Seawater
Earth is an Ocean Planet
Topics
• Origin of the Ocean and
Atmosphere
• Hydrologic Cycle
• Biogeochemical Cycle
• Seawater Salinity
• Variations in Seawater
Chemistry
• Carbonic Acid System
Topics
• Origin of the Ocean and
Atmosphere
• Hydrologic Cycle
• Biogeochemical Cycle
• Seawater Salinity
• Variations in Seawater
Chemistry
• Carbonic Acid System
Seawater Salinity
Seawater Salinity
Major Constituents, Minor Constituents, Trace
Elements, and Gases
Seawater is 96.5% H2O (solvent)
Seawater is 96.5% H2O (solvent)
3.5% dissolved constituents (solutes)
Seawater Constituents
Seawater Constituents
• Four categories of solutes:
Seawater Constituents
• Four categories of solutes:
1. Major constituents
Seawater Constituents
• Four categories of solutes:
1. Major constituents
2. Minor constituents
Seawater Constituents
• Four categories of solutes:
1. Major constituents
2. Minor constituents
3. Trace elements
Seawater Constituents
• Four categories of solutes:
1. Major constituents
2. Minor constituents
3. Trace elements
4. Gases
Salinity
Salinity
• Salinity of seawater is relatively uniform
Salinity
• Salinity of seawater is relatively uniform
• Small changes are significant
Salinity
• Salinity of seawater is relatively uniform
• Small changes are significant
• Examples:
3.40%
3.49%
Average Salinity
Average Salinity
• 3.5%
Average Salinity
• 3.5%
• 3.5 per cent
Average Salinity
• 3.5%
• 3.5 per cent
• 3.5 parts per hundred
Average Salinity
• 3.5%
• 3.5 per cent
• 3.5 parts per hundred
• 35‰
Average Salinity
• 3.5%
• 35‰
• 3.5 per cent
• 35 per mil
• 3.5 parts per hundred
Average Salinity
• 3.5%
• 35‰
• 3.5 per cent
• 35 per mil
• 3.5 parts per hundred
• 35 parts per thousand
Average Salinity
• 3.5%
• 35‰
• 3.5 per cent
• 35 per mil
• 3.5 parts per hundred
• 35 parts per thousand
35 ppt
Average Salinity
• 3.5%
• 35‰
• 3.5 per cent
• 35 per mil
• 3.5 parts per hundred
• 35 parts per thousand
35 ppt
34.7 ppt
Major Constituents
Major Constituents
• Most seawater constituents are ions
Major Constituents
• Most seawater constituents are ions
• e.g. Cl- and Na+
Major Constituents
• Most seawater constituents are ions
• e.g. Cl- and Na+
• Six major constituents
Major Constituents
• Most seawater constituents are ions
• e.g. Cl- and Na+
• Six major constituents
• Constitute >99% of seawater salinity
Major Constituents
• Most seawater constituents are ions
• e.g. Cl- and Na+
• Six major constituents
• Constitute >99% of seawater salinity
• Concentrations of the major constituents
determine the salinity of seawater
Major Constituents
Major Constituents
1. Cl-
Major Constituents
1. Cl2. Na+
Major Constituents
1. Cl2. Na+
3. SO42-
Major Constituents
1. Cl2. Na+
3. SO424. Mg2+
Major Constituents
1. Cl2. Na+
3. SO424. Mg2+
5. Ca2+
Major Constituents
1. Cl2. Na+
3. SO424. Mg2+
5. Ca2+
6. K+
Major Constituents
1. Cl2. Na+
3. SO424. Mg2+
5. Ca2+
6. K+
Salinity of Seawater
Major Constituents
Major Constituents
NaCl
86%
Range of Salinity
Range of Salinity
• Salinity is relatively uniform - 35 ppt
Range of Salinity
• Salinity is relatively uniform - 35 ppt
• Salinity varies (over a small range)
Range of Salinity
• Salinity is relatively uniform - 35 ppt
• Salinity varies (over a small range)
• General range of variation in the open
ocean is 33-37 ppt
Range of Salinity
• Salinity is relatively uniform - 35 ppt
• Salinity varies (over a small range)
• General range of variation in the open
ocean is 33-37 ppt
33 ppt - 37 ppt
Marcet’s Principle
Marcet’s Principle
• Despite small variations in seawater
salinity, the relative proportions of the
major constituents are constant
Marcet’s Principle
• Despite small variations in seawater
salinity, the relative proportions of the
major constituents are constant
• Also called the principle of constant
proportions
Marcet’s Principle
Example of Marcet’s Principle:
Marcet’s Principle
Example of Marcet’s Principle:
• Station 1
Marcet’s Principle
Example of Marcet’s Principle:
• Station 1
• Salinity - 33.9 ppt
Marcet’s Principle
Example of Marcet’s Principle:
• Station 1
• Salinity - 33.9 ppt
• Cl/Na = x
Marcet’s Principle
Example of Marcet’s Principle:
• Station 1
• Salinity - 33.9 ppt
• Cl/Na = x
• Mg/K = y
Marcet’s Principle
Example of Marcet’s Principle:
• Station 1
• Salinity - 33.9 ppt
• Cl/Na = x
• Mg/K = y
• Ca/SO4 = z
Cl/Na
Cl/Na
Marcet’s Principle
• Station 1
• Salinity - 33.9 ppt
• Cl/Na = 1.8
• Mg/K = y
• Ca/SO4 = z
Mg/K
Mg/K
Marcet’s Principle
• Station 1
• Salinity - 33.9 ppt
• Cl/Na = 1.8
• Mg/K = 3.4
• Ca/SO4 = z
Ca/SO4
Ca/SO4
Marcet’s Principle
• Station 1
• Salinity - 33.9 ppt
• Cl/Na = 1.8
• Mg/K = 3.4
• Ca/SO4 = 0.15
Marcet’s Principle
• Station 1
• Salinity - 33.9 ppt
• Cl/Na = 1.8
• Mg/K = 3.4
• Ca/SO4 = 0.15
Marcet’s Principle
• Station 1
• Salinity - 33.9 ppt
• Cl/Na = 1.8
• Mg/K = 3.4
• Ca/SO4 = 0.15
• Station 2
Marcet’s Principle
• Station 1
• Station 2
• Salinity - 33.9 ppt
• Salinity - 36.3 ppt
• Cl/Na = 1.8
• Mg/K = 3.4
• Ca/SO4 = 0.15
Marcet’s Principle
• Station 1
• Station 2
• Salinity - 33.9 ppt
• Salinity - 36.3 ppt
• Cl/Na = 1.8
• Cl/Na = 1.8
• Mg/K = 3.4
• Ca/SO4 = 0.15
Marcet’s Principle
• Station 1
• Station 2
• Salinity - 33.9 ppt
• Salinity - 36.3 ppt
• Cl/Na = 1.8
• Cl/Na = 1.8
• Mg/K = 3.4
• Mg/K = 3.4
• Ca/SO4 = 0.15
Marcet’s Principle
• Station 1
• Station 2
• Salinity - 33.9 ppt
• Salinity - 36.3 ppt
• Cl/Na = 1.8
• Cl/Na = 1.8
• Mg/K = 3.4
• Mg/K = 3.4
• Ca/SO4 = 0.15
• Ca/SO4 = 0.15
Marcet’s Principle
Marcet’s Principle
• Despite small variations in seawater
salinity, the relative proportions of the
major constituents are constant
Marcet’s Principle
• Despite small variations in seawater
salinity, the relative proportions of the
major constituents are constant
• The principle of constant proportions
Determine Salinity
Determine Salinity
• Station 3: salinity = x
Determine Salinity
• Station 3: salinity = x
• To determine the salinity at a location,
oceanographers need to know the
concentrations of the major constituents
Determine Salinity
• Station 3: salinity = x
• To determine the salinity at a location,
oceanographers need to know the
concentrations of the major constituents
• Constitute >99% of seawater salinity
Determine Salinity
• Station 3: salinity = x
• To determine the salinity at a location,
oceanographers need to know the
concentrations of the major constituents
• Constitute >99% of seawater salinity
• Concentrations of the major constituents
determine the salinity of seawater
Major Constituents
Question
Question
• Considering Marcet’s principle -
Question
• Considering Marcet’s principle how many of the major constituents
must be measured to determine the
salinity of seawater?
Major Constituents
Determine Salinity
Determine Salinity
• Only need to measure the concentration
of one major constituent
Determine Salinity
• Only need to measure the concentration
of one major constituent
• Use Marcet’s principle to calculate the
concentrations of the other constituents
Determine Salinity
• Only need to measure the concentration
of one major constituent
• Use Marcet’s principle to calculate the
concentrations of the other constituents
• Which major constituent generally is
measured?
Determine Salinity
• Only need to measure the concentration
of one major constituent
• Use Marcet’s principle to calculate the
concentrations of the other constituents
• Which major constituent generally is
measured?
• Cl-
Determine Salinity
Determine Salinity
• Measure the concentration of Cl-
Determine Salinity
• Measure the concentration of Cl• Cl- = 19.35 ppt
Determine Salinity
• Measure the concentration of Cl• Cl- = 19.35 ppt
• Cl-/Na+ = 1.8
Determine Salinity
• Measure the concentration of Cl• Cl- = 19.35 ppt
• Cl-/Na+ = 1.8
• Na+/Cl- = 0.56
Determine Salinity
• Measure the concentration of Cl• Cl- = 19.35 ppt
• Cl-/Na+ = 1.8
• Na+/Cl- = 0.56
• 19.35 x 0.56 = 10.8 ppt
Determine Salinity
• Measure the concentration of Cl• Cl- = 19.35 ppt
measure Cl-
• Cl-/Na+ = 1.8
• Na+/Cl- = 0.56
• 19.35 x 0.56 = 10.8 ppt
calculate Na+
Determine Salinity
Determine Salinity
• Measure Cl-
Determine Salinity
• Measure Cl• Na+/Cl- = 0.56
Determine Salinity
• Measure Cl• Na+/Cl- = 0.56
• SO42-/Cl- = 0.14
Determine Salinity
• Measure Cl• Na+/Cl- = 0.56
• SO42-/Cl- = 0.14
• Mg2+/Cl- = 0.07
Determine Salinity
• Measure Cl• Na+/Cl- = 0.56
• SO42-/Cl- = 0.14
• Mg2+/Cl- = 0.07
• Ca2+/Cl- = 0.02
Determine Salinity
• Measure Cl• Na+/Cl- = 0.56
• SO42-/Cl- = 0.14
• Mg2+/Cl- = 0.07
• Ca2+/Cl- = 0.02
• K+/Cl- = 0.02
Determine Salinity
• Measure Cl• Na+/Cl- = 0.56
• SO42-/Cl- = 0.14
• Mg2+/Cl- = 0.07
• Ca2+/Cl- = 0.02
• K+/Cl- = 0.02
• 19.35 ppt
Determine Salinity
• Measure Cl-
• 19.35 ppt
• Na+/Cl- = 0.56
• 19.35 ppt x 0.56 = 10.8 ppt
• SO42-/Cl- = 0.14
• Mg2+/Cl- = 0.07
• Ca2+/Cl- = 0.02
• K+/Cl- = 0.02
Determine Salinity
• Measure Cl-
• 19.35 ppt
• Na+/Cl- = 0.56
• 19.35 ppt x 0.56 = 10.8 ppt
• SO42-/Cl- = 0.14
• 19.35 ppt x 0.14 = 2.7 ppt
• Mg2+/Cl- = 0.07
• Ca2+/Cl- = 0.02
• K+/Cl- = 0.02
Determine Salinity
• Measure Cl-
• 19.35 ppt
• Na+/Cl- = 0.56
• 19.35 ppt x 0.56 = 10.8 ppt
• SO42-/Cl- = 0.14
• 19.35 ppt x 0.14 = 2.7 ppt
• Mg2+/Cl- = 0.07
• 19.35 ppt x 0.07 = 1.3 ppt
• Ca2+/Cl- = 0.02
• K+/Cl- = 0.02
Determine Salinity
• Measure Cl-
• 19.35 ppt
• Na+/Cl- = 0.56
• 19.35 ppt x 0.56 = 10.8 ppt
• SO42-/Cl- = 0.14
• 19.35 ppt x 0.14 = 2.7 ppt
• Mg2+/Cl- = 0.07
• 19.35 ppt x 0.07 = 1.3 ppt
• Ca2+/Cl- = 0.02
• 19.35 ppt x 0.02 = 0.4 ppt
• K+/Cl- = 0.02
Determine Salinity
• Measure Cl-
• 19.35 ppt
• Na+/Cl- = 0.56
• 19.35 ppt x 0.56 = 10.8 ppt
• SO42-/Cl- = 0.14
• 19.35 ppt x 0.14 = 2.7 ppt
• Mg2+/Cl- = 0.07
• 19.35 ppt x 0.07 = 1.3 ppt
• Ca2+/Cl- = 0.02
• 19.35 ppt x 0.02 = 0.4 ppt
• K+/Cl- = 0.02
• 19.35 ppt x 0.02 = 0.4 ppt
Determine Salinity
• Measure Cl-
• 19.35 ppt
• Na+/Cl- = 0.56
• 19.35 ppt x 0.56 = 10.8 ppt
• SO42-/Cl- = 0.14
• 19.35 ppt x 0.14 = 2.7 ppt
• Mg2+/Cl- = 0.07
• 19.35 ppt x 0.07 = 1.3 ppt
• Ca2+/Cl- = 0.02
• 19.35 ppt x 0.02 = 0.4 ppt
• K+/Cl- = 0.02
• 19.35 ppt x 0.02 = 0.4 ppt
35.0 ppt
Determine Salinity
Determine Salinity
• To determine salinity within 1%, need to
know the concentrations of only the
major constituents
Determine Salinity
• To determine salinity within 1%, need to
know the concentrations of only the
major constituents
• Major constituents are >99% of salinity
Determine Salinity
• To determine salinity within 1%, need to
know the concentrations of only the
major constituents
• Major constituents are >99% of salinity
• Only have to measure one major
constituents to determine salinity
Determine Salinity
• To determine salinity within 1%, need to
know the concentrations of only the
major constituents
• Major constituents are >99% of salinity
• Only have to measure one major
constituents to determine salinity
• Measure one constituent and calculate
the others using Marcet’s principle
Determine Salinity
• To determine salinity within 1%, need to
know the concentrations of only the
major constituents
• Major constituents are >99% of salinity
• Only have to measure one major
constituents to determine salinity
• Measure one constituent and calculate
the others using Marcet’s principle
• Generally measure Cl-
Conservative Property
Conservative Property
• Concentrations of the major constituents are
conservative properties of seawater
Conservative Property
• Concentrations of the major constituents are
conservative properties of seawater
• Conservative properties are
Conservative Property
• Concentrations of the major constituents are
conservative properties of seawater
• Conservative properties are
1. altered primarily at the ocean’s surface
Conservative Property
• Concentrations of the major constituents are
conservative properties of seawater
• Conservative properties are
1. altered primarily at the ocean’s surface
2. not significantly affected by biological activity
Change Salinity
Change Salinity
• Salinity is altered primarily at the ocean’s
surface by
Change Salinity
• Salinity is altered primarily at the ocean’s
surface by
1. addition of water (precipitation)
Change Salinity
• Salinity is altered primarily at the ocean’s
surface by
1. addition of water (precipitation)
2. removal of water (evaporation)
Explains Marcet’s Principle
35 ppt
Na+
Cl-
Cl-
Cl-/Na+ = 1.8
Despite small variations in
seawater salinity, the relative
proportions of the major
constituents are constant
Explains Marcet’s Principle
35 ppt
Na+
Cl-
Na+
Cl-
Cl-/Na+ = 1.8
Cl-
Cl-
Explains Marcet’s Principle
35 ppt
Na+
Cl-
Cl-
Na+
Cl-
Cl-/Na+ = 1.8
Cl-
Explains Marcet’s Principle
35 ppt
37 ppt
Na+
Cl-
Cl-
Na+
Cl-
Cl-/Na+ = 1.8
Cl-
Explains Marcet’s Principle
35 ppt
37 ppt
Na+
Cl-
Cl-
Na+
Cl-
Cl-/Na+ = 1.8
Cl-
Cl-/Na+ = 1.8
Explains Marcet’s Principle
35 ppt
37 ppt
Na+
Cl-
Cl-
Na+
Cl-
Cl-/Na+ = 1.8
Na+
Cl-
Cl-/Na+ = 1.8
Cl-
Cl-
Explains Marcet’s Principle
35 ppt
37 ppt
Na+
Na+
Cl-
ClCl-
Na+
Cl-
Cl-/Na+ = 1.8
Cl-
Cl-/Na+ = 1.8
Cl-
Explains Marcet’s Principle
35 ppt
37 ppt
33 ppt
Na+
Na+
Cl-
ClCl-
Na+
Cl-
Cl-/Na+ = 1.8
Cl-
Cl-/Na+ = 1.8
Cl-
Explains Marcet’s Principle
35 ppt
37 ppt
33 ppt
Na+
Na+
Cl-
ClCl-
Na+
Cl-
Cl-/Na+ = 1.8
Cl-
Cl-
Cl-/Na+ = 1.8
Cl-/Na+ = 1.8
Uniformity of Salinity
Uniformity of Salinity
• Why is salinity relatively uniform?
Uniformity of Salinity
• Why is salinity relatively uniform?
a small open ocean range of 33-37 ppt
Uniformity of Salinity
• Why is salinity relatively uniform?
a small open ocean range of 33-37 ppt
• Uniform because the ocean is well mixed
Uniformity of Salinity
• Why is salinity relatively uniform?
a small open ocean range of 33-37 ppt
• Uniform because the ocean is well mixed
• To explain how the ocean became well mixed,
oceanographers use the
Uniformity of Salinity
• Why is salinity relatively uniform?
a small open ocean range of 33-37 ppt
• Uniform because the ocean is well mixed
• To explain how the ocean became well mixed,
oceanographers use the
long residence times of the major constituents
Uniformity of Salinity
• Why is salinity relatively uniform?
a small open ocean range of 33-37 ppt
• Uniform because the ocean is well mixed
• To explain how the ocean became well mixed,
oceanographers use the
long residence times of the major constituents
short mixing time of the ocean
All of the major constituents
have residence times > 106 yr
Ocean Mixing pattern
Atlantic
Indian
Pacific
Ocean Mixing pattern
Atlantic
Indian
Pacific
Ocean Mixing pattern
Atlantic
Indian
Pacific
Ocean Mixing pattern
Atlantic
Indian
Pacific
Ocean Mixing pattern
Atlantic
Indian
Pacific
Ocean Mixing pattern
Atlantic
Indian
Pacific
Mixing time ≈ 1000 yr
Ocean Mixing pattern
Mixing time ≈ 1000 yr
Ocean Is Well Mixed
Ocean Is Well Mixed
• Residence times of the major constituents are
much, much longer than the mixing time
Ocean Is Well Mixed
• Residence times of the major constituents are
much, much longer than the mixing time
1,000,000 yr >>> 1,000 yr
Ocean Is Well Mixed
• Residence times of the major constituents are
much, much longer than the mixing time
1,000,000 yr >>> 1,000 yr
106 yr >>> 103 yr
Ocean Is Well Mixed
• Residence times of the major constituents are
much, much longer than the mixing time
1,000,000 yr >>> 1,000 yr
106 yr >>> 103 yr
• Residence time/mixing time = X
Ocean Is Well Mixed
• Residence times of the major constituents are
much, much longer than the mixing time
1,000,000 yr >>> 1,000 yr
106 yr >>> 103 yr
• Residence time/mixing time = X
106 yr/103 yr = 103
Ocean Is Well Mixed
• Residence times of the major constituents are
much, much longer than the mixing time
1,000,000 yr >>> 1,000 yr
106 yr >>> 103 yr
• Residence time/mixing time = X
106 yr/103 yr = 103
• In 1,000,000 yr, the ocean mixes itself 1000x
Minor Constituents
and Trace Elements
Minor Constituents
and Trace Elements
• Minor constituents measured in ppm
Minor Constituents
and Trace Elements
• Minor constituents measured in ppm
• Trace elements measured in ppb or pptr
Minor Constituents
and Trace Elements
• Minor constituents measured in ppm
• Trace elements measured in ppb or pptr
• In general,
Minor Constituents
and Trace Elements
• Minor constituents measured in ppm
• Trace elements measured in ppb or pptr
• In general,
Marcet’s principle does not apply
Minor Constituents
and Trace Elements
• Minor constituents measured in ppm
• Trace elements measured in ppb or pptr
• In general,
Marcet’s principle does not apply
tend to be nonconservative
Minor Constituents
and Trace Elements
• Minor constituents measured in ppm
• Trace elements measured in ppb or pptr
• In general,
Marcet’s principle does not apply
tend to be nonconservative
tend to have shorter residence times
Biolimiting Nutrients
Biolimiting Nutrients
• Primary biolimiting nutrients are in trace
concentrations:
N, P, Si, Fe
Nutrient concentrations are low in the open ocean
Nutrient concentrations are low in the open ocean
Water is clear
Atmospheric Gases
Gases
Gases
• Atmospheric Gases
Gases
• Atmospheric Gases
N2 - 78%
Gases
• Atmospheric Gases
N2 - 78%
O2 - 21%
Gases
• Atmospheric Gases
N2 - 78%
O2 - 21%
CO2 - 0.035%
Gases
• Atmospheric Gases
N2 - 78%
O2 - 21%
CO2 - 0.035%
• Oceanic Gases
Gases
• Atmospheric Gases
N2 - 78%
O2 - 21%
CO2 - 0.035%
• Oceanic Gases
N2 - 48%
Gases
• Atmospheric Gases
• Oceanic Gases
N2 - 78%
N2 - 48%
O2 - 21%
O2 - 36%
CO2 - 0.035%
Gases
• Atmospheric Gases
• Oceanic Gases
N2 - 78%
N2 - 48%
O2 - 21%
O2 - 36%
CO2 - 0.035%
CO2 - 15%
Gases
Gases
• Are N2, O2, and CO2 conservative or
nonconservative?
Gases
• Are N2, O2, and CO2 conservative or
nonconservative?
• N2 is conservative
Gases
• Are N2, O2, and CO2 conservative or
nonconservative?
• N2 is conservative
• O2 is nonconservative
Gases
• Are N2, O2, and CO2 conservative or
nonconservative?
• N2 is conservative
• O2 is nonconservative
• CO2 is nonconservative
Gases
• Are N2, O2, and CO2 conservative or
nonconservative?
• N2 is conservative
• O2 is nonconservative
• CO2 is nonconservative
Both O2 and CO2 are strongly affected
by biological activity
Gases
• Are N2, O2, and CO2 conservative or
nonconservative?
• N2 is conservative
• O2 is nonconservative
• CO2 is nonconservative
Both O2 and CO2 are strongly affected
by biological activity
The concentrations of O2 and CO2 are
altered below the ocean’s surface
Banded Ironstone
Variations in
Seawater Chemistry
Next
Variations in
Seawater Chemistry