Download Lecture 3

Chemical
and
Physical Features
of
Seawater
and the
World Ocean
“Water, water everywhere…and nor a drop to
drink!” -from Rime of the Ancient Mariner by Samuel Taylor Coleridge (1798)
• We discussed that much of our water is not
drinkable due to elevated salinity and impurities
Only 1 part in 10,000 of water is easily accessible for
drinking and irrigation.
• However, between 85-95% of many organisms
are comprised of mostly water.
• We will discuss what water is and how it’s
composition influences the marine environment,
animals in it, and humans.
Freshwater
• Water that is relatively pure, with very few
dissolved salts
• Freshwater occurs in:
• Lakes, rivers, streams, groundwater, glaciers,
rainwater, soil, water vapor in the atmosphere
(In contrast, ocean water is salty because salts from land
run into it and stay there as surface water evaporates.)
Water: Unique Properties
• We know that water
consists of two atoms of
hydrogen and one atom
of oxygen (H2O)
• Water molecules are
held together by electrochemical hydrogen
bonds (fairly weak)
Freshwater
• Only 2.5% of the planet’s water is freshwater, and only
1% of that exists on Earth’s surface.
Figure 14.1
•Water, ice, and vapor exist
on earth.
•In a special instance you
can see them all at once.
•Try an ice cube on the
counter on a hot summer day!
Hydrogen bonding permits water to change
phase when energy is added or taken away.
Water: The Universal Solvent
• Water dissolve many
things and is known as
the universal solvent,
esp. salts.
• Again, H+ bonding plays
a role hear by interacting
with other charged
atoms.
• The oceans
consist of (by
mass):
• 96.5% water
• 3.0% sodium
and chlorine
ions (table salt,
Na+ and Cl–)
• 0.5% other salts
Figure 13.3
How does seawater get this way??
• Coastal waves, rain,
and other sources of
weathering erode rocks
and move sediments
into the ocean.
• Other sources of
minerals include
hydrothermal vents and
even aquaculture!
Tridacnid clam: James Fatherree
Salinity
• All in all the total amount of salt dissolved in
seawater, or salinity, is about 35 ppt.
• The concentrations of individual salts don’t vary
much either, due to the rule of constant
proportions*.
• Therefore, even if marine organisms are
exposed to changes in total salinity, the changes
in individual ion concentration remains similar.
*R.C.P.: Relative amounts of the various ions in seawater are always the same.
Scientists use Niskin bottles and “messengers” to sample
water at depth.
• Water density varies with salinity and temperature.
• If salinity or temperature increase, so does the density of the water.
Need more samples...
No problem.
“Rosettes,” or multiple sampling
arrays may be deployed to take
measurements at multiple depths..
Alternatively, different tools may
be attached to the sample array
providing a multitude of readings
to be made in a single drop!
Hey, it beats doing it by hand!
• Dissolved gasses such as
CO2 and N2 can be measured
in addition to O2.
Of course, if you have LOTS of cash, the satalites have come a long way.
Seawater also does other cool stuff!
Light transmission
-loose color at depth
Pressure
-increases 1 atmosphere for
each 10 m increment
OUCH!
Part II: Ocean Circulation
Water Motion and the Earth
• The ocean never truly stops moving.
Just ask Russell Crowe!
• Much of the circulation we might experience
actually occurs at the surface.
• Wind drives much of the “ocean motion,” but
something else plays a role, earth’s rotation.
• This is known as the Coriolis Effect.
Bench view
Your view
Homeland
Security’s View!
Another point of view…
Notice that no matter what
direction you are turning,
the “deflective” force is
still clockwise in the North
and counter-clockwise in
the South!
Wind Patterns
Wind Patterns
• Ultimately, the power of the wind evolves from
the sun and it’s affect on the air temperature.
• Hot air rises because it is less dense and vice
versa.
• As air moves up (or out of the way) other air
rushes inward to occupy the existing “space”
• Air is bent by the Coriolis Effect just like water,
therefore…
Convection cells
created by rising
and sinking air
are responsible for
much of our sailing
history.
Surface Currents
• All major surface currents are driven by the wind.
• Again, Coriolis Effect causes the surface waters to track
toward the right (N. hemisphere).
• Progressive spiraling caused
by shallower currents pushing
on deeper currents results
in Ekman Spirals.
• As spirals continue, wind shear
becomes less and less at depth.
• Eventually, deep currents travel
~90° to the wind direction.
The final result: formation of gyres. El Niño and
other large fluctuations can occur.
Ultimately this type of circulation affects the average temperatures
in oceans in both hemispheres.
• Since the ocean is three
dimensional most currents
are only viewed as surface
events.
• We know that dense water
sinks. Stratification takes
place during each season.
• Thermoclines may result
when mixing of upper,
intermediate and deep
layers do not mix well.
Occasionally, large changes in surface
water temperature facilitates complete
mixing of ocean depths, resulting in
overturn of the water column.
Waves and Tides
Waves, the result of surface winds, have been responsible
for many changes, some beneficial and some destructive.
Technically, the water never moves!
Surf is created as energy from the wave bunches
and changes shape near the shore.
One benefit of waves and tides.
Some waves are just plain mean!!
How do tides happen?? Gravitational forces by
the moon and the sun pulling on water cause the
rise and fall of tides.
Since the earth rotates and the moon and sun,
pull, tides occur at several intervals throughout the
day.