The Properties of Sea Water

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

2. Where’s the Water? • Reservoir Volume (106 km3) PercentOcean 1370 97.3Ice (polar) 29 2.1Groundwater 5 0.4Lakes 0.1 0.01Atmosphere 0.01 0.001Rivers 0.001 0.0001

3. Where did the water in the Oceans come from? • Outgassing (H2O, CO2) of the Earth from volcanoes, early in its history, but continuing today • Sedimentary rocks as old as 3.8 billion years! • A much smaller amount from comets that pass by

4. The Water Molecule

5. Water is a “Polar” Molecule • Weak electrical attraction makes for “sticky” molecules • This explains its unique properties:heat capacitysurface tensiondissolving power

6. Temperature vs Heat • Temperature is a measure of how fast the molecules in a substance are moving • Heat 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 • Sensible heat is what we sense from different temperatures; energy needed to raise T (or released to decrease T) • Latent heat is the energy needed to change state (ice to water, water to vapor)

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

10. solid liquid gas Changes of state Water co-exists on the Earth in 3 physical states:Habitable Planet

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. Evaporationfrom lakes, oceans, rivers, etc. occurs for temperatures lower than 100 oC But it requires more energy to do so

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

15. Density of Pure Water

16. Consequences…

17. Consequences Bottom temperature of deep, cold lakes is always 4 oC. 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 • Density of solid is less than liquid • Melting and boiling points are very high • Highest heat capacity • High heat of fusion and vaporization • Tremendous dissolving power

20. Dissolving Power of Water

21. Why is the Ocean Salty? • Total dissolved solids (called “salinity”) • About 3.5% by weight (average seawater) • Usually expressed as 35 0/00 (parts per thousand, ppt) • Varies geographically according to Evaporation, Precipitation, and Rivers

22. The Most Abundant Ions • Chloride (Cl-) 19.0 g/kg • Sodium (Na+) 10.6 “ • Sulfate (SO42-) 2.6 “ • Magnesium (Mg2+) 1.2 “ • Calcium (Ca2+) 0.4 “ • Potassium (K+) 0.4 “ 35.2 g/kg

23. Ions in Sea Water • Anions are negatively chargedexamples: Cl-, SO4- • Cations are positively chargedexamples: Na+, K+, Ca++, Mg++

24. Measuring Salinity • Principle ofConstant Proportionse.g., SO42-/Cl- is a constant, independent of salinity • This means we need measure only one ion to get salinity; i.e., Cl- • Today salinity is measured quickly by electrical conductivity of sea water

25. Where does Salinity come from? • Terrigenous input (rivers, dust, ash) • Hydrothermal vents • Dissolving old sediments (evaporites) • Steady State: Inputs equal Outputs

26. Weathering of Rocks • H2O + CO2 ---> H2CO3 (carbonic acid) • “acid” rain, pH ~4-5; environmental concerns (HCl, HF, H2SO4) • Dissolves rock minerals into ions, which travel down rivers to the ocean

27. Residence Time • How 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 SeaRate entering or exiting

28. Residence Time • For water entering through rivers, the residence time is about Volume=1370x106 km3 (oceans) Flux 0.037x106 km3/yr (rivers) = 35,000 years.For Cl-, the residence time is 100 Ma!For Fe2+, the residence time is 200 yrWhich is likely to obey Constant Proportions?

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

30. The Hydrologic Cycle

31. Evaporation - Precipitation • Over the oceans, evaporation exceeds precipitation • The 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 ? saltier fresher  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: • Water is a polar molecule -- unique properties (melting pt, heat capacity, dissolving power, water denser than ice) • Salinity is the total dissolved solids • Salinity in the surface ocean varies by Evaporation - Precipitation • Principle ofConstant Proportions • Residence Time in the Oceans