Heat & Deep Ocean Currents

Heat Variations Latitude Depends on angle sunlight hits surface Depends on angle sunlight hits surface – At equator, sunlight covers less area; more heat – Sunlight at polar latitudes covers wider area; therefore, less heat – Mid latitude heating affected by seasons

Heat Variations Seasons Earth’s axis tilted 23.5° - orbital inclination Earth’s axis tilted 23.5° - orbital inclination – Northern hemisphere – maximum solar energy in summer – Southern hemisphere – max. solar energy in our winter

Heat Budget Heat input = Heat output Heat input = Heat output 100 units = 30 units + 70 units100 units = 30 units + 70 units (from sun) (Reflected) (heat Earth) 70 units = 47 units + 23 units70 units = 47 units + 23 units (absorbed by surface) (by atmosphere)

Annual Incoming Solar Radiation Surplus heat between 38° N&S latitudeSurplus heat between 38° N&S latitude Heat deficit between 38°-90° N&S latitudeHeat deficit between 38°-90° N&S latitude Why don’t oceans evaporate at equator and freeze at poles?

Heat Transfer Heat is transferred from equator to polesHeat is transferred from equator to poles – Air Circulation – Ocean currents

Salinity Evaporation and Precipitation Evaporation and precipitation control S ‰Evaporation and precipitation control S ‰ Evaporation > Precipitation = ↑ S ‰Evaporation > Precipitation = ↑ S ‰ – Freezing ↑ S ‰ 0° (equator); 40°-60° N&S0° (equator); 40°-60° N&S – Precipitation > Evaporation – Lower S ‰ 10°-40° N&S10°-40° N&S – Evaporation > Precipitation – High S ‰ 60°-90° N&S (Polar Region)60°-90° N&S (Polar Region)

Ocean Salinities S ‰ variations lead to density stratificationS ‰ variations lead to density stratification – ↑ S ‰; ↑ density – Denser H 2 O sinks Example of stratification (layering) is Atlantic OceanExample of stratification (layering) is Atlantic Ocean Two factors that control densityTwo factors that control density – S ‰ – Temperature

Atlantic Water Masses Density 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 formation – Size of region where formed

Pacific Ocean Pacific Ocean not well definedPacific Ocean not well defined – Small region where water forms – Limited H 2 O supply from north

Atlantic Water Flow Dense, cold Polar H 2 O sinksDense, cold Polar H 2 O 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

Atlantic Deep Water Circulation Currents extensive and interconnectedCurrents extensive and interconnected

Upwelling and Downwelling Wind blows H 2 O horizontallyWind blows H 2 O horizontally Deeper H 2 O rises to replace surface H 2 ODeeper H 2 O rises to replace surface H 2 O Upwelling – process of H 2 O risingUpwelling – process of H 2 O rising Winds moving toward shore cause H 2 O to move downwardWinds moving toward shore cause H 2 O to move downward Downwelling – process of H 2 O sinkingDownwelling – process of H 2 O sinking

Equatorial Upwelling Deep, nutrient-rich H 2 O is brought to the surfaceDeep, nutrient-rich H 2 O is brought to the surface