Class 15 -- The OceansClass 15 -- The OceansPROPERTIES OF SEA WATERPROPERTIES OF SEA WATER

SalinitySalinityEffect of salinity on physical Effect of salinity on physical propertiesproperties

ENERGY TRANSMISSION/ABSORPTION ENERGY TRANSMISSION/ABSORPTION IN WATER AND SEA WATERIN WATER AND SEA WATER

HeatHeatLightLight

•Salinity Salinity - - amt. of dissolved salts; symbol = S - - amt. of dissolved salts; symbol = S•Average S = 35 g/kg (p.p.t., ‰)Average S = 35 g/kg (p.p.t., ‰)•Range (most sea water): 30 -37 ‰Range (most sea water): 30 -37 ‰

How does sea water differ from fresh water?How does sea water differ from fresh water?•Greater S --> greater densityGreater S --> greater density•Dissolved salts change water properties…Dissolved salts change water properties…

– Boiling point higher = 103˚CBoiling point higher = 103˚C– Freezing point lowered...Freezing point lowered...

SEA WATER (= Ocean water):SEA WATER (= Ocean water):

•Freezing of sea water: 1- salt exclusionFreezing of sea water: 1- salt exclusion-- B-- Beginsegins to freeze at -2˚C to freeze at -2˚C-- Salt is excluded from the ice that is formed.-- Salt is excluded from the ice that is formed.-- Remaining water saltier, so...-- Remaining water saltier, so...-- This water freezes at lower temp-- This water freezes at lower temp..

-- As seawater cools below 4˚C, density -- As seawater cools below 4˚C, density increases increases

–Very important: This means that the coldest Very important: This means that the coldest sea water sinks to the bottom.sea water sinks to the bottom.–Oceans not stratified like lakes in winter Oceans not stratified like lakes in winter

Density of sea water just aboveDensity of sea water just above the freezing pointthe freezing point

-- As seawater cools below 4˚C, density increases -- As seawater cools below 4˚C, density increases –Unlike fresh water lakesUnlike fresh water lakes–Very important: This means that the coldest Very important: This means that the coldest sea water sinks to the bottom.sea water sinks to the bottom.–This creates deep currents (more later)This creates deep currents (more later)

Density of seawaterDensity of seawater--... Higher S water is denser... Higher S water is denser... Colder water is denser... Colder water is denserVery important! Remember convection:Very important! Remember convection:• Dense water at ocean surface SINKS in places Dense water at ocean surface SINKS in places where water iswhere water is

– coldest and/orcoldest and/or– salinity is highest, caused bysalinity is highest, caused by

– freezingfreezing– evaporationevaporation

•““Deep water” currents come from these areasDeep water” currents come from these areas

Why is the ocean blue?Why is the ocean blue?

How deep does sunlight How deep does sunlight penetrate into the oceans?penetrate into the oceans?

How does solar energy get How does solar energy get absorbed by the ocean?absorbed by the ocean?

• Radiant energy = Radiation -- direct Radiant energy = Radiation -- direct transmission, through space, air, water, etc. transmission, through space, air, water, etc.

• Different wavelength (Different wavelength () waves are different ) waves are different colors of light, different types of radiant energycolors of light, different types of radiant energy

• Solar energy- many Solar energy- many ’s’s combinedcombined

Sunlight energy transmission and absorptionSunlight energy transmission and absorption by waterby water

Fig. 13.3

Absorption of solar radiationAbsorption of solar radiation by the oceansby the oceans

•Sun’s rays reaching the sea surface:Sun’s rays reaching the sea surface:• visiblevisible• infrared = heatinfrared = heat• ultravioletultraviolet

•Absorption by ocean water is strong, but Absorption by ocean water is strong, but depends on wavelength...depends on wavelength...

Depth % absorbed wavelengths absorbed1 m 60 infrared (heats surface waters)

10 m 80 longer visible150 m 99 [only short, green-blue-violet light

remains]

How muchHow much energy or light is absorbed energy or light is absorbed at various depths?at various depths?

What kind ofWhat kind of energy or light is absorbed energy or light is absorbed at various depths?at various depths?

•Photosynthesis <150 metersPhotosynthesis <150 meters•Heating from sun only affects top several Heating from sun only affects top several metersmeters•Blue color of sea water: only shorter Blue color of sea water: only shorter wavelengths at depthwavelengths at depth

Consequences:Consequences:

Photosynthesis limited to top <150 mPhotosynthesis limited to top <150 m

Water vapor = “latent” heat

Heat

Within The Oceans

Conduction -- Conduction -- heat energy transfer between touching heat energy transfer between touching substances: warm to coolsubstances: warm to cool•Surface of the ocean <--> atmosphere Surface of the ocean <--> atmosphere

•conduction importantconduction important•BUT only affects the top few metersBUT only affects the top few meters

•Conduction between surface of ocean Conduction between surface of ocean and deep water – not muchand deep water – not much

•Water is a poor heat conductor over Water is a poor heat conductor over long distanceslong distances•Example: Water at 1000m depth near Example: Water at 1000m depth near Bahamas is barely above freezing!Bahamas is barely above freezing!

Warm Climate Zones: Warm surface layer+ cold water below

Stratification

Convection very important in the atmosphere and the oceans

Atmosphere- Heated at bottom, cooled at top

ConvectionHeat or “coldness” moves

with density-driven currents

Cooling

Heating

Convection in the Oceans-Convection in the Oceans- Cooling of surface water in far north, far southCooling of surface water in far north, far southWarming of surface water at low latitudeWarming of surface water at low latitude

CoolingCooling HeatingHeating

North AtlanticNorth Atlantic EquatorEquator