Heat Heat &&

Deep Ocean CurrentsDeep Ocean Currents

Heat VariationsHeat VariationsLatitudeLatitude

• Depends on angle sunlight hits Depends on angle sunlight hits surfacesurface– At equator, sunlight covers less area; more At equator, sunlight covers less area; more

heat heat

– Sunlight at polar latitudes covers wider area; therefore, Sunlight at polar latitudes covers wider area; therefore, less heatless heat

– Mid latitude heating affected by seasonsMid latitude heating affected by seasons

Heat VariationsHeat VariationsSeasonsSeasons

• Earth’s axis tilted 23.5Earth’s axis tilted 23.5° - ° - orbital inclinationorbital inclination– Northern hemisphere – maximum solar energy in Northern hemisphere – maximum solar energy in

summersummer– Southern hemisphere – max. solar energy in our winterSouthern hemisphere – max. solar energy in our winter

Heat BudgetHeat Budget• Heat input = Heat outputHeat input = Heat output

• 100 units = 30 units + 100 units = 30 units + 70 units70 units(from sun)(from sun) (Reflected)(Reflected) (heat Earth)(heat Earth)

• 70 units70 units = 47 units + 23 units = 47 units + 23 units(absorbed by surface)(absorbed by surface)(by atmosphere)(by atmosphere)

Annual Incoming Solar Annual Incoming Solar RadiationRadiation

•Surplus heat between 38Surplus heat between 38°° N&S latitude N&S latitude

• Heat deficit between 38Heat deficit between 38°°-90-90°° N&S latitude N&S latitude

Why don’t oceans evaporate at equator and freeze at poles?Why don’t oceans evaporate at equator and freeze at poles?

Heat TransferHeat Transfer

• Heat is transferred from equator to polesHeat is transferred from equator to poles– Air CirculationAir Circulation– Ocean currentsOcean currents

SalinitySalinityEvaporation and PrecipitationEvaporation and Precipitation

•Evaporation and precipitation control Evaporation and precipitation control S S ‰‰

• Evaporation > Evaporation > Precipitation = Precipitation = ↑ S ↑ S ‰‰

– Freezing Freezing ↑↑ S S ‰‰

• 00° (equator); 40°-60° N&S° (equator); 40°-60° N&S– Precipitation > EvaporationPrecipitation > Evaporation

– Lower S ‰Lower S ‰

• 1010°-40° N&S°-40° N&S– Evaporation > PrecipitationEvaporation > Precipitation

– High S ‰High S ‰

• 6060°-90° N&S (Polar Region)°-90° N&S (Polar Region)

Ocean SalinitiesOcean Salinities

• S ‰ variations lead to density stratificationS ‰ variations lead to density stratification– ↑ ↑ S ‰; S ‰; ↑density↑density– Denser HDenser H22O sinksO sinks

• Example of stratification (layering) is Atlantic OceanExample of stratification (layering) is Atlantic Ocean

• Two factors that control densityTwo factors that control density– S S ‰‰

– TemperatureTemperature

Atlantic Water MassesAtlantic Water MassesDensity Driven CurrentsDensity Driven Currents

•Atlantic consists of intermediate, deep, and bottom watersAtlantic consists of intermediate, deep, and bottom waters

• Thickness and extent depends on:Thickness and extent depends on:– Rate of formationRate of formation

– Size of region where formedSize of region where formed

Pacific OceanPacific Ocean

• Pacific Ocean not well definedPacific Ocean not well defined– Small region where water formsSmall region where water forms– Limited HLimited H22O supply from northO supply from north

Atlantic Water FlowAtlantic Water Flow

• Dense, cold Polar HDense, cold Polar H22O sinksO sinks

• Current driven by density contrastCurrent driven by density contrast

• Identify water masses by T-S curve and biologyIdentify water masses by T-S curve and biology

AtlanticAtlanticDeep Water CirculationDeep Water Circulation

• Currents extensive and interconnectedCurrents extensive and interconnected

Upwelling and DownwellingUpwelling and Downwelling

• Wind blows HWind blows H22O horizontallyO horizontally

• Deeper HDeeper H22O rises to O rises to replace surface Hreplace surface H22OO

• UpwellingUpwelling – process of – process of HH22O risingO rising

• Winds moving toward Winds moving toward shore cause Hshore cause H22O to move O to move downwarddownward

• DownwellingDownwelling – process – process of Hof H22O sinkingO sinking

Equatorial UpwellingEquatorial Upwelling

• Deep, nutrient-rich HDeep, nutrient-rich H22O is brought to the surfaceO is brought to the surface