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The Properties of Sea Water What makes water so special? Why is the ocean salty? What makes water so special? Why is the ocean salty?

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Presentation on theme: "The Properties of Sea Water What makes water so special? Why is the ocean salty? What makes water so special? Why is the ocean salty?"— Presentation transcript:

1 The Properties of Sea Water What makes water so special? Why is the ocean salty? What makes water so special? Why is the ocean salty?

2 Where’s the Water? FReservoirVolume (10 6 km 3 )Percent Ocean Ice (polar) Groundwater Lakes Atmosphere Rivers

3 Where did the water in the Oceans come from? FOutgassing (H 2 O, CO 2 ) of the Earth from volcanoes, early in its history, but continuing today FSedimentary rocks as old as 3.8 billion years! FA much smaller amount from comets that pass by FOutgassing (H 2 O, CO 2 ) of the Earth from volcanoes, early in its history, but continuing today FSedimentary rocks as old as 3.8 billion years! FA much smaller amount from comets that pass by

4 The Water Molecule

5 Water is a “Polar” Molecule FWeak electrical attraction makes for “sticky” molecules FThis explains its unique properties: heat capacity surface tension dissolving power FWeak electrical attraction makes for “sticky” molecules FThis explains its unique properties: heat capacity surface tension dissolving power

6 Temperature vs Heat FTemperature is a measure of how fast the molecules in a substance are moving FHeat is a measure of how much energy has to be put into (or gotten out of) a substance to change its temperature, or “state” (solid, liquid, gas) FTemperature is a measure of how fast the molecules in a substance are moving FHeat is a measure of how much energy has to be put into (or gotten out of) a substance to change its temperature, or “state” (solid, liquid, gas)

7 Sensible Heat vs Latent Heat HSensible heat is what we sense from different temperatures; energy needed to raise T (or released to decrease T) HLatent heat is the energy needed to change state (ice to water, water to vapor) HSensible heat is what we sense from different temperatures; energy needed to raise T (or released to decrease T) HLatent heat is the energy needed to change state (ice to water, water to vapor)

8

9 ice water vapor liquid water Exists in three states on the planet surface

10 Changes of state Water co-exists on the Earth in 3 physical states: Habitable Planetsolidliquidgas

11 Changes of state always occur at constant temperature The heat needed for a change of state is called latent heat

12 Heat and the three Physical States of Water:

13 Evaporation from lakes, oceans, rivers, etc. occurs for temperatures lower than 100 o C But it requires more energy to do so

14 Energy removed from surface (evaporation) Energy liberated into the atmosphere (condensation) Major source of energy to power the Earth’s weather systems

15 Density of Pure Water

16 Consequences…

17 Consequences Bottom temperature of deep, cold lakes is always 4 o C. Ice floats on the water surface, so fish survive. Pipes (or beer bottles) can freeze and burst.

18 Surface tension - measure of how difficult it is to stretch or break the surface of a liquid Water has the highest surface tension of all common liquids

19 Special Properties of Water FDensity of solid is less than liquid FMelting and boiling points are very high FHighest heat capacity FHigh heat of fusion and vaporization FTremendous dissolving power FDensity of solid is less than liquid FMelting and boiling points are very high FHighest heat capacity FHigh heat of fusion and vaporization FTremendous dissolving power

20 Dissolving Power of Water

21 Why is the Ocean Salty? FTotal dissolved solids (called “salinity”) FAbout 3.5% by weight (average seawater) FUsually expressed as 35 0 / 00 (parts per thousand, ppt) FVaries geographically according to Evaporation, Precipitation, and Rivers FTotal dissolved solids (called “salinity”) FAbout 3.5% by weight (average seawater) FUsually expressed as 35 0 / 00 (parts per thousand, ppt) FVaries geographically according to Evaporation, Precipitation, and Rivers

22 The Most Abundant Ions FChloride (Cl - )19.0 g/kg FSodium (Na + )10.6 “ FSulfate (SO 4 2- ) 2.6 “ FMagnesium (Mg 2+ ) 1.2 “ FCalcium (Ca 2+ ) 0.4 “ FPotassium (K + ) 0.4 “ 35.2 g/kg FChloride (Cl - )19.0 g/kg FSodium (Na + )10.6 “ FSulfate (SO 4 2- ) 2.6 “ FMagnesium (Mg 2+ ) 1.2 “ FCalcium (Ca 2+ ) 0.4 “ FPotassium (K + ) 0.4 “ 35.2 g/kg

23 Ions in Sea Water FAnions are negatively charged examples: Cl -, SO 4 - FCations are positively charged examples: Na +, K +, Ca ++, Mg ++ FAnions are negatively charged examples: Cl -, SO 4 - FCations are positively charged examples: Na +, K +, Ca ++, Mg ++

24 Measuring Salinity FPrinciple of Constant Proportions e.g., SO 4 2- /Cl - is a constant, independent of salinity FThis means we need measure only one ion to get salinity; i.e., Cl - FToday salinity is measured quickly by electrical conductivity of sea water FPrinciple of Constant Proportions e.g., SO 4 2- /Cl - is a constant, independent of salinity FThis means we need measure only one ion to get salinity; i.e., Cl - FToday salinity is measured quickly by electrical conductivity of sea water

25 Where does Salinity come from? FTerrigenous input (rivers, dust, ash) FHydrothermal vents FDissolving old sediments (evaporites) FSteady State: Inputs equal Outputs FTerrigenous input (rivers, dust, ash) FHydrothermal vents FDissolving old sediments (evaporites) FSteady State: Inputs equal Outputs

26 Weathering of Rocks FH 2 O + CO 2 ---> H 2 CO 3 (carbonic acid) F“acid” rain, pH ~4-5; environmental concerns (HCl, HF, H 2 SO 4 ) FDissolves rock minerals into ions, which travel down rivers to the ocean FH 2 O + CO 2 ---> H 2 CO 3 (carbonic acid) F“acid” rain, pH ~4-5; environmental concerns (HCl, HF, H 2 SO 4 ) FDissolves rock minerals into ions, which travel down rivers to the ocean

27 Residence Time FHow long do the various dissolved ions stay in the ocean? Depends on how “reactive”.  Residence Time: The average time spent by a substance in the Ocean = Amount in Sea Rate entering or exiting FHow long do the various dissolved ions stay in the ocean? Depends on how “reactive”.  Residence Time: The average time spent by a substance in the Ocean = Amount in Sea Rate entering or exiting

28 Residence Time FFor water entering through rivers, the residence time is about Volume = 1370x10 6 km 3 (oceans) Flux 0.037x10 6 km 3 /yr (rivers) = 35,000 years. For Cl -, the residence time is 100 Ma! For Fe 2+, the residence time is 200 yr Which is likely to obey Constant Proportions?

29 Adding salt lowers the freezing temperature: Seawater freezes at about -2 o C Freezing removes fresh water, leaves salt

30 The Hydrologic Cycle

31 Evaporation - Precipitation FOver the oceans, evaporation exceeds precipitation FThe balance is restored by rain over the continents, returning water via rivers FOver the oceans, evaporation exceeds precipitation FThe balance is restored by rain over the continents, returning water via rivers

32 Salt in the Ocean increases its density

33 Ocean Surface salinities

34 Evaporation vs Precipitation

35 Which processes change the surface salinities ? saltierfresher  evaporation  precipitation  sea ice formation  sea ice melting  freshwater runoff from land

36 Which ocean is the saltiest?

37 The Atlantic!  In spite of the fact that many BIG rivers empty into the Atlantic than the Pacific, the Atlantic is actually significantly saltier because of the evaporation-precipitation cycle and the Isthmus of Panama plus input from the Mediterranean Sea

38 Surface salinities Evaporation, precipitation, and wind patterns explain high/low salinity of Atlantic/Pacific.

39 Summary: èWater is a polar molecule -- unique properties (melting pt, heat capacity, dissolving power, water denser than ice) èSalinity is the total dissolved solids èSalinity in the surface ocean varies by Evaporation - Precipitation èPrinciple of Constant Proportions èResidence Time in the Oceans èWater is a polar molecule -- unique properties (melting pt, heat capacity, dissolving power, water denser than ice) èSalinity is the total dissolved solids èSalinity in the surface ocean varies by Evaporation - Precipitation èPrinciple of Constant Proportions èResidence Time in the Oceans


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