Chemical and
Physical Features of
Seawater
Chapter 3
Figure 3.01
The charged ends of the water molecule (hydrogen bonds) gives it
unique properties.
Water molecules
• Water is cohesive, it sticks together.
• Water is adhesive, it sticks to other
things.
• It expands when it freezes.
• Water is the universal solvent, it
dissolves most solids.
Figure 3.02
Evaporation occurs when molecules break free of hydrogen
bonds and enters the gaseous state.
WATER PHASES
Figure 3.03
Water molecules are spaced further apart when frozen,
making it less dense than liquid water. Why is that important
to a Marine Biologist?
Figure 3.05
Water the universal solvent weakens the bonds of the sodium
chloride, causing it to dissociate.
Solutes in seawater
Figure 3.06
Ions enter the ocean via weathering of rock and volcanic
activity.
Sodium and chlorine account for 85% of the solutes in seawater.
• Salinity is defined as
the amount of salt
dissolved in water.
Salinity is expressed
as the number of
grams of salt left
when 1,000 grams of
sea water is
evaporated. If 35
grams of salt remains
and 965 grams of
water evaporated, the
• When salt water freezes the ions are not included in
the ice. consequently the surrounding water
increases in salinity and the ice is all most pure
water. Salt water freezes at a colder temperature
than pure water.
Figure 3.07
This Niskin bottle is used to sample water at various depths
Figure 3.08
Thermocline is where the temperature drops rapidly as it gets deeper.
Figure 3.09a
Many collection bottles can be arranged along with other
instruments and lowered by cable. Temperature, salinity, light, water
clarity, and other data can be collected.
Figure 3.09b
Figure 3.11
Different colors of light penetrate to different depths in the ocean.
Figure 3.12
Red colors are filtered out first.
Figure 3.13
The secchi disk is a simple device used to detect water clarity.
Figure 3.14
At sea level there is 1 ATM atmosphere (14.7 psi). With each 10m or
33ft of depth another ATM of pressure is added.
Figure 3.15
This fish was brought up to fast from depth, and the swim
bladder expanded filling with air.
Figure 3.10
Satellite image shows ocean temperatures coldest is blue and warmest
in red. Why is it warmer in the middle?