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 30° N&S latitudeSurplus heat between 30° N&S latitude Heat deficit between 30°-90° N&S latitudeHeat deficit between 30°-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 – Atmosphere – Ocean currents

Salinity in Oceans – Total amount of dissolved solids expressed in grams in 1 kg of water Average salinity in oceans = 35 ‰Average salinity in oceans = 35 ‰ Salinity variationsSalinity variations – Due to differences in local rates of evaporation and precipitation (water budget) – 35 parts per thousand (ppt) – 35 g/kg SalinitySalinity

Constituents of Sea Water Most abundant seawater elements are sodium (Na + ) + chloride (Cl - ) Most abundant seawater elements are sodium (Na + ) + chloride (Cl - ) Minor and trace elements also presentMinor and trace elements also present Major constituents: SO 4 2-, Mg 2+, Ca 2+, K +, and HCO 3 -Major constituents: SO 4 2-, Mg 2+, Ca 2+, K +, and HCO 3 -

Seawater versus River Water Chemical Constituent Percent of total salt content OceanRiver Silica (SiO 2 ) Iron (Fe) Calcium (Ca) Magnesium (Mg) Sodium (Na) Potassium (K) Bicarbonate (HCO 3 ) Sulfate (SO 4 2- ) Chloride (Cl) Nitrate (NO 3 ) Bromide (Br) TOTAL Note Silica and Calcium more abundant in Rivers. Why? If salt consistently added to oceans, why aren’t they getting saltier?

Salts in the Ocean – Salts going in = salts going out Salts come from:Salts come from: – Rocks = cations – Gases from mantle Why is the ocean not getting saltier?Why is the ocean not getting saltier?

Salts Going Out Sea Sra Sea Sra Sea SpraySea Spray BiologicalBiological – Fecal pellets – Shell formation Mid-ocean ridge magmaMid-ocean ridge magma EvaporitesEvaporites AdsorptionAdsorption

Principle of Constant Proportions – Because of this principle, it is necessary to test for 1 salt ion (usually Cl) to determine total amount of salt present – The amount of salt varies, but the relative proportions of ions are constant

Density of Water TemperatureTemperature SalinitySalinity Density of water is affected by: – Below 4°C, density decreases – At 0°C, ice forms, density decreases rapidly – As water first cools, density increases and volume decreases – Adding salts increasesdensity – Adding salts increases density – Fresh H 2 0 floats on salt H 2 0

Unique Property of Water When liquid H 2 0 loses heat and temperature lowers to freezing point, ice formsWhen liquid H 2 0 loses heat and temperature lowers to freezing point, ice forms Water expands as it freezesWater expands as it freezes Ice less dense than water – ice floatsIce less dense than water – ice floats Why does ice float on water? – Angle between H and O atoms in H 2 0 molecule increases from 105° to 109°

Density of Water

Ocean Salinity Sea Surface Temperatures August 27,

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

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 Temperature, Salinity, Oxygen Profile

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

Water Masses Identified by T-S Diagrams soconnell.web.wesleyan.edu

Water Masses soconnell.web.wesleyan.edu

Figure 6.6 Water transported by the atmosphere into and out of the Atlantic. Basins draining into the Atlantic are black, deserts are white, and other drainage basins are shaded. Arrows give direction of water transport by the atmosphere, and values are in Sverdrups. Bold numbers give the net transport for the Atlantic. Overall, the Atlantic loses 0.32Sv, an amount approximately equal to the flow in the Amazon River. From Broecker (1997). Figure 6.6 Water transported by the atmosphere into and out of the Atlantic. Basins draining into the Atlantic are black, deserts are white, and other drainage basins are shaded. Arrows give direction of water transport by the atmosphere, and values are in Sverdrups. Bold numbers give the net transport for the Atlantic. Overall, the Atlantic loses 0.32Sv, an amount approximately equal to the flow in the Amazon River. From Broecker (1997).

Thermocline Zone of rapid temperature increase Zone of rapid temperature increase Surface waters warmer; deeper colder Surface waters warmer; deeper colder polar seas (high latitude) as cold as -2 degrees Celsius (28.4 degrees Fahrenheit) while Persian Gulf (low latitude) as warm as 36 degrees Celsius (96.8 degrees Fahrenheit) polar seas (high latitude) as cold as -2 degrees Celsius (28.4 degrees Fahrenheit) while Persian Gulf (low latitude) as warm as 36 degrees Celsius (96.8 degrees Fahrenheit)

Ocean Conveyor Belt Atlantic Current move northward Atlantic Current move northward –Evaporation occurs, heat release, water cools and sinks –Heat release warms area Dense water flows in ocean basins Dense water flows in ocean basins Transport heat, solids, gases to all oceans Transport heat, solids, gases to all oceans Most deep water upwells in Southern Ocean t 1600 year later Most deep water upwells in Southern Ocean t 1600 year later Termed thermohaline circulation Termed thermohaline circulation

Importance of Thermohaline Circulation to Climate Transport heat to poles Transport heat to poles –Regulates amount of sea ice Impact amount of CO2 in atmosphere Impact amount of CO2 in atmosphere Norway and Manitoba, Canada same latitude; Norwary 20 degrees warmer Norway and Manitoba, Canada same latitude; Norwary 20 degrees warmer

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Halocline Halocline is zone of rapid salinity increase Halocline is zone of rapid salinity increase Less salty on surface Less salty on surface

Pycnocline Density of pure water is 1000 kg/m3 Density of pure water is 1000 kg/m3 Density increase with depth Density increase with depth Zone of rapid increase is pycnocline Zone of rapid increase is pycnocline

Temp, Salinity, Density profile of South Atlantic (45S 50W) Note T decreases & S0/00 increases with depth Note T decreases & S0/00 increases with depth Results in density increase Results in density increase