The Physical and Chemical
Properties of the Ocean
Physical Properties of Water
Light
• Sunlight is absorbed as it enters
the ocean.
• All colors of light are given off by
the sun.
• Red is the 1st color to be
absorbed
• Blue light is the last color
absorbed and penetrates the
furthest.
Physical Properties of Water
Why are many small prey
organisms red?
• A red organism appears red
because it reflects red light.
• Red light does not penetrate
more than 10 meters.
• Since there is no red light to
reflect, a red organism would
appear black below 10 meters.
Physical Properties of Water
Temperature
• As you dive deeper in the ocean
the temperature decreases.
• Thermocline: the layer of water
that shows a large amount of
temperature change with depth.
– Above the thermocline: The
surface water is heated by
the sun.
– Below the thermocline:
There deep water is uniformly
cold.
Physical Properties of Water
Pressure
• As you dive deeper in the ocean
the pressure increases.
• For every 10 meters you dive into
the ocean the pressure increases
by 14.7 psi. (1 ATM)
– Diving deeper into the ocean
Increases pressure and causes
the gases in the organism’s
body to compress.
– Rising to the ocean surface
decreases pressure and causes
the gases in the organism’s
body to expand.
Physical Properties of Water
Sound
• Sound travels further in water
than it does on land but our ears
are not designed to hear
underwater.
• Slower moving (low-pitched)
sounds travel further.
• Decreasing temperature,
decreases sound speed,
increases distance
• Increasing pressure, increases
sound speed, decreases distance
Physical Properties of Water
Sound
• SOFAR Channel: The depth of
the ocean where sound travels
the slowest and the furthest.
– Above the SOFAR channel:
Sound doesn’t travel as far
because temperature is too
high.
– Below the SOFAR channel:
Sound doesn’t travel as far
because pressure is too high.
Chemical Properties of Water
Water
• Molecular Formula: H2O
• Molecular Structure: every
molecule of water contains 1
oxygen atom and 2 hydrogen atoms.
– Each hydrogen atom is bonded to
the oxygen atoms with a covalent
bond.
– What is a covalent bond?
Chemical Properties of Water
Water is a polar molecule.
• Polar Molecule: a molecule that has
a slightly positive side and a slightly
negative end.
– There are more electrons
surrounding the oxygen atom
than the hydrogen atoms.
– Oxygen atom has a slightly
negative charge.
– Hydrogen atoms has a slightly
positive charge.
Chemical Properties of Water
• Hydrogen Bonds: A weak bond that forms between the
positive end of one water molecule and the negative end
of another water molecule.
• How is a hydrogen bond different than a covalent bond?
Properties of Water
• Adhesion: a water molecule
forms a hydrogen bond to a
surface or an object.
Chemical Properties of Water
Properties of Water
• Cohesion: a water molecule forms a hydrogen bond with
another water molecule.
– Cohesion makes water have
high surface tension – it is
difficult to break the
surface of a body of water.
– Cohesion makes water a
viscous liquid – it is difficult
to move through.
Chemical Properties of Water
Water molecules and in constant motion. The higher the
temperature the faster the molecules are moving.
The Three States of Water:
• Gas (vapor): When a water molecule moves fast enough it
breaks free of all hydrogen bonds and becomes a gas.
– Water molecules are spread much further apart than in
liquid water.
– Increasing temperature, increases the rate of evaporation.
Chemical Properties of Water
The Three States of Water:
• Liquid: Hydrogen bonds hold most of the water molecules
together in small groups.
– Hydrogen bonds are
constantly being broken and
reformed.
– Cold Water: Is more dense
because molecules move
slower and packed in tighter
causing.
– Warm Water: Is less dense
because molecules move
faster and spread out.
Chemical Properties of Water
The Three States of Water:
• Ice: when water freezes, the molecules move so slowly
that hydrogen bonding locks each molecule in place
forming a crystal.
– In ice, the water molecules
are further apart than in
liquid water.
– Ice is less dense than liquid
water.
– Why is it important that ice
floats in the ocean?
Chemical Properties of Water
Heat Capacity: The amount of energy needed to raise the
temperature of a substance.
• Water has the highest heat capacity of any natural
substance.
• Heat energy must
be used to break
hydrogen bonds
between water
molecules before
the molecules are
able to move faster
and increase
temperature.
Chemical Properties of Water
• It takes a long time and a lot of energy for water to heat up
or cool down.
• Water’s high heat capacity protects marine organisms from
drastic changes in temperature that you may experience on
land.
• A relatively constant
ocean temperature
helps marine
organisms maintain
homeostasis: an
organism’s ability to
maintain constant
and stable internal
conditions.
The pH of Ocean Water
Acid, Bases and pH
• Water molecules sometimes split apart to from ions.
• Pure water is neutral it has a equal number of
positive and negative ions
The pH of Ocean Water
•
•
•
•
Acids
Have more H+ ions
than OH- ions in
solution.
pH less than 7
The lower the
number, the stronger
the acid.
Ex: HCl is a strong
acid produced by the
stomach to digest
food.
Bases
• Produces more OHions than H+ in
solution
• pH greater than 7
• The higher the
number the stronger
the base.
• Ex: Ocean water has a
pH of 8
The pH of Ocean Water
pH: (power of Hydrogen) as in Hydrogen ions
• Measures the H+ concentration in solution: [H+]
• It is a log scale, so it increases by powers of ten.
• Ex: How many times more acid is vinegar compared to
coffee?
The pH of Ocean Water
Buffer: A solution that prevents
sharp and sudden changes in pH.
• Ocean water acts as a buffer and
resists changes in pH.
• Many land animals have buffers in
their blood that maintain a
constant pH.
• If the pH of an organism changes,
it will affect the chemical
reactions inside their cells.
• Buffers help organisms maintain
homeostasis with respect to pH.
Chemical Properties of
Saltwater
Salt: any substance that consists of
negatively charged particles
bonded to positively charged
particles.
• Table Salt (NaCl) is only one
example of a salt
– The Na atom loses an electron,
forming an ion with a positive
charge.
– The Cl atom gains an electron,
forming an ion with a negative
charge.
Chemical Properties of Saltwater
• Salt crystals dissolve in water
– The negative end of the water molecules are attracted
to the positive ions in salt.
– The positive end of the water molecules are attracted to
the negative ions in salt.
– Water molecules surround each ion and keep them
separated.
Chemical Properties of Saltwater
Salinity: the amount of salt dissolved in water
The average salinity of
the ocean is 35 ppt
(parts per thousand).
How many grams
of salt are there
in 2,000 grams of
saltwater?
Chemical Properties of Saltwater
Why is there so much salt in ocean water?
Positive ions fcome rom
weathering rock are
carried to the ocean
through streams and
rivers
Negative ions come from volcanic
eruptions and deep sea hydrothermal
vents
Chemical Properties of Saltwater
Rule of Constant Composition: the percentage of each
chemical dissolved in ocean water will always remain the
same.
– The salinity (35 ppt) changes with depth.
– The “stuff” dissolved
in the water will
always be the same.
– If you sample water
from any ocean at any
depth the % of each
chemical dissolved will
be the same.