The Salty Ocean

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The Salty Ocean
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The ocean contains more than water
San Jose
Salt Pans
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1) What is a salt?
2) Where do salts come from?
3) What else is in seawater?
4) Why should you care?
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A salt is a compound (two or more elements) that
has been pulled apart into its constituents by
water.
NaCl does NOT exist in seawater,
only Na and the Cl- do.
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Why are parents like water molecules?
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Dissolution occurs when a salt is broken into
its
constituent ions.
Precipitation occurs when the constituent ions
get back together and form the salt. A solid
falls out of the solution.
Precipitation occurs when the concentration of
ions exceeds the capacity of the polar water
molecules to keep the ions apart. This is called
saturation.
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Salinity is the total quantity of dissolved
solids in water.
(usually measured in parts per hundred (per
cent), parts per thousand (), or parts per mill
ion (ppm).
(saturation for NaCl is at 25)
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Where did the salts come from?
Rivers (duh!)
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How might we find out what ions are carried in
river water?
Rivers contribute calcium (Ca2), bicarbonate
(HCO3-),
magnesium (Mg2), sodium(Na)
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But, seawater is different from river water
1) Negligible chlorine (Cl-), sulfate (SO42-)in
rivers
but oceans have lots!
2) Oceans are missing calcium, silicon, magnesium
Where did the chlorine, sulfate
come from and where did the missing calcium, sil
icon, and
magnesium go?
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Lets do the simple ones first calcium and
silicon
Plankton!
(and they make shells of silica (SiO2) and
calcium
carbonate (CaCO3)
Biological processes remove calcium
and silica from seawater. They are
nonconservative constituents.
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What about magnesium, chloride, and sulfate?
Volcanos produce gases that contain chlorine and
sulfur, and these get carried by rain into the
ocean.
But not enough!
Undersea volcanic activity at ocean ridges adds
chlorine, sulfur, carbon dioxide, hydrogen,
fluorine,
and strips out sulfate and magnesium.
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Mg2 and SO4- are stripped out by
water circulation to feed the black smokers
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back to sodium chloride
outgassing of volcanos and black smokers
erosion of continents followed by river transpor
t
Cl-
Na
NaCl
(important for preserving food, human health)
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So far, we have discussed just the major
elements. There are also minor and trace elements
that are
important to us
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Key point The ocean is in chemical equilibrium
.
This does NOT mean static, but rather steady sta
te.
ocean
Out
In
In ? Out
Result? - ion concentrations are roughly constant
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How can we determine salinity?
1. Measure all ion concentrations. Sum.
OR
2. Use Principle of Constant Proportions
and measure one ion (chlorine).
Ions occur in seawater in constant
ratios, or proportions. Total concentation
may vary but ratio does not.
This is because the ocean is in chemical
equilibrium.
Salinity 1.80655 X Chlorine concentration
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The processes here are approximately balanced.
(Hint do you think this would be a good summary
picture to study for a test? The professor has
shown it twice.)
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If In?Out, how did the ocean get salty?
At some point in the past, In Out!
So, a chemical ion comes into the
ocean from weathering or outgassing,
stays for a time in the seawater, and
then leaves via sedimentation and
organic processes.
How long does an ion remain in the seawater?
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Yup! Water evaporates each year and is returned
via precipitation and runoff.
Whoa, water is a nonconservative element?!!!
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Total amount of water in oceans
1,370,000,000 cubic kilometers (km3)
Amount of water recycled through
evaporation and precipitation
334,000 km3/year
(note book has numbers that do not work out!)
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Given that a water molecule is
recycled every 4100 years and the
age of the oceans is 4,000,000,000
years old, each molecule has been
recycled almost 1,000,000 times!
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What else is dissolved in seawater?
and both of us use this to make proteins.
nitrogen (N2)
oxygen (O2)
carbon dioxide (O2)
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Nitrogen, oxygen,and carbon dioxide
are the principal gases in the atmosphere,
but proportions in water and air differ
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7th grade biochemistry review
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Oxygen made by photosynthesizing plants,
used by animals, plants to respire
Carbon dioxide made by respiration,
used by plants
Nitrogen dissolved from atmosphere
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Put in notes
Dissolved carbon dioxide in the oceans
plays a KEY role in the carbon cycle
and global warming. There is far
more carbon stored in sediments
and dissolved in the water than is
present in all life on Earth.
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BUT.60 times more CO2 in oceans
than in atmosphere.
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so it might be important to look
at the behavior of carbon dioxide
in the oceans..
CO2 from atmosphere -- ocean FAST
CO2 from ocean -- atmosphere SLOW
Oceans tend to act as a SINK for
atmospheric carbon dioxide
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CO2 is actually stored in the ocean
as carbonic acid (H2CO3), the bicarbonate ion (HC
O3-), and the
carbonate ion (CO32-).
To understand this, we must first talk
about pH ( concentration of H in
water), acids, and bases.
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Acids give up hydrogen ions (low pH)
Bases take on hydrogen ions (high pH)
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Carbonic acid acts as a buffer
to maintain pH in the ocean.
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Last piece of carbon puzzle
Precipitation/dissolution of carbonate
sediments deep water is slightly acidic (higher
CO2 and thus carbonic acid), so carbonate sedimen
ts from plankton shells slowly dissolve, adding c
arbonate ion to deep water.
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The result is an ocean with a remarkably
stable pH
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Why would some scientists suggest
pumping CO2 from the atmosphere
into the deep ocean as a way of getting
rid of greenhouse gases?
1. deep water is cold, so it can
absorb more CO2.
2.the ocean acts as a buffer and
adjusts its chemistry to accommodate
more or less CO2.
3. the oceans hold much more CO2 than does the a
tmosphere.
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