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Music today: Billy Ocean, “Get Outta My Dreams and Into My Car”

Dive deep into the fascinating world of water properties and salinity levels in oceans. Learn about the origins of ocean water and the factors influencing salinity. Discover the unique characteristics of water molecules and the role they play in shaping our planet’s climate.

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Music today: Billy Ocean, “Get Outta My Dreams and Into My Car”

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  1. Music today: Billy Ocean, “Get Outta My Dreams and Into My Car” • Find your Midterm Exam score at the class web site, under “Lectures”, April 19 • Scantrons and Short Answers will be returned at Labs

  2. The Properties of Sea Water Reading: Chapter 5, pp. 133-151

  3. 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

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

  5. The Water Molecule

  6. Water is a “Polar” Molecule • This explains its unique properties • Exists in three states on the planet surface

  7. water vapor ice liquid water

  8. Table 4.2 (6th edition)

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

  10. Sensible Heat vs Latent Heat • Sensible heat is what we sense from different temperatures • Latent heat is the energy needed to change state (ice to water, water to vapor)

  11. 3 Physical States of Water:

  12. Evaporation from lakes, oceans, rivers, etc. occurs for temperatures lower than 100 oC

  13. 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

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

  15. 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

  16. Structure of Solid Water (Ice)

  17. Dissolving Power of Water

  18. Why is the Ocean Salty?What is Salinity? • Total dissolved solids • 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

  19. 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

  20. Ions in Sea Water • Anions are negatively chargedCl-, SO4- • Cations are positively chargedNa+, K+, Ca++, Mg++

  21. Measuring Salinity • Principle of Constant 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

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

  23. 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

  24. Residence Time • How long do the various dissolved ions stay in the ocean? Depends on reactivity. • Residence Time: The average time spent by a substance in the Ocean = Amount in SeaRate entering or exiting

  25. 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?

  26. Adding salt lowers the freezing temperature: Seawater freezes at about -2 oC

  27. Salinity and Temperature

  28. The Hydrologic Cycle

  29. Evaporation - Precipitation • Over the oceans, evaporation exceeds precipitation • The balance is restored by rain over the continents, returning water via rivers

  30. Desalination

  31. Salt in the Ocean and its relationship to density Average ocean salinity 35 per mil 1000 g of seawater = 965 g of water + 35 g salt If all of the water in the oceans evaporated, this amount of salt would form a layer roughly 45 m thick over the entire surface of the Earth

  32. Surface salinities

  33. Evaporation vs Precipitation

  34. Sea-Surface Salinitywhich ocean is saltier?

  35. Which ocean is Saltier? • In spite of the fact that many more 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

  36. 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 varies according to Evaporation - Precipitation • Principle of Constant Proportions • Residence Time in the Oceans

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