Chemical Properties of
Water
The basics and a little more
than you wanted to know!
Temperature
The most important limiting
factor
Changes can alter many other
parameters (thermal pollution is
a big problem)
Surface water that is heated by
the sun goes through seasonal
changes.
The Thermocline is a narrow
band of water that separates
warm surface water from cool
bottom water
Cold water holds more oxygen
than warm water.
Sea Surface Temperatures
A little More
Evaporation and condensation provide
energy to run the hydrological cycle
This energy reduces the possibility of freezing
in marine organisms’ tissue
Water also has a high heat capacity that
allows it to absorb or release large
quantities of heat with little temperature
change
This helps in moderating climates
Salinity
The amount of dissolved solids in water
Includes ions of chloride, sodium, sulfate,
magnesium, calcium and potassium
Measured using a hydrometer to calculate
specific gravity, or by conductivity. Units
would be measured in ppt.
Surface salinity is greatly influenced by
temperature.
High temps cause increased evaporation rates
and increased salinity.
The Halocline
Like the thermocline, only it is the
zone dividing the surface
(fluctuating) salinity with the
constant salinity found in deep water.
Stenohaline organisms can not
tolerate changes in salinity
Euryhaline organisms adapt to most
fluctuations
Density
Affected by both temperature and
salinity
800x’s as dense as air.
Density causes bouyancy
Thermocline + Halocline = Pycnocline
pH – logarithmic function of the
% of hydrogen ions in a solution
In sea water, pH is between 7.5 –8.5
Closely associated w/ dissolved CO2
CO2 is a reactant in photosynthesis
and a product of respiration.
Dissolves easily in sea water and is
stored in marine shells and sediments.
H2O + CO2 = H2CO3, Lowers pH
H2CO3 = HCO3+ H, raises pH
pH cont.
Both reactions change the pH of the
water.
Ph is expressed on a scale from 1-14.
Each value is a ten fold increase over
the previous.
The pH Scale
pH Cont.
Enzyme activities and the shapes of
vital proteins require a stable pH.
A decrease in pH could dissolve the
calcium carbonate in mollusk shells.
Dissolved Gases
Dissolved N is the most common gas in the
ocean. Dissolves from the atm. where it is
78%.
N gas can’t be used by organisms until it is
attached to O in a process called nitrogen
fixation.
N fixation occurs because blue-green algae
convert N gas to a useable form that animals
need for building proteins and amino acids.
Dissolved Oxygen
primarily comes from photosynthesis of
marine plants and algae. They produce over
50% of the total atmospheric Oxygen. (not
to be confused with oxygen in the water
molecule )
O is not very soluble so most of it diffuses
into the air.
Below the thermocline, there is very little O.
Carbon Dioxide
Carbon dioxide is highly soluble in sea
water which contains about 50 x’s more
CO2 than the atmosphere.
Enters the water from air as well as through
respiration.
Can be depleted at surface by plants.
Necessary for shell formation.
Oceans remove and store CO2 which remain
relatively constant at 45-54 ml/liter of sea
water.
Transmission of Light
light in the sea comes from two sources: sun
and organisms
a large portion of the electromagnetic
radiation from sun (or moon) is reflected back
into atmosphere -- so only the upper
kilometers of the water column are illuminated
Seeing the Light
light below the surface differs from that above in
both quality and quantity because a major change
occurs at the air-sea surface interface
combined consequences of reflection from the
surface and refraction into it reduce the
angular distribution of light to a narrow cone of
solid angle 97°
so a fish looking upward only sees the surface
above water in that cone -- or window (called
Snell's window) -- outside of the window is backscattered light from deeper water
Light Penetration
water absorption preferentially removes
both long (red) and short (ultraviolet)
wavelengths, rapidly resulting in nearmonochromatic blue light, which is then
reduced by 90% for every 70 m of depth
in coastal waters material from plant decay can
absorb additional short wavelengths, resulting
in a greenish hue to the water
turbidity allows green wavelengths to penetrate
Penetrating Light
since water selectively absorbs the reds and violets, blue
penetrates to the lower limits of the photic zone
(autotrophs use red and blue wavelengths) before being
absorbed
the intensity of light decreases with greater depth
thus autotrophs are restricted to the illuminated upper
surfaces of the ocean, called the photic zone and are unable to
live in the dark lower portion of the ocean called the aphotic
zone
colors are seen differently in shallow vs. open ocean water:
in shallow water there is a structural background of the
shore or a reef which allows animals to hide in it; in open
ocean, no refuge exists and the background is uniform
Light Cont.
Marine Plants (autotrophs) make their own
food by photosynthesis. Heterotrophs can’t
make food so they eat plants.
The cycle depends on light entering the
water which may be absorbed or reflected.
About 65% of light energy is absorbed in the
first 5 feet and can’t be used by autotrophs.
More Light
Red light is absorbed first in most marine
environments. Many marine bottom dwelling
animals are red. Why?
Blue is transmitted best
Light is inversely proportinal to depth. As
you descend, it gets darker.
The lighted layer is called the photic zone:
about 10% of the ocean.
The dark layer is the aphotic zone.
Turbidity
Turbidity is a measure of the suspended
sediments.
More sediments results in less light
penetration and poor visibility.
Photosynthesis is reduced.
The compensation zone is the depth where
the rate of photosynthesis = rate of
respiration.
O production = rate of respiration
Turbidity cont.
Turbidity can be measured
with a secchi disk as
visibility.Divide the depth
of the secchi line by the
water’s depth.
Turbidity is lower in areas
of high productivity.
Pressure
Pressure at sea level is the weight of
air (14.7 psi)
As you descend, pressure results
from the weight of the water above
you (hydrostatic pressure) as well as
air pressure.
Pressure going down
For every 33 feet = 1 atm of pressure
At 100 feet = 4 atm of pressure or
~58.8 psi
The pressure at the Mariana Trench
is ~ 7 tons/in2
Increased pressure lowers water’s
freezing point without affecting the
volume.
More on Pressure
SCUBA tanks contain air under pressure so
that the internal pressure inside the lungs
equals the pressure on the external
surfaces exerted by water
When ascending, the air volume in your
lungs expands. The lungs could be ruptured
if you do not continuously exhale.
There is a limit to how much pressure a
person can with stand. It varies due to
experience but safe, recreational diving
stops at 130 feet.
Molecular arrangement of water
The shape of the water molecule gives it
special properties that effect marine
organisms.
Viscosity is the resistance to flow: it provides
buoyancy for plankton while increasing the
energy used by nekton to swim.
Surface tension is the attraction of surface
water molecules.
Water is the universal solvent.
Relationships of Parameters
Properties of water are
interconnected. Their relationship to
each other demonstrates how easily
the delicate balance can be disturbed.
Direct relationship = Two parameters
both increase or decrease at the same
time
Inverse relationship = one parameter
increase, while the other decreases.
In General
As you descend, the ocean becomes
colder, denser, saltier, has more
pressure, less light and has fewer
gases.