat in water/air from

tropics to polestropics to poles

•Equalizes polar-tropical heat Equalizes polar-tropical heat imbalanceimbalance

Effects of Air and Water Effects of Air and Water MovementMovement

•Example – Gulf StreamExample – Gulf Stream– ““outgoing” water is 10outgoing” water is 10ooC warmer C warmer

than “incoming” waterthan “incoming” water10 million calories/meter10 million calories/meter33

Flow = 55 million meterFlow = 55 million meter33/second/second550 trillion calories moved 550 trillion calories moved

North/secondNorth/second– Energy used to evaporate ocean is Energy used to evaporate ocean is

released to make water vaporreleased to make water vapor•Usually at a distanceUsually at a distance

– Cools Cuba Cools Cuba warms Canada warms Canada

Density Structure of the Density Structure of the OceanOcean

• Liter of seawater – 2% to 3% more Liter of seawater – 2% to 3% more dense than pure waterdense than pure water– Density of seawater = 1.020 – 1.030 Density of seawater = 1.020 – 1.030

g/cmg/cm33

– Dissolved solids (“salt”)Dissolved solids (“salt”)

• Density goes up when the…Density goes up when the…– Temperature goes downTemperature goes down– Pressure goes upPressure goes up– Salinity (how salty) goes upSalinity (how salty) goes up

Density Structure of the Density Structure of the OceanOcean

• Density zonesDensity zones– Surface zone (mixed layer) (2%)Surface zone (mixed layer) (2%)

•Least denseLeast dense•Temp and salinity mostly constant Temp and salinity mostly constant

throughoutthroughout– Pycnocline (18%)Pycnocline (18%)

•More denseMore dense•Density increases with depthDensity increases with depth

– Deep zone (80%)Deep zone (80%)•Most dense (below 1,000m)Most dense (below 1,000m)•Little change in density with depthLittle change in density with depth

Density Structure of the Density Structure of the OceanOcean

• Temperature and stratificationTemperature and stratification– Pycnocline changes density so rapidly Pycnocline changes density so rapidly

due to temperature changedue to temperature change

•ThermoclineThermocline– Regional differences? Factors?Regional differences? Factors?– Tropical regions – deep thermoclineTropical regions – deep thermocline– Polar regions – no thermoclinePolar regions – no thermocline

Density Structure of the Density Structure of the OceanOcean

• Salinity and stratificationSalinity and stratification– Low salinity creates stratificationLow salinity creates stratification

•Wherever precipitation exceeds Wherever precipitation exceeds evaporationevaporation– Creates the haloclineCreates the halocline

Zone of rapid salinity increase with Zone of rapid salinity increase with depthdepth

• Thermocline (temp) + Halocline Thermocline (temp) + Halocline (salinity) = Pycnocline (density) (salinity) = Pycnocline (density) – Water massWater mass