1. Chemical and Physical Features of Seawater
Chapter 3
Chemical and Physical Features of Seawater

2. Properties of Water Low Density of Ice Temperature Moderation
Dissolves Substances
Cohesion and Adhesion*

3. Low Density of Ice
As temperature rises, hydrogen bonds break and evaporate
Seawater
Fresh water
Colder = denser until frozen
Cold water sinks
Colder = denser only to 4°C
Below 4°C = less dense

4. Heat and Water
In ice, hydrogen bonds must be broken before molecules can move around
No hydrogen bonds = melt at -90°C (-130F)
Latent heat of melting: the amount of heat required to melt
Higher than any common substance
Heat capacity: amount of heat needed to raise temperature by a certain amount
Latent heat of evaporation: the amount of heat required to evaporate
Evaporative cooling: fastest molecules leave liquid
*Water does not change temp easily.

5. Water as a Solvent Universal solvent Dissolves salts well
Salt ions are attracted to polar water molecules
Ability to transport minerals easily

6. Seawater
Volcanoes: gases released into atmosphere and then into water as precipitation
Substances come from various sources
Weathering: chemical breakdown from rocks into rivers
Hydrothermal vents: minerals from Earth’s interior

7. Seawater Salt Composition
Only 6 ions compose over 99% of solids dissolved in seawater
85% = Sodium and Chlorine
Salinity: total amount of salt dissolved in seawater
# grams left when 1,000g evaporated
psu = practical salinity units
Average = 35 0/00
Open ocean =33 to 37
Red Sea = 40 0/00
Baltic Sea surface = 7 0/00

8. Composition of Seawater
Rule of constant proportions: relative amounts of the various ions ins seawater are always the same
Salinity can change

9. Salinity, Temperature, Density
Saltier/colder= denser
Salt water freezes at lower temps than fresh
Density is controlled more by temperature
Temp varies

10. Dissolved Gases Oxygen Carbon dioxide Nitrogen
0 – 8 mL dissolved per L of seawater
Avg= 4-6 ml/l
Air = 210 mL
Carbon dioxide
80% of dis gases
Nitrogen
Gases dissolve better in cold water

11. Transparency Sunlight needs to penetrate
Clear water most transparent to BLUE
Most colors get filtered out

12. Pressure Land = 1 atmosphere (14.7 psi) Water Each 10m of depth =1 ATM
Pressure increase = gases compress
Air bladders shrink

13. “The Bends”: Decompression Sickness

14. Ocean Circulation

15. Surface Circulation Most intense ocean currents are near the surface
Driven by the wind
Influenced by the Coriolis Effect

16. Coriolis Effect
Anything that moves over the earth’s surface tends to turn instead of moving in a straight line
Earth is round and rotating
Important for wind and ocean currents
Northern hemisphere = deflects to the right
Southern = left

17. Wind Patterns Trade winds: near equator Westerlies: middle latitudes
Blow west
Westerlies: middle latitudes
Blow east
Polar easterlies: high latitudes
Driven by heat energy from the sun
Equator: heated air is less dense and rises
Air gets sucked in areas to replace rising air = wind

18. Surface Currents Driven by wind Moves in a 45° angle Ekman Spiral:
Top layer pushes on bottom
Moves at a 45° angle again
Each layer looses speed
Ekman Layer: layer affected by wind
Water moves at a 90° angle from wind

19. Movement of Warm Currents
Equitorial currents: move parallel to equator
Result of trade winds moved toward equator
Create gyres: circular systems of current
Warm water moves away from equator; cooler water moves toward it
El Niño: large-scale fluctuation

20. Currents Affect Surface Temp
Eastern coasts are usually warmer
Western = cooler

21. Layers of the Ocean
Densest water sinks, least dense toward the surface
Stratified : layers
Surface layer
100 to 200m thick
Mixed layer: wind, waves, currents
Thermocline: sudden changes in temp
Intermediate Layer
1,000 to 1,500m
Main Thermocline
Only open ocean
Deep and Bottom Layers
Below 1,500m (5,000 ft)
Less than 4°C

22. Thermohaline Circulation
Form of circulation driven by changes in density
Determined by temp and salinity
Circulation over great distances

23. The Great Ocean Conveyor
Global thermohaline circulation
Rise and fall of water throughout oceans
4,000 years
Critical in regulating climate
Brings oxygen to deep sea

24. Waves and Tides

25. Waves Caused by wind Crest: highest part Trough: lowest part
Height = distance between wave and trough
Wavelength: distance between waves
Period: time it takes for a wave to go by at one point

26. Wave Movement Water particles move in circles
Not transported
Fetch: span of open water over which the wind blows
Contributes to wave size
Swells: smoothly rounded crests
waves move away faster than the wind is blowing

27. Surf Surf: waves fall forward and break
Happens as the water becomes shallower
Waves behind catch up
Rogue waves: crests of two waves collide

28. Tides Rising and falling of sea surface Expose/submerge shore life
Drive circulation of bays and estuaries
Trigger spawning

29. Cause of Tides Gravitational pull of moon and sun
Moon’s pull is strongest on the closest side of the earth

30. Daily Tides 2 High and 2 Low tides per day
Bulges are on opposite sides of the earth at one point in the day
Full tidal cycle is 24 Hours and 50 minutes

31. Monthly Tides Sun’s affect on tides is only ½ of moon’s
Spring Tides: Tidal range increases
Full and new moons: sun and moon are in line and their affects add together
Nothing to do with season
Neap tides: tidal range is small
First and 3rd quarters

32. Variance on Earth Not all places are the same
Semidiurnal tides: 2 high and 2 low tides a day
East coast, most of Europe and Africa
Mixed Semidiurnal: higher 2nd tide of the day
West coast
Diurnal: 1 high and 1 low tide per day
Uncommon
Antarctica, parts of Gulf of Mexico, Caribbean, Pacific