MAR 110: Introductory Oceanography

1. MAR 110: Introductory Oceanography Properties of ocean water

2. Salt and history, part 1 • The ancient city of Jericho – one of the oldest surviving settlements in human history – is located on the Dead Sea. • The city was apparently founded as a salt trading center, and the Dead Sea has long been a source of salt. • The Dead sea is in a depression along a transform fault complex originating in the Gulf of Aqaba. • The salt of the Dead Sea originated in an arm of the Mediterranean Sea that was cut off by tectonic movements about 6 million years ago. • In time, most of the water evaporated and left the salt behind. Properties of ocean water

3. Salt and history, part 2 • Salt has long been important to humans as a preservative and spice; at times in human history, salt was as valuable as gold, if not more so. • Besides its use as a preservative and seasoning, salt is used to clear roads and walkways, in manufacturing, and as water softeners to remove other dissolved substances during water treatment. • Salt is typically obtained either by evaporation processes or by solution mining of rock salt. Properties of ocean water

4. Water and life • Water is essential for life as we know it. • Astronomers search for water on distant planets in the effort to find life elsewhere in the universe. • Life on Earth began in water and evolved there for 3 billion years before spreading onto land. • Terrestrial organisms are tied to water, too. • Most cells are surrounded by water and cells are about 70-95 percent water. • Water exists in three states: ice, liquid, and vapor. Properties of ocean water

5. Water is a polar molecule • The chemical formula of water is H2O. • Water is a polar molecule because oxygen has a much higher affinity for electrons (is more electronegative) than hydrogen. • Because oxygen is more electronegative, the electrons spend more time around the oxygen, giving the oxygen end of the molecule a partial negative charge. • The hydrogen end of the molecule likewise has a partial positive charge. • Thus, opposite ends of the water molecule have opposite charges; such molecules are called polar molecules. Properties of ocean water

6. Properties of ocean water

7. Hydrogen bonds, part 1 • The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond. • Each water molecule can form hydrogen bonds with up to four neighbors. Properties of ocean water

8. Hydrogen bonds, part 2 • The hydrogen bonds joining water molecules are weak, about one-twentieth as strong as covalent bonds (which involve electron sharing between atoms). • They form, break, and reform with great frequency. • At any instant, a substantial percentage of all water molecules are bonded to their neighbors, creating a high level of structure. Properties of ocean water

9. Unusual properties of water • Water’s high polarity and ability to form hydrogen bonds gives the molecule peculiar properties: • Cohesion (and adhesion); • Unique thermal properties that make water resistant to temperature change (and change of state); • Highest density in liquid state; and • A versatile solvent. Properties of ocean water

10. Cohesion • Hydrogen bonds hold water molecules together; this ability to stick together is called cohesion. • Cohesion makes it possible to transport water against force of gravity. • A related property, adhesion – the ability to stick to another polar or charged substance like glass or xylem vessels – likewise makes it possible to transport water against force of gravity. • Cohesion between water molecules creates high surface tension makes it difficult to break surface. Properties of ocean water

11. Kinetic energy • Kinetic energy is the energy of motion. • Heat is the total quantity of kinetic energy in a substance. • Temperature is the average amount of kinetic energy in a substance. Properties of ocean water

12. Measuring heat • Kinetic energy often measured in calories (cal), the amount of heat energy required to raise the temperature of 1 g of water 1 °C • The joule (J) is another way to measure kinetic energy. • 1 cal = 4.187 J; 1 J = 0.239 cal. • The British Thermal Unit (BTU) is the amount of energy it takes to raise the temperature of 1 pound of water 1 °F (from 62°F to 63°F). • 1 BTU = 252 cal = 1055 J Properties of ocean water

13. Measuring temperature, part 1 • There are a number of instruments for measuring temperature. All work on the principle that most substances expand when heated, calibrating this change in volume to measure temperature. • There are three temperature scales used in the United States: the Fahrenheit Scale, the Celsius Scale, and the Kelvin Scale. • The Fahrenheit scale is used by public weather reports from the National Weather Service and the news media; few other countries than United States use it. Properties of ocean water

14. Measuring temperature, part 2 • Three temperature scales (continued): • The Celsius scale is used either exclusively or predominately in most countries other than United States, which uses it for scientific work. It is slowly being established to supersede the Fahrenheit scale. • 0 °C = 32 °F • 100 °C = 212 °F • The Kelvin scale is used in scientific research, but not by climatologists and meteorologists. It is similar to the Celsius scale, but the zero point is set to absolute zero, the temperature at which all molecular motion ceases. • 0 K = -273.15 °C = -459.67 °F Properties of ocean water

15. Properties of ocean water

16. Unique thermal properties, part 1 • Based on its molecular weight and the properties of similar substances, pure water should freeze at -90 °C and boil at about -70°C. • Instead, pure water freezes at 0°C and boils at 100°C. • The unique thermal properties are a result of water’s structure, and its tendency to form hydrogen bonds. Properties of ocean water

17. Latent heat, part 1 • Latent heat is energy used to change the state of water rather than change the temperature, thus it is latent, or hidden. • When water is at a temperature at which it should change state, latent heat is added or removed until the change of state is complete; the temperature, however, does not change. • Latent heat of fusion is the hidden heat given off or absorbed as water freezes or melts. • The latent heat of fusion of water is 80 cal/g at 0 °C. Properties of ocean water

18. Latent heat, part 2 • Latent heat of vaporization is the amount of energy it takes for 1 g of a substance evaporates. • Latent heat of condensation is the amount of energy given off as 1 g of a substance condenses. • The latent heat of vaporization/condensation of water varies with temperature, ranging from 597 cal/g at 0 °C to 540 cal/g at 100 °C. Properties of ocean water

19. Latent heat, part 3 • Latent heat of sublimation is the amount of energy it takes for 1 g of a substance changes directly from the solid state to the gaseous state. • Latent heat of deposition is the amount of energy given off as 1 g of a substance changes directly from the gaseous state to the solid state. • The latent heat of sublimation/deposition of water is relatively constant, ranging from 677 cal/g at 0 °C to 678 cal/g at -30 °C. Properties of ocean water

20. Properties of ocean water

21. Specific heat • Specific heat is the amount of energy it takes to raise or lower the temperature of 1 g of a substance 1 degree C. • The specific heat of water is 1 cal/g/°C. • The specific heat of ice is 0.5 cal/g/°C. • Water changes its temperature less than most other substances when it absorbs or radiates a given amount of energy. Properties of ocean water

22. Properties of ocean water

23. Properties of ocean water

24. Climate effects • Water’s thermal properties explains its thermal inertia, or its resistance to temperature change when it absorbs or radiates a given amount of energy. • Water stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air. • Water can absorb or release relatively large amounts of heat with only a slight change in its own temperature. • In turn, water’s thermodynamic properties explain why maritime climates have more moderate temperature ranges than arid climates, and why sweating is so important to cooling the body. Properties of ocean water

25. Evaporative cooling • The evaporation of water removes a lot of kinetic energy from the body, thus bringing the temperature down. • When a person becomes dehydrated, this cooling mechanism breaks down. • This is why it is important to drink plenty of liquids during hot weather, intense exercise or while sick. Properties of ocean water

26. Solutions • A solution is a liquid that is a homogenous mixture of two or more substances. • The solvent is the dissolving agent. • The solute is the substance being dissolved. • An aqueous solutions is one in which water is the solvent. Properties of ocean water

27. Versatile solvent • Pure water rarely occurs naturally, as water typically contains a variety of dissolved and suspended substances. • Water’s polar properties make it a good solvent for polar and ionic compounds. • The negatively charged oxygens attract positively charged ions or poles, while the positively charged hydrogens attract negatively charged ions or poles. • Polar molecules are also soluble in water because they can also form hydrogen bonds with water. • Even large molecules, like proteins, can dissolve in water if they have ionic and polar regions. Properties of ocean water

28. Example of a solution • When a crystal of salt (NaCl) is placed in water, the Na+ cations form hydrogen bonds with partial negative oxygen regions of water molecules. • The Cl- anions form hydrogen bonds with the partial positive hydrogen regions of water molecules. • Each dissolved ion is surrounded by a sphere of water molecules, a hydration shell. • Eventually, water dissolves all the ions, resulting in a solution with two solutes, sodium and chloride. Properties of ocean water

29. Properties of ocean water

30. Chemistry of seawater, part 1 • The constituents of seawater comes from several sources: • Weathering and erosion of rock on land and transport by rivers to the oceans; • Volcanic activity, such as at hydrothermal vents; • Removal via sedimentation, subduction and other geological processes; • Solution of gases from the atmosphere. Properties of ocean water

31. Chemistry of seawater, part 2 • Seawater is a salt solution of nearly uniform composition. • Salinity is a measure of the amount of salt dissolved in seawater. • The salinity of seawater averages about 3.5 percent. • If all the water in the oceans evaporated, sea salts would cover the Earth to a depth of 45.5 m. Properties of ocean water

32. Chemistry of seawater, part 3 • William Dittmar, analyzing water samples from the Challenger expedition, confirmed earlier observations that the ratio of the concentrations of the major constituents of seawater was similar. • Dittmar thus discovered the principle of constant proportions, which allows one to estimate total salinity of seawater based on a measurement of the concentration of one ion, such as chloride (Cl-). Properties of ocean water

33. Chemistry of seawater, part 4 • The concentration of seawater constituents such as chloride and sodium (Na+) occur in constant proportions and change slowly by mixing; thus they are conservative properties of seawater. • The concentrations of other constituents are more variable; thus they are non-conservative properties of seawater. Properties of ocean water

34. Chemistry of seawater, part 5 • The salinity of seawater was originally measured by a titration method, but after World War II scientists observed that measurments of the electrical conductivity of seawater can provide much more accurate measurements. • Salinity is now determined from the ratio of the conductivity of a water sample to that of standard seawater; it is given in practical salinity units (psu). • Standard seawater is prepared by Ocean Scientific International. • Evaporation of seawater increases salinity; freshwater runoff decreases salinity. Properties of ocean water

35. Properties of ocean water

36. Chemistry of seawater, part 6 • While more than 70 minerals are dissolved in seawater, six make up more than 99 percent of all sea salts: chloride, sodium, sulfate (SO42-), magnesium (Mg2+), calcium (Ca2+), and potassium (K+). • Table salt (NaCl) makes up more than 86 percent of sea salts. • Important trace elements include aluminum (Al), chromium (Cr), gold (Au), lead (Pb), nickel (Ni), and zinc (Zn). Properties of ocean water

37. Properties of ocean water

38. Chemistry of seawater, part 7 • Gases, such a carbon dioxide (CO2), nitrogen (N2), and oxygen (O2), also dissolve in water. • The solubility of gases in water is typically inversely correlated with temperature. • In seawater, salinity and pressure also affect the solubility of gases, but temperature is the major driver. • Waves on the surface encourage solution of gases by increasing the roughness and surface area of the water, thus increasing the interface between atmosphere and ocean. Properties of ocean water

39. Properties of ocean water

40. Chemistry of seawater, part 8 • Biochemical processes also affect the concentrations dissolved gases in seawater. • In the photic zone (defined by the depth to which light penetrates), photosynthesis removes carbon dioxide and adds oxygen. • In the aphotic zone (below the depth to which light penetrates), no photosynthesis is possible; decomposers predominate; the process of cellular respiration removes oxygen and adds carbon dioxide. • Carbon dioxide is more abundant in the ocean than the atmosphere. Properties of ocean water

41. Chemistry of seawater, part 9 • Gases not involved in biochemical processes remain at a relatively constant concentration; any changes in concentration typically result from diffusion of the gases. Properties of ocean water

42. Dissociation, part 1 • Occasionally, a hydrogen atom shared by two water molecules shifts from one molecule to the other. • The hydrogen atom leaves its electron behind and is transferred as a single proton - a hydrogen ion (H+). • The water molecule that lost a proton is now a hydroxide ion (OH-). • The water molecule with the extra proton is a hydronium ion (H3O+). Properties of ocean water

43. Dissociation, part 2 • A simpler way to view this process is that a water molecule dissociates into a hydrogen ion and a hydroxide ion: • H2O <=> H+ + OH- • This reaction is reversible. • In pure water at equilibrium, only one water molecule in every 554 million is dissociated. • At equilibrium the concentration of H+ or OH- is 10-7M (25 degrees C). Properties of ocean water

44. Dissociation, part 3 • Because hydrogen and hydroxide ions are very reactive, changes in their concentrations can drastically affect the proteins and other molecules of a cell. Properties of ocean water

45. Acids and bases, part 1 • Adding certain solutes, called acids and bases, disrupts the equilibrium and modifies the concentrations of hydrogen and hydroxide ions. • An acid is a substance that increases the hydrogen ion concentration in a solution. • Any substance that reduces the hydrogen ion concentration in a solution is a base. • Some bases reduce H+ directly by accepting hydrogen ions. Properties of ocean water

46. Acids and bases, part 2 • Other bases reduce H+ indirectly by dissociating to OH- that combines with H+ to form water. • Strong acids or bases dissociate completely in water. • In weak acids or bases, the dissociation is reversible; at equilibrium there will be a fixed ratio of products and reactants. Properties of ocean water

47. Example reactions • HCl => H+ + Cl- • NaOH => Na+ + OH- • NH3 + H+ <=> NH4+ • H2CO3 <=> HCO3- + H+ Properties of ocean water

48. The pH scale • In any solution the product of their H+ and OH- concentrations is constant: • [H+] [OH-] = 10-14. • The pH is the negative logarithm of the hydrogen ion concentration, and can range from 1 (very strong acid) to 14 (very strong base) • Neutral pH is 7. • Most biological fluids range from pH 6 to pH 8. Properties of ocean water

49. Properties of ocean water

50. Buffers • Buffers minimize changes in pH by accepting hydrogen ions from the solution when they are in excess and donating hydrogen ions when they have been depleted. • Buffers typically consist of a weak acid and its corresponding base. • Carbonic acid (H2CO3) serves as an important buffer in biological systems. Properties of ocean water