Chapter 3

Chapter 3chemical and physical features of seawater and the world ocean

The Unique Nature of Pure Water

The nature of waterAtom: The basic unit of matterThe smallest unit into which an element can be divided and still retain its properties

The nature of waterElement: A substance composed entirely of one type of atom

Molecule: Larger particle composed of two or more atoms chemically bonded together

The nature of waterHydrogen bonds: Weak bonds between polar moleculespolar molecule: a molecule with uneven distribution of charge The reason for waters unique properties

States of Water

States of WaterLiquid, Gas/Vapor, and Solid/CrystallineWater is the only substance that naturally occurs in all three forms

States of WaterLiquid -> Gas/Vapor Evaporation: The breaking of hydrogen bonds allows water to change from the liquid phase into the gaseous phase

States of WaterGas/Vapor -> LiquidCondensation: The formation of hydrogen bonds allows water molecules to come together and change from a gaseous phase to a liquid phase

States of WaterSolid -> Gas/VaporSublimation: The direct change in phase from a solid to a gas without a change in phase to a liquid in between

States of Water

States of WaterDensity = Mass/VolumeWater is the only known substance that is less dense as a solid than it is as a liquid

Heat and Water

Heat and WaterLatent heat of melting: The amount of heat required to melt a substancehighest among common substancesdue to hydrogen bonding

Heat and WaterHeat capacity: The amount of heat needed to raise a substances temperature by a given amountreflects how much heat a substance can storewater can absorb large amounts of heat without altering muchwhy water is used a common coolant ex. car engines

Heat and WaterLatent heat of evaporation: the amount of heat energy that is needed to evaporate a substancewater has a high latent heat of evaporationalso due to hydrogen bondingOnly fastest moving bonds are broken, allowing those molecules with more energy to evaporatelower energy molecules are left behind

Heat and WaterEvaporative cooling: the lower speed and therefore lower temperature of molecules remaining in the liquid phase after evaporation of the fastest moleculeshow evaporating sweat cools our skin

Water as a Solvent

Water as a Solvent Seawater is a solution: A mixture consisting of two parts a solvent and a solute which is evenly dissolved throughout the mixtureThe solute is the substance being dissolvedThe solvent is the substance that causes the dissolving

Water as a Solvent Often considered the Universal solventcan dissolve more things than any other natural substance

Water as a SolventSalts: Substances made up of particles with opposite chargesIons: Electrically charged particles that result from the loss or gain of an electronex. NaCl -> Na+ and Cl-

Water as a Solvent Dissociation: The separation of two oppositely charged particles in a substance into their individual ionsex. NaCl -> Na+ and Cl-

Seawater

SeawaterThe characteristics of seawater are due to two things:1. the nature of pure water2. the materials dissolved in the water

SeawaterSome of the material dissolved in seawater is the result of weathering of surrounding rocksWeathering: the physical or chemical breakdown of rocks

SeawaterSalinity: The total amount of salt dissolved in seawaterSalinity is usually defined as the amount of salt in grams that remains when 1,000 grams of seawater are evaporatedex. 35 g remains, 35 parts per 1000 or 35 pptthis is the average salinity of the ocean

SeawaterToday electronic equipment is used to measure salinityThe conductivity of seawater is a good indicator of its salinity - ions are charged

SeawaterOrganisms are affected by the concentration of salts and the types of salt found in particular seawaterex. Cl usually makes up 55.03% no matter what else is presentThis idea is called the rule of constant proportionsrelative amounts of the various ions in seawater are always the same

SeawaterWater is primarily removed by evaporation and less by freezingwhen seawater freezes, the ions are excluded from the iceice is almost pure waterWater is added by precipitation

Salinity, Temperature, Density

Salinity, Temperature, DensityTemperature and salinity effect waters densityit gets denser as it gets saltier, colder or bothTemperature in the open ocean varies from -2C 30C (28-86F)Temperature varies more than salinity

Salinity, Temperature, DensitySampling Bottles - measure temperature and salinityex. Niskin bottlesset up a rack with multiple bottles attached at different locations, measure many depths at once

Salinity, Temperature, Density

Salinity, Temperature, DensityWater column: a vertical shaft of water extending downward from the surface

Salinity, Temperature, DensityProfile: a plot that shows temperature, salinity, or any other characteristic of seawater at various depths in a water column

Salinity, Temperature, DensityToday electronic sensors are more commonly:CTDs: Conductivity-Temperature-Depth metersXBTs: Expendable Bathythermographs disposable, temperature measuresProblem: only measure one location at a time

Pressure

PressureOrganisms on land, at sea level, are under 1 atm of pressure, or the pressure of the atmosphere above them

PressureOrganisms in the water are under pressure from the atmosphere and the water above themEvery 10 ft of depth, 1 atm of pressure is added Problem for fish as well gas bladder

Buoyancy in Fish Bony Fish

Buoyancy in Fish Cartilaginous Fish

Dissolved Gases

Dissolved Gases3 most important for living organisms:1. Oxygen (O2)2. Carbon Dioxide (CO2)3. Nitrogen (N2)

Dissolved GasesGas exchange: the movement of gases between the atmosphere and the oceanGases dissolve better in cold waterOxygen is not very solubleThe amount of oxygen in the water is strongly affected by organisms through the processes of photosynthesis and respiration

Dissolved Gases

Dissolved GasesPhotosynthesis: 6CO2 + 6H2O + energy ---> C6H12O6 + 6O2

Respiration: C6H12O6 + 6O2 ---> 6CO2 + 6H2O + energy

Dissolved GasesCO2 is more easily dissolved, because it chemically reacts with watermakes up more than 80% of the dissolved gas in the oceanonly makes up 0.04% of airMakes the ocean critical to understanding the effects of human activities on the earths climate

Transparency

TransparencyWater is transparentallows sunlight to enterallows for photosynthesis to occur and life to continue

TransparencyNot all colors penetrate seawater equallyClear ocean water is most transparent to blue lightOther colors are absorbed more than blue, so as the depth increases only blue light can get through

TransparencyThe transparency of water is greatly affected by the material suspended in the water and the gases dissolved in the water

The Coriolis Effect

The Coriolis EffectThe Earth is round, therefore anything that moves over the surface tends to turn at least a little and does not move directly in a straight line.This bending is called the Coriolis Effectnamed after Gustave-Gaspard Coriolis who discovered it in 1835

The Coriolis EffectIn the Northern Hemisphere always turns to the rightIn the Southern Hemisphere always turns to the left

Wind Patterns

Wind Patternswinds in our atmosphere are driven by heat energy from the sunAs solar energy heats the Equator the air there becomes less dense and rises.Surrounding air gets sucked in to replace the risen air, creating windThe winds are bent due to the Coriolis effect

Wind PatternsThese winds near the Equator are called trade windsapproach the Equator at 45 anglesleast variable of the winds

Wind PatternsOther winds tend to be more variableMiddle latitudes - westerliesHigh latitudes - polar easterlies

Surface Currents

Surface CurrentsAll major surface currents of the ocean are driven by the wind

Surface CurrentsDue to the Coriolis effect, when the wind moves off, the water is pushed off at a 45 degree angleThe top layer of water then pushes on the next layer and again the Coriolis effect comes into playThe next layer moves more slowly and slightly towards the right of the top layer

Surface CurrentsEach successive layer in the water column follows this patternForms a pattern called the Ekman spiral after the Swedish oceanographer who discovered itekman spiral

Surface CurrentsAt a depth of a few 100 meters the effect of the wind is not felt at allThe upper part of the water column that is affected by the wind is called the Ekman layer

Surface CurrentsTaken as a whole the Ekman layer moves at 90 degrees from the wind direction in a process known as Ekman transportEquatorial currents move parallel to the equator

Surface CurrentsUnder the influence of the Coriolis effect the wind-driven surface currents combine into huge, more or less circular systems called gyresparticularly good at carrying heat due to waters high heat capacity

Surface Currents

Surface CurrentsLarge scale fluctuations in current patterns such as El Nino can dramatically affect weather around the world

Three-Layered Ocean

Three-Layered OceanSurface layer: 100-200m thickmixed by wind, waves and currentmixed layerheated by the sunThe warmer water floats in a shallow lens on top and there is a sharp transition to the cooler water below

Three-Layered OceanThe ocean is stratified, layered based on density

Three-Layered Ocean

Three Layered OceanThermocline: sudden changes in temperature over small depth intervalsWhen the weather cools, the thermocline breaks down by winds, waves and currents

Three Layered OceanIntermediate Layer: below the surface level1,000-1,500 m in depth (200 1,200/1,700 m from the surface)

main thermocline: a zone of transition between warm surface water and the cold water belowrarely breaks downfeature of the open ocean

Three-Layered Ocean

Three-Layered OceanDeep/Bottom Layer: Technically different, similar in being uniformly coldtypically less than 4C

Stability and Overturn

Stability and OverturnHow stable the water column is depends on the density difference between the layersA more stable water column has greater differences in density and requires more energy to mix the layers

Stability and OverturnSometimes the columns become unstable, meaning the surface water is more dense than the water belowthe surface water sinks causing downwellingthis water displaces and mixes with deeper water

Stability and OverturnProcess is known as overturn Scientists identify overturn by looking at straight line profilesWhen difference is only slight and mixing occurs, important for the productivity of temperate and polar waters

Stability and OverturnWhen large amounts of downwelling occurs, the salinity of that area is changedonce it has sunk, temperature and salinity do not change

Stability and OverturnFrom this point on the volume of water or water mass has a fingerprint - a characteristic combination of temperature and salinityThis is called Thermohaline circulation

Great Ocean Conveyor

Great Ocean ConveyorOverturn rarely reaches the ocean bottom, only in a few locations - Atlantic Ocean, south of Greenland and just north of Antarctica

Great Ocean ConveyorAfter sinking the water spreads through the Atlantic and to other ocean basinsWater eventually rises back to the surfaceflows back to the Atlantic where the cycle begins againThis is called the Great Ocean Conveyor

Great Ocean Conveyormixes the oceans about every 4,000 yearscritical to regulating the earths climatebrings dissolved oxygen to the deep sea

Great Ocean ConveyorIt is thought that alterations in the conveyor have produced rapid climate changes, even ice ages, in the past

Waves

WavesWind causes wavesWave: the undulation that forms as a disturbance moves along the surface of the water

WavesCrest: The highest part of the wave under a crest the water moves up and forwardTrough: The lowest part of the wave under a trough the water moves down and back

WavesBasically, water particles dont go anywhere when a wave goes past, they just move in a circleWaves carry energy, but not water

WavesThe size of a wave is usually expressed as the (amplitude) wave height: the vertical distance from trough to crest

WavesWavelength: the horizontal distance between crestsPeriod: the time the wave takes to move past a given point

WavesThe faster and longer the wind blows, the larger the waveThe size of the wave also depends on fetch: the span of open water over which the wind blows

WavesSeas: While the wind is blowing it pushes the wave crests up into sharp peaks and stretches out the troughs, these waves are called seas

WavesWaves move away from where they are generated slightly faster than the speed of the windOnce away from the wind they settle into swellssmoothly rounded crests and troughs

WavesAs waves approach the shoreline and reach shallow water, they begin to feel the bottom of the oceanThe bottom forces the water particles to move in elongated ellipses instead of circles, which slows the waveAs the waves behind catch up the waves get closer together, giving a shorter wavelength

Waves

WavesAs the waves behind catch up the waves get closer together, giving a shorter wavelengthThese waves pile up - higher and steeperEventually topple over or break - creating surf

WavesWhen two crests of two waves collide, they add together producing a higher waveThis is called Wave Reinforcement

WavesSometimes producing rogue waves that appear to rise up out of nowhere

WavesWhen a crest and a trough collide, they cancel each other outThis is called wave cancellation

Tides

TidesThe dominant force on near shore sea life.They alternately expose and submerge organisms on the shore, drive the circulation of bays and estuaries, trigger spawning and influence the lives of marine organisms in countless other ways

TidesThe tides are caused by the gravitational pull of the moon and sun/and the rotations of the sun, moon and earth

TidesThe earth and moon both rotate around a common point, their combined center of massThis rotation produces a centrifugal force

TidesCentrifugal force: The force that tends to push a body away from the center of rotationforce that pushes you outward on a merry-go-roundbalances the gravitational attraction between the earth and moonwithout it the two would either fly away from each other or crash together

Tidescentrifugal force and the moons gravity are not in perfect balance everywhere along the earths surfacethe side of the earth nearest the moon, the moons gravity is strongerpulls water towards the moonside away from the mooncentrifugal force is strongerpushes water away from the moon

Tides

TidesEarth is spinning on its axisany given point on the earths surface will be the first under a bulge then away from a bulgehigh tide occurs when that point is under the bulge

TidesEarth takes 24 hours to complete a rotationMoon advances a little on its orbit every day full tidal cycle takes 24 hours and 50 minutes

TidesTidal range: difference in water level between successive high and low tides

TidesSun produces tidal bulges in the same way as the moonSun is larger than the moon but 400 times further awayeffect of the sun on the tides is half that of the moon

TidesWhen the sun and the moon are in line with each other, full moons and new moons the effects are added togethertidal range becomes large

Tidesspring tides: the tides with a large tidal wave, occur around the time of new or full moonsoccur once every two weeks

TidesWhen the sun and moon are at right angles their effects partially cancel each otherNeap Tides: tides with a small tidal rangeOccurs when the moon is in quarter (first or third)

Tides in the Real World

TidesTides in the real world behave slightly differently They vary based on:1. location2. shape of the basin3. depth of the basin

TidesThere are three types of tidal occurrences:1. semi-diurnal2. mixed semi-diurnal3. diurnal

TidesSemidiurnal tides: A tidal pattern with two high and two low tides each dayEast coast of N. America most of Europe and Africa

TidesMixed Semidiurnal tides: A tidal pattern with two successive high tides of different heights each dayWest coast of N. America and Canada

TidesDiurnal tides: One high and one low tide every dayuncommoncoast of Antarctica and parts of the Gulf of Mexico Caribbean and Pacific

TidesTide Tables: A table that gives the predicted time and height of tides for particular points along a coastgive values for one particular place

Tides

TidesEffected by channels, reefs, basins and other local featuresWeather patterns also effect tidesstrong winds, can pile water up on shore