Sea Water Chemistry, and Physical Properties of Sea Water

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Ocean water Chemistry - Salinity, Continued
2
The Components of Salinity
The most abundant components of a kilogram of
seawater.
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The Principle of Constant Proportions
Although the salinity of various samples of
seawater may vary, the ratio of major salts is
constant.
4
Question
Is the ocean becoming progressively saltier with
age? What processes might add or remove salt
from the ocean?
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Is the ocean becoming progressively saltier with
age?
Rivers contain salt which is delivered
continually to the sea Salts do not evaporate
when water evaporates
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Steady State
Is the ocean becoming progressively saltier with
age? No, the proportion and amounts of dissolved
solids remain constant. This concept is known as
the steady state ocean. Ions are being added
to and removed from the ocean at the same rate.
7
Question

• What factors control the residence times of
• water,
• ii) salts,
• iii) nutrients and
• iv) gases in the ocean?
• What are the timescales for each?

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Steady State Addition and Removal
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Definition of Residence Time
Residence Time Amount of substance in the
ocean rate of
addition or removal from ocean We usually
measure rate of addition to the ocean, because
its relatively easy to measure the contribution
of a substance via river discharge
Chloride in sea water X ocean
volume Chloride in river water Global river
discharge
Chloride in sea water 19 g/kg Chloride in river
water 6 mg/kg
19 X 4 x 104 years 6 x 103
120 million years
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Residence Time for selected compo-nents of sea
water (note the extremely long residence times
for chloride and sodium)
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Conservative and Nonconservative Constituents
Conservative constituents of seawater are those
constituents that occur in constant proportions.
Conservative elements have long residence times
and are the most abundant dissolved material in
the ocean. Nonconservative constituents have
short residence times, and are usually associated
with seasonal, biological or short geological
cycles.
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Conservative and Nonconservative Constituents
Conservative constituents of seawater include
major salts such as sodium, chloride, and
sulfate. Nonconservative constituents include
nutrients such as phosphate and nitrate.
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Question

• If you poured a can of pop into the sea, how long
  would it take to for those molecules to mix?
• Throughout the surface water of the Pacific,
• ii) To a depth of 50m,
• iii) to a depth of 100m,
• iv) to a depth of 1000 m,
• v) to a depth of 3 km in the N. Atlantic,
• vi) to a Depth of 3 km in the N. Pacific.

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Mixing Times
Sea Surface
10 hours
1 year
50 m
2.5 years
2.5 years
1 km
Atlantic 100 years
Pacific 1000 years
4 km
N. Pole Equator S. Pole
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Conservative and Nonconservative Constituents
The mixing time of the ocean is 1600 years.
Conservative constituents are well mixed in the
ocean, therefore have residence times gt1600 years.
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Excess Constituents in Sea Water Volume cannot
be accounted for by river discharge What then is
the source of these excess consitutents,
including chloride, sulfate, and the water
itself? Degassing of the Earths interior
through volcanic eruptions is the answer. The
saltiness of sea water is the result of not
only river discharge, but also of volcanic
activity, especially on the ocean floor.
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Ocean ChemistryGases
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Gases Dissolve in Water
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Dissolved Gases
? Dissolved gases are required for life in the
ocean. ? Gas dissolves more readily in cold
water than it does on warm water ? Some
dissolved gases are conservative constituents in
seawater, others are nonconservative constituents.
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Dissolved Gases
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Dissolved N2

• ? Most abundant dissolved gas
• Not readily bioavailable
• N2 is conservative
• The Bends

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Dissolved O2

• ? 2nd most abundant dissolved gas
• Key for biology
• O2 is nonconservative
• Sources Photosynthesis Atmos
• Major sink Respiration

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Dissolved CO2

• ? 3nd most abundant dissolved gas
• Key for biology
• CO2 is nonconservative
• Sources Respiration Atmos
• Major sinks Photosynthesis mineral
  precipitation

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Dissolved CO2 O2
Important Reactions (transformations)
h?
Photosynthesis CO2 H2O ? CH2O O2
Respiration CH2O O2 ? CO2 H2O
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Dissolved CO2 O2Vertical profiles of these
gases in the ocean are strongly related to
photosynthesis in the surface zone, and
consumption of the primary plant producers by
zooplankton beneath the surface zone.
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• Nutrient Elements
• Phosphorus
• Nitrogen
• Silicon

Nutrient elements are non-conservative and vary
on the short term Essential for biologic
cycles Released by decay of organic matter on
sea floor Must be returned to surface by
upwelling, to be used in the photic zone by
phytoplankton (microscopic plants)