The Water Planet

1. The Water Planet The Blue Planet • Most of the Earth’s surface is covered by water (71%) • 97% of this water is salt water • 3% of this water is fresh water

2. Human primarily need fresh water • There’s just not as much as we’d like, and not all the sources are accessible. • Plenty of water exists at the poles, for instance, but it’s frozen and located far from population centers. • We can condense water vapor from the atmosphere by artificial means, but only at an astounding cost. • Most of the fresh water we rely on comes from underground aquifers and rivers.

4. Why study water? • as the human population increases, the demand for fresh water will increase. • Most of the habitable area of Earth is water

5. Water’s unique properties Water is a POLAR molecule

6. Unique properties of water Water’s polarity allows it to bond to other water molecules Notice the hydrogen bonds resulting from the slightly positively charged hydrogen part of one water molecule attracted to the slightly negatively charged oxygen part of another water molecule.

7. Effects of hydrogen bonds • Liquid Water. The most important characteristic of hydrogen bonds is their ability to make water a liquid at room temperature. • Cohesion: Because hydrogen bonds attract water molecules to each other, water molecules tend to stick together. • Adhesion: Water also sticks to other materials due to its polar nature. This is called adhesion. • Capillary Action: Combination of cohesion and adhesion – example: water moves up trees

8. Effects of hydrogen bonds • Surface Tension – cohesion at surface of water • “skin like surface” • Important for small organisms like this water strider or plankton

9. Effects of hydrogen bonds Why does ice float?

10. Ice is less dense than water because the molecules form a lattice structure as the substance freezes. The small iceberg in the sea demonstrates this property as the it slowly melts and floats along the surface.

11. This "open lattice structure" of water molecules is shown for solid ice. Open space between the molecules illustrates why ice is less dense than liquid water.

12. 3 Density layers of the Ocean • Surface zone - Temperature • relatively constant here because waves and • currents continually mix the water 2% of ocean • Thermocline- - separates warm surface water from cool deep waters …rapid temperature changes with depth. 18% ocean • Below the thermocline is the deep zone layer. This layer is cold, dense. • 80% ocean

13. a. If ice sank, the ocean would be entirely frozen—or at least substantially cooler—because water would not be able to retain as much heat. b. The Earth’s climate would be substantially colder—perhaps too cold for life at all. c. Ice allows animals like polar bears to float and hunt for food and build dens. It is a critical part of their habitat

14. Seawater is a solution, just like tea coffee or lemonade! • Solvent = Water is called the universal solvent as many substances dissolve in it. • Solute = the substance that dissolves Ex: salt, sugar, • Solution = a uniform mixture of two or more substances Ex: tea, coffee, lemonade, • Solubility of a substance is its ability to be dissolved in a solvent • Saturated = when no more solute will dissolve in the solvent, it is saturated.

15. Effects of hydrogen bonds Water is a great solvent

16. Salinity – the measure of the amount of dissolved salts in water Salinity includes the total quantity or concentration of all dissolved salts. This is the sodium chloride and everything else.

17. Measure Salinity? • How well does water conduct electricity • Ratio of the conductivity of the sample compared to the conductivity of a standard solution of potassium chloride (KCl).

18. Salinity • Salinity is expressed in parts per thousand because even very small variations are significant. • The ocean’s average salinity is 35‰ • The abbreviation ‰ stands for “parts per thousand,” so 35‰ means 35 parts per thousand. • Note: To convert parts per thousand into percent, you divide by 10, so that 35‰ = 3.5%

19. Why is the Sea Salty? How does salt get into the sea? Does Salt ever leave the ocean? • From land, carried by streams and rivers through erosion • From inside the earth through volcanos and hydrothermal vents on the seafloor • From the atmosphere – particles are carried by wind and deposited into the ocean. • Salt remains in the ocean unless they become incorporated into the sediments and rocks on the seafloor.

20. Salinity varies within ocean • Surface ocean salinity varies with the season and with the weather, particularly with rainfall and evaporation: • Rainfall decreases salinity by adding fresh water. • Evaporation increases salinity by removing fresh water. • Freshwater input from rivers lowers salinity.

21. The solubility varies with temperature of the water. • As temperature increases, so does its solubility. • More evaporation in tropical regions results in more evaporation of water vapor, therefore increasing the salinity at the surface. • Most areas of high salinity found near equator. • Most areas of low salinity found near poles.

23. Brackish water = mixture of fresh and salt water Salinity in the ocean varies Has a salinity somewhere between salt water and fresh water. Typically found in estuaries, areas where rivers meet the sea. Salinities in estuaries vary from 1 – 40 psu. Varies with the temperature and season.

24. What is an estuary? An area where fresh water and seawater mix Example: Indian River lagoon • Organisms which live there must be able to live in a variety of salinity levels, depending on the amount of rain and evaporation

25. Density Density = mass / volume D=m/ v Vol. is usually expressed in g/cm3 for a solid and g / mL for liquids.

27. In what three states of matter does water exist ? The process of changing from one state of matter to another is called a phase change.

28. What did we learn about the freezing point of sea water compared to the freezing point of fresh water? Fresh water freezes at 0* Celsius Seawater typically freezes at -2* Celsius

29. Why did we use dry ice to test for the freezing point? Because dry ice is way colder than regular ice! It changes directly from a solid to a gas when heated above -78*C. This process is known as sublimation. What is dry ice? Solid CO 2

30. How does the boiling point of fresh water compare to the boiling point of sea water? Fresh water boils at 100* C Sea water boils at a higher temp. , typically 102* C or more.

31. Phase change diagram showing water's state of matter

32. What is buoyancy? The upward force that keeps materials afloat in fluids. The principle of buoyancy states that an object immersed in a gas or liquid is buoyed up by a force equal to the weight of the gas or liquid displaced.

33. The buoyant force is what pushes upward on objects in water. This force opposes weight, the force that pulls objects downward, toward the center of the Earth.

34. Neutral buoyancy is the ability to maintain position is the water column; not floating or sinking Example: a jellyfish

35. Osmosis – process of water moving across a membrane from areas of high water concentration to areas of low water concentration.

36. Osmoregulation = balancing the amount of water that enters or leaves cells • Necessary because shrinking or swelling of cells can be dangerous for animals. Sea turtles drink sea water but close to their eyes they have special organs called salt glands –like your tear ducts– that constantly pump the salt out of their body!

37. Osmoregulation Fresh water fish Marine fish • Freshwater fish experience the opposite problem. If it was not for osmoregulation, their cells would be constantly taking on water, like your skin cells in the bath. Instead, freshwater fish produce a lot of dilute urine, which gets rid of excess water in their systems. • Because of the process of osmosis, many bony fish in the ocean lose water to their highly saline environment. In order to stay hydrated, they drink a lot of seawater and secrete the salts through specialized cells and excrete concentrated urine.