Chapter 5 Water and Seawater Essentials of Oceanography 7 th Edition
Mar 29, 2015
Chapter 5 Water and Seawater
Essentials of Oceanography
7th Edition
Atomic structure
Atoms are the building blocks of all matter
Nucleus contains:Neutrons (no charge)
Protons (+ charge)
Outer shell(s) contain:Electrons (– charge) Figure 5-1
The water molecule
Composed of 1 oxygen and 2 hydrogen atoms (H20)
Contains strong (covalent) bonds between atoms
Unusual bend in geometry
Has polarity (oppositely charged ends)
Figure 5-2a
Interconnections of water molecules
Polarity causes water molecules to form weak (hydrogen) bonds between water molecules
Water sticks to itself and to other substances
Allows water to be the universal solvent Figure 5-3
Water as a solvent
Water dissolves table salt (NaCl) by attracting oppositely charged particles
Pulls particles out of NaCl structure to dissolve it
Figure 5-4
Water in the 3 states of matter
Latent (hidden) heat = energy that is either absorbed or released as water changes state
Figure 5-5
The ocean moderates coastal temperatures
Water has high heat capacity, so it can absorb (or release) large quantities of heat without changing temperatureModerates coastal temperatures Figure 5-6
Hydrogen bonds in H2O
Figure 5-8
The formation of ice
As water cools to 4°C:Molecules slowWater contractsDensity increases
Below 4°C:Hydrogen bonds formWater expands
As water freezes:Expands by 9%
Figure 5-11
Snowflake geometry
All snowflakes have 6-sided geometryCaused by water’s polarity and ability to form hydrogen bonds
Figure 5-12
Salinity
Salinity = total amount of solid material dissolved in water
Can be determined by measuring water conductivity
Typically expressed in parts per thousand (‰)
Figure 5-15
Constituents of ocean salinity
Average seawater salinity = 35‰Main constituents of ocean salinity:
Chloride (Cl–)Sodium (Na+)
Sulfate (SO42–)
Magnesium (Mg2+)Figure 5-13
Salinity variations
Location/type Salinity
Normal open ocean 33-38‰
Baltic Sea 10‰ (brackish)
Red Sea 42‰ (hypersaline)
Great Salt Lake 280‰
Dead Sea 330‰
Tap water 0.8‰ or less
Premium bottled water 0.3‰
Ocean buffering
Ocean pH = 8.1 (slightly basic)
Buffering protects the ocean from experiencing large pH changes
Figure 5-18
Processes affecting seawater salinity
Processes that decrease seawater salinity:PrecipitationRunoffIcebergs meltingSea ice melting
Processes that increase seawater salinity:Sea ice formingEvaporation
The hydrologic cycle
Figure 5-19
Surface salinity variation
Pattern of surface salinity:
Lowest in high latitudesHighest in the tropicsDips at the Equator
Surface processes help explain pattern
Figure 5-20
Surface salinity variation
High latitudes have low surface salinityHigh precipitation and runoff
Low evaporation
Tropics have high surface salinityHigh evaporation
Low precipitation
Equator has a dip in surface salinityHigh precipitation partially offsets high evaporation
Global surface salinity
Figure 5-21
Salinity variation with depth
Curves for high and low latitudes begin at different surface salinitiesHalocline = layer of rapidly changing salinityAt depth, salinity is uniform Figure 5-22
Seawater density
Factors affecting seawater density:Temperature ↑, Density ↓ (inverse relationship)
Salinity ↑, Density ↑
Pressure ↑, Density ↑
Temperature has the greatest influence on surface seawater density
Density and temperature variations with depth
Figure 5-24
Pycnocline and thermocline
Pycnocline = layer of rapidly changing density
Thermocline = layer of rapidly changing temperature
Present only in low latitude regions
Barrier to vertical mixing of water and migration of marine life
Ocean layering based on density
Mixed surface layer (surface to 300 meters)Low density; well mixed by waves, currents, tides
Upper water (300 to 1000 meters)Intermediate density water containing thermocline, pycnocline, and halocline (if present)
Deep water (below 1000 meters)Cold, high density water involved in deep current movement
Seawater desalination
Desalination methods:
DistillationSolar
Heat
Electrolysis
Reverse osmosis
Freeze separation
Figure 5-25
Distillation
Reverse Osmosis
Figure 5-26
End of Chapter 5
Essentials of Oceanography
7th Edition