Materi kuliah tentang sifat kimia air laut

1. Ocean Chemistry
Fe2+
NO3
-Ca2+

2. • Foundations of Chemical Oceanography
– Joseph Gay-Lussay (1778-1850)
• Introduces the idea of the “WATER Column”
– Denotes depth-dependency of many ocean properties
» (esp. elements/minerals, e.g CaCO3 “calcite”)
ALGAE
Shells totally dissolve

3. © 2011 Pearson Education, Inc.
Water and Seawater

4. © 2011 Pearson Education, Inc.Chapter Overview
• Water has many unique thermal and dissolving
properties.
• Seawater is mostly water molecules but has dissolved
substances.
• Ocean is layered by salinity and density differences.

5. © 2011 Pearson Education, Inc.Atomic Structure
• Atoms – building blocks
of all matter
• Subatomic particles
– Protons
– Neutrons
– Electrons
• Number of protons
distinguishes chemical
elements

6. © 2011 Pearson Education, Inc.Water molecule
• Strong covalent bonds
between one hydrogen
(H) and two oxygen (O)
atoms
• Both H atoms on same
side of O atom
• Dipolar

7. • Water – It’s Unique Properties
H+
H+
H+
H+
O-
O-
--
--
- -
-
--
-
-
-
+
+
+
++ +
+
+
O
H H
: :
Electro + part attract electro – part
(Opposites attract)
H2O molecules form Hydrogen bonds with other H2O molecules. . .
(see above)  what makes water 
b/c of +/- nature of H2O = great at DISSOLVING substances
– aka UNIVERSAL SOLVENT (something that DISSOLVES)

8. • Dissolving Power of H2O
– Water ~ universal (solvent)
• What trying to dissolve, aka = solute (e.g. salt)
• When too much of solute/solvent  precipitation (e.g. sugar crystals or salt)
Anions (-) charge, e.g. Cl-
Cations (+) charge, e.g. Na+
Compounds of Opposite charge molecules =
“ionic compounds” – these dissolve best in H2O

9. • Salt, a solute, dissolves in water, a solvent
– Until a “saturation point” is reached
• Challenge Question?
• How can this be overcome?
– Increase temp. . .
» Solute dissolves

10. © 2011 Pearson Education, Inc.Hydrogen Bonding
• Polarity means small
negative charge at
O end
• Small positive charge at
H end
• Attraction between
positive and negative
ends of water molecules
to each other or other
ions

11. © 2011 Pearson Education, Inc.Hydrogen Bonding
• Hydrogen bonds are weaker than covalent bonds but
still strong enough to result in
– High water surface tension
– High solubility of chemical compounds in water
– Unusual thermal properties of water
– Unusual density of water

12. © 2011 Pearson Education, Inc.Water as Solvent
• Water molecules stick to
other polar molecules.
• Electrostatic attraction
produces ionic bond.
• Water can dissolve
almost anything.
• Hydration

13. Seawater
Seawater
• Seawater is a solution of about 96.5% water and
3.5% dissolved salts.
• The most abundant salt in seawater is sodium
chloride (NaCl).
• Most elements on Earth are present in seawater.
• Because these substances are dissolved, they
are in the form of ions (positive or negative
atoms).

15. Chemical Properties of Seawater
Salinity is a measure of the amount of
dissolved salts in seawater that is expressed as
grams of salt per kilogram of water, or parts per
thousand (ppt).
Seawater
• The total salt content of seawater is, on
average, 35 ppt, or 3.5 percent.
• Seawater also contains dissolved gases
and nutrients.

16. Chemical Properties of Seawater
Variations in Salinity
Seawater
– The actual salinities of the oceans vary from
place to place.
• Salinities may be as high as 37 ppt in subtropical
regions where rates of evaporation exceed those of
precipitation.
• Salinities are lower in equatorial regions where
precipitation is abundant.
• Salinities of 32 or 33 ppt occur in polar regions
where seawater is diluted by melting sea ice.
• The lowest salinities often occur where large rivers
empty into the oceans.

18. Chemical Properties of Seawater
Sources of Sea Salt
Seawater
– Geological evidence indicates that the salinity of
ancient seas was not much different from that of
today’s oceans.
– The proportion of magnesium in
the calcium-carbonate shells of
some marine organisms depends
on the overall salinity of the water
in which the shells form.
– Present-day shells contain about
the same proportion of magnesium
as similar shells throughout
geologic time.

19. © 2011 Pearson Education, Inc.Salinity
• Expressed in parts per thousand (ppt)
• Typical ocean salinity is 35 ppt (o/oo)

20. © 2011 Pearson Education, Inc.Seawater

21. © 2011 Pearson Education, Inc.Determining Salinity
• Evaporation
• Chemical analysis–titration
– Principle of constant proportions
– Major dissolved constituents in same proportion regardless of
total salinity
– Measure amount of halogens (Cl, Br, I, F) (chlorinity)
– Salinity = 1.80655 * Chlorinity (ppt)
• Electrical conductivity
– Salinometer

22. © 2011 Pearson Education, Inc.Pure Water vs.
Seawater

23. © 2011 Pearson Education, Inc.Salinity Variations
• Open-ocean salinity is 33–38 o/oo
• In coastal areas salinity varies more
widely.
– An influx of freshwater lowers salinity or
creates brackish conditions.
– A greater rate of evaporation raises salinity or
creates hypersaline conditions.
– Salinity may vary with seasons (dry/rain).

24. © 2011 Pearson Education, Inc.Processes Affecting
Salinity
• Decreasing salinity – adding fresh water to
ocean
– Runoff, melting icebergs, melting sea ice
– Precipitation
• Increasing salinity – removing water from
ocean
– Sea ice formation
– Evaporation

25. © 2011 Pearson Education, Inc.Processes Affecting
Salinity

26. © 2011 Pearson Education, Inc.Earth’s Water
• 97.2% in the world ocean
• 2.15% frozen in glaciers and ice caps
• 0.62% in groundwater and soil moisture
• 0.02% in streams and lakes
• 0.001% as water vapor in the atmosphere

27. © 2011 Pearson Education, Inc.Earth’s Hydrologic
Cycle

28. © 2011 Pearson Education, Inc.Residence Time
• Average length of time a substance remains dissolved
in seawater
• Ions with long residence time are in high
concentration in seawater.
• Ions with short residence time are in low
concentration in seawater.
• Steady state condition

29. © 2011 Pearson Education, Inc.
tract
Dissolve
d
Substan
ces

30. © 2011 Pearson Education, Inc.Acidity and Alkalinity
• Acid releases a hydrogen ion (H+) when dissolved in
water.
• Alkaline (or base) releases a hydroxide ion (OH-) in
water.

31. © 2011 Pearson Education, Inc.
pH Scale
• Measures hydrogen ion concentration
– Low pH value, acid
– High pH value, alkaline (basic)
– pH 7 = neutral
• Pure water

32. © 2011 Pearson Education, Inc.Carbonate Buffering
System
• Ocean pH averages 8.1 and ranges from 8.0 to 8.3.
• Buffering keeps the ocean from becoming too acidic
or too basic.
• Precipitation or dissolution of calcium carbonate,
CaCO3, buffers ocean pH.
• Oceans can absorb CO2 from the atmosphere
without much change in pH.

33. © 2011 Pearson Education, Inc.Carbonate Buffering
System

34. © 2011 Pearson Education, Inc.Surface Salinity
Variation
• High latitudes
– Low salinity
– Abundant sea ice melting, precipitation, and runoff
• Low latitudes near equator
– Low salinity
– High precipitation and runoff
• Mid latitudes
– High salinity
– Warm, dry, descending air increases evaporation

35. © 2011 Pearson Education, Inc.
Variation
by
Latitude

36. © 2011 Pearson Education, Inc.Global Salinity

37. © 2011 Pearson Education, Inc.Salinity Variation with
Depth
• Low latitudes – salinity
decreases with depth
• High latitudes – salinity
increases with depth
• Deep ocean salinity fairly
consistent globally
• Halocline – separates
ocean layers of different
salinity

38. Chemical Properties of Seawater
Sources of Sea Salt
Seawater
– The sources of sea salts has remained the
same over time.
• Chlorine and sulfur dioxide dissolve in water
and form the chlorine and sulfate ions of
seawater.
• The weathering of crustal rocks generates
most of the other abundant ions in seawater.
• These ions are then flushed into rivers and
transported to oceans.

39. Chemical Properties of Seawater
Removal of Sea Salts
Seawater
– Salts are removed from the ocean at the same
rate as they are added.
– The removal of sea salts involves several
processes.
• Some sea salts precipitate from seawater near
arid, coastal regions.
• Salty spray droplets from breaking waves are
picked up by winds and deposited inland.
• Marine organisms remove ions from seawater to
build their shells, bones, and teeth.

40. Physical Properties of Seawater
• Freshwater has a maximum density of 1.00 g/cm3.
Seawater
• Seawater is denser than freshwater because salt
ions are heavier than water molecules.
• The density of seawater ranges from about
1.02 g/cm3 to 1.03 g/cm3 depending on its salinity
and temperature.
• Because salt ions interfere with the formation of
hydrogen bonds, the freezing point of seawater
is –2°C.

41. • “Liebig’s Law of Minimum”
– What does it state?
• Growth of plants controlled by a single element
(required by plant) - but available at LOWEST rate of supply
Challenge Question
In this schematic which element would be rate limiting?

42. Recall - Periodic Table _Valence Electrons
Outer valence electrons (= e-) participates in bonding of Elements
e.g.
CO2 carbon dioxide
.. ..
O::C::O
‘‘ ‘’
Covalent bond
Sharing e- 
O=C=O
CO2
4 e- = (.)
6 e- = (.)

43. • Airborne particles and the World’s Ocean
– Aeolian (air/wind) Input
• Red clay (to sediments)
• trace elements ~Iron (Fe2+)
– Rate limiting nutrient for
plankton  algae bloom?
• With Iron comes
– increased Plankton blooms
Plankton Blooms produce
Dimethyl Sulfide (DMS)
 Cloud condensation nuceli
-Influences cloud formation
Fe2+
Fe2+
Dust from
Africa . . .
Fe2+
Fe2+
bloom
bloom
MODIS satelite

44. • Dissolved Elements of SeaWater
• The major constituents (elements of SeaWater)

45. • Dissolved Elements in SeaWater
• The major constituents (elements of SeaWater)
– Know the big 5 (conservative ~ lots)

46. Oceanographers
Use conductivity at diff. temps
To determine salinity
Throughout the oceans. . .
Salinity affects density 
Deep water - Ocean
Circulation/Currents. . .Climate
To be continued. .

47. Minor Constituents of Seawater
Minor constituents (≤0.1 mMol/ kg, very dilute see Table 6.1)
- trace elements (Iron, Silica)
- (secondary metabolites – venoms, poisons)
- Marine Natural Products
- Cone Snail- Conus magnus
- Conotoxins (ziconotide- Prialt®)
- 1000Xs more potent then Morphine!
morphine
ziconotide

48. • Biologically Important Nutrients: 2 classes:
– Macronutrients
• Nitrogen (N)
• Phosphorous (P)
• Potassium (K)
– micronutrients
• Iron (Fe)
• Silica (Si)
• Availability &
Supply of nutrients
Effect photosynth
in world ocean
More in Chap 13. . .

49. • Dissolved Organic Matter (DOM)
– Dissolved Carbon “C” from
• bacteria decomposition
• Leaky marine organisms (incontinent)
• Terrestrial sources
• Important in Carbon Cycle
• Add to Oceans Color
– Can be seen by satellite
– Helps to track/model
– Carbon Cycle Chp.14
» CO2 – climate change

50. • Dissolved Gasses - Challenge Questions
• What are Zones of decreased and no dissolved Oxygen called?
– 1) Hypoxic Zone – decreased O2 levels
– 2) Anoxic Zone – no O2 ! 
• Do gasses dissolve better with
increased or decreased temperature?
– Decreased temperature
Lots of nutrients (Missip river runoff) lead to
Algae blooms - Zoo plankton - use up all O2 –
( Big fish suffocate)

51. • Confirming your Knowledge
– What are the 5 major elemental constituents of SeaH2O?
• Cl, Na, S, Mg, Ca
• What are the Macro and micronutrients?
– N (nitrogen), P (phosphorous), K (potassium) (Macro)
– Fe, Si (micro)

52. • Sources ( provide) & Sinks (remove) Minerals etc.
– The above determine concentration of elements in SeaWater
– CONTINENTAL Weathering: A Source
• Na from Continental Weathering
• Cl- from Vents? Volcanoes? (acid rain)
– not f/ river rocks (recycled as spray-Ocean Waves

53. • Sources ( provide) & Sinks (remove) Minerals etc.
–Hydrothermal Vents: A Source & SINK
• +/- Minor source
• Consume other elements
Lead, Sulfur, Copper, Iron, Cobalt, Ag
Mostly gypsum & Zinc

54. • Residence Times of Elements
– When sources/ sinks in balance – ocean is steady state
– At steady state – can define the amt. of time
For total mass of an Element (e.g. Na) to be replaced
– aka Residence Time (how long it is in the ocean)
– Residence Time
• = mass of element present / rate of input or removal
• Na
– 1.472 x 1011 kg yr-1 tons/ year / 2 x108 tons/yr-1 Na/year = 70 million years!

55. • Final Thoughts
– Turn in Long Lab Field Trip (HW-1)
– Please do HW-2 (due July 7th)
– Wed – Final Chemical Oceanography -CO2_The Oceans
& Ocean Physics
Fe2+
NO3
-
Ca2+

56. Fig. 6.16

57. Fig. 6.17

58. Page 103

59. Fig. 6.18

60. Fig. 6.19

61. Fig. 6.20

62. Fig. 6.21

63. Fig. 6.22

64. Page 109

65. PHOTOS

66. Opener

67. Page 91

68. Fig. 6.1

69. Figure 6a

70. Fig. 6.14

71. TABLES

72. Tab. 6.1

73. Tab. 6.2

74. Tab. 6.3