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
temperature
Moderates coastal
temperatures
Figure 5-6
Hydrogen bonds in H2O
Figure 5-8
The formation of ice
As water cools to 4°C:
Molecules slow
Water contracts
Density increases
Below 4°C:
Hydrogen bonds form
Water expands
As water freezes:
Expands by 9%
Figure 5-11
Snowflake geometry
All snowflakes
have 6-sided
geometry
Caused 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
Baltic Sea
Red Sea
Great Salt Lake
Dead Sea
Tap water
Premium bottled water
33-38‰
10‰ (brackish)
42‰ (hypersaline)
280‰
330‰
0.8‰ or less
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:
Precipitation
Runoff
Icebergs melting
Sea ice melting
Processes that increase seawater salinity:
Sea ice forming
Evaporation
The hydrologic cycle
Figure 5-19
Surface salinity variation
Pattern of surface
salinity:
Lowest in high
latitudes
Highest in the
tropics
Dips at the Equator
Surface processes
help explain pattern
Figure 5-20
Surface salinity variation
High latitudes have low surface salinity
High precipitation and runoff
Low evaporation
Tropics have high surface salinity
High evaporation
Low precipitation
Equator has a dip in surface salinity
High 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
salinities
Halocline = layer of
rapidly changing
salinity
At 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
Distillation
Desalination
methods:
Figure 5-25
Distillation
Solar
Heat
Electrolysis
Reverse osmosis
Freeze separation
Reverse
Osmosis
Figure 5-26
End of Chapter 5
Essentials of Oceanography
7th Edition