Seawater constituent

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 SalinityMajor Constituents, Minor Constituents, Trace

Elements, and Gases

Seawater is 96.5% H2O (solvent)

3.5% dissolved constituents (solutes)

Seawater Constituents

• Four categories of solutes:

• Four categories of solutes:1. Major constituents

• Four categories of solutes:1. Major constituents2. Minor constituents

• Four categories of solutes:1. Major constituents2. Minor constituents3. Trace elements

• Four categories of solutes:1. Major constituents2. Minor constituents3. Trace elements4. Gases

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

• 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

• 35‰

Average Salinity

• 3.5%

• 3.5 per cent

• 35‰

• 35 per mil

Average Salinity

• 3.5%

• 3.5 per cent

• 35‰

• 35 per mil

• 35 parts per thousand

Average Salinity

• 3.5%

• 3.5 per cent

• 35‰

• 35 per mil

35 ppt

Average Salinity

• 3.5%

• 3.5 per cent

• 35‰

• 35 per mil

35 ppt34.7 ppt

Major Constituents

• Most seawater constituents are ions

Major Constituents

• Most seawater constituents are ions• e.g. Cl- and Na+

Major Constituents

• Six major constituents

Major Constituents

• Six major constituents• Constitute >99% of seawater salinity

Major Constituents

• Six major constituents• Constitute >99% of seawater salinity• Concentrations of the major constituents

determine the salinity of seawater

Major Constituents

1. Cl-

Major Constituents

1. Cl-

2. Na+

Major Constituents

1. Cl-

2. Na+

3. SO42-

Major Constituents

1. Cl-

2. Na+

3. SO42-

4. Mg2+

Major Constituents

1. Cl-

2. Na+

3. SO42-

4. Mg2+

5. Ca2+

Major Constituents

1. Cl-

2. Na+

3. SO42-

4. Mg2+

5. Ca2+

Major Constituents

1. Cl-

2. Na+

3. SO42-

4. Mg2+

5. Ca2+

Salinity of Seawater

Major Constituents

NaCl86%

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

• Despite small variations in seawater salinity, the relative proportions of the major constituents are constant

• Also called the principle of constant proportions

Example of Marcet’s Principle:

• Station 1

• Station 1• Salinity - 33.9 ppt

• Station 1• Salinity - 33.9 ppt• Cl/Na = x

• Station 1• Salinity - 33.9 ppt• Cl/Na = x• Mg/K = y

• Station 1• Salinity - 33.9 ppt• Cl/Na = x• Mg/K = y• Ca/SO4 = z

• Station 1• Salinity - 33.9 ppt• Cl/Na = 1.8• Mg/K = y• Ca/SO4 = z

• Station 1• Salinity - 33.9 ppt• Cl/Na = 1.8• Mg/K = 3.4• Ca/SO4 = z

Ca/SO4

• Station 1• Salinity - 33.9 ppt• Cl/Na = 1.8• Mg/K = 3.4• Ca/SO4 = 0.15

• Station 2

• Station 2• Salinity - 36.3 ppt

• Station 2• Salinity - 36.3 ppt• Cl/Na = 1.8

• Station 2• Salinity - 36.3 ppt• Cl/Na = 1.8• Mg/K = 3.4

• The principle of constant proportions

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

• Constitute >99% of seawater salinity

Determine Salinity

• Constitute >99% of seawater salinity• Concentrations of the major constituents

determine the salinity of seawater

Major Constituents

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

• Only need to measure the concentration of one major constituent

Determine Salinity

• Use Marcet’s principle to calculate the concentrations of the other constituents

Determine Salinity

• Which major constituent generally is measured?

Determine Salinity

• Which major constituent generally is measured?

• Cl-

Determine Salinity

• Measure the concentration of Cl-

Determine Salinity

• Cl- = 19.35 ppt

Determine Salinity

• Cl- = 19.35 ppt• Cl-/Na+ = 1.8

Determine Salinity

• Cl- = 19.35 ppt• Cl-/Na+ = 1.8• Na+/Cl- = 0.56

Determine Salinity

• Cl- = 19.35 ppt• Cl-/Na+ = 1.8• Na+/Cl- = 0.56• 19.35 x 0.56 = 10.8 ppt

Determine Salinity

• Cl- = 19.35 ppt• Cl-/Na+ = 1.8• Na+/Cl- = 0.56• 19.35 x 0.56 = 10.8 ppt

measure Cl-

calculate Na+

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-

• Na+/Cl- = 0.56

• SO42-/Cl- = 0.14

• Mg2+/Cl- = 0.07

• Ca2+/Cl- = 0.02

• K+/Cl- = 0.02

• 19.35 ppt

• 19.35 ppt x 0.56 = 10.8 ppt

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

• 19.35 ppt x 0.56 = 10.8 ppt

• 19.35 ppt x 0.14 = 2.7 ppt

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

• 19.35 ppt x 0.56 = 10.8 ppt

• 19.35 ppt x 0.14 = 2.7 ppt

• 19.35 ppt x 0.07 = 1.3 ppt

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

• 19.35 ppt x 0.56 = 10.8 ppt

• 19.35 ppt x 0.14 = 2.7 ppt

• 19.35 ppt x 0.07 = 1.3 ppt

• 19.35 ppt x 0.02 = 0.4 ppt

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

• 19.35 ppt x 0.56 = 10.8 ppt

• 19.35 ppt x 0.14 = 2.7 ppt

• 19.35 ppt x 0.07 = 1.3 ppt

• 19.35 ppt x 0.02 = 0.4 ppt

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

• 19.35 ppt x 0.56 = 10.8 ppt

• 19.35 ppt x 0.14 = 2.7 ppt

• 19.35 ppt x 0.07 = 1.3 ppt

• 19.35 ppt x 0.02 = 0.4 ppt

35.0 ppt

Determine Salinity

• To determine salinity within 1%, need to know the concentrations of only the major constituents

Determine Salinity

• Major constituents are >99% of salinity

Determine Salinity

• Major constituents are >99% of salinity• Only have to measure one major

constituents to determine salinity

Determine Salinity

constituents to determine salinity• Measure one constituent and calculate

the others using Marcet’s principle

Determine Salinity

constituents to determine salinity• Measure one constituent and calculate

the others using Marcet’s principle• Generally measure Cl-

Conservative Property

• Concentrations of the major constituents are conservative properties of seawater

• Conservative properties are

• Conservative properties are1. altered primarily at the ocean’s surface

• Conservative properties are1. altered primarily at the ocean’s surface2. not significantly affected by biological activity

Change Salinity

• Salinity is altered primarily at the ocean’s surface by

Change Salinity

1. addition of water (precipitation)

Change Salinity

1. addition of water (precipitation)2. removal of water (evaporation)

Change Salinity

Explains Marcet’s Principle

Cl- Cl-

35 ppt

Cl-/Na+ = 1.8

Despite small variations in seawater salinity, the relative

proportions of the major constituents are constant

Cl- Cl-

35 ppt

Cl-/Na+ = 1.8

Cl- Cl-

35 ppt

Cl-/Na+ = 1.8

Cl- Cl-

35 ppt

Cl-/Na+ = 1.8

Cl- Cl-

37 ppt

Cl- Cl-

35 ppt

Cl-/Na+ = 1.8

Cl- Cl-

37 ppt

Cl-/Na+ = 1.8

Cl- Cl-

35 ppt

Cl-/Na+ = 1.8

Cl- Cl-

37 ppt

Cl-/Na+ = 1.8

Cl- Cl-

35 ppt

Cl-/Na+ = 1.8

Cl- Cl-

37 ppt

Cl-/Na+ = 1.8

Cl- Cl-

35 ppt

Cl-/Na+ = 1.8

Cl- Cl-

37 ppt

Cl-/Na+ = 1.8

33 ppt

Cl- Cl-

35 ppt

Cl-/Na+ = 1.8

Cl- Cl-

37 ppt

Cl-/Na+ = 1.8

33 ppt

Cl-/Na+ = 1.8

Uniformity of Salinity

• Why is salinity relatively uniform?

• Why is salinity relatively uniform?a small open ocean range of 33-37 ppt

• Uniform because the ocean is well mixed

• Uniform because the ocean is well mixed• To explain how the ocean became well mixed,

oceanographers use the

oceanographers use thelong residence times of the major constituents

oceanographers use thelong residence times of the major constituentsshort mixing time of the ocean

All of the major constituentshave residence times > 106 yr

Ocean Mixing pattern

Atlantic Indian Pacific

Mixing time ≈ 1000 yr

Ocean Is Well Mixed

• Residence times of the major constituents are much, much longer than the mixing time

Ocean Is Well Mixed

1,000,000 yr >>> 1,000 yr

Ocean Is Well Mixed

1,000,000 yr >>> 1,000 yr106 yr >>> 103 yr

Ocean Is Well Mixed

1,000,000 yr >>> 1,000 yr106 yr >>> 103 yr

• Residence time/mixing time = X

Ocean Is Well Mixed

1,000,000 yr >>> 1,000 yr106 yr >>> 103 yr

• Residence time/mixing time = X106 yr/103 yr = 103

Ocean Is Well Mixed

1,000,000 yr >>> 1,000 yr106 yr >>> 103 yr

• Residence time/mixing time = X106 yr/103 yr = 103

• In 1,000,000 yr, the ocean mixes itself 1000x

Minor Constituentsand Trace Elements

• Minor constituents measured in ppm

• Minor constituents measured in ppm• Trace elements measured in ppb or pptr

• Minor constituents measured in ppm• Trace elements measured in ppb or pptr• In general,

Marcet’s principle does not apply

Marcet’s principle does not applytend to be nonconservative

Marcet’s principle does not applytend to be nonconservativetend to have shorter residence times

Biolimiting Nutrients

• Primary biolimiting nutrients are in trace concentrations:

N, P, Si, Fe

Nutrient concentrations are low in the open ocean

Water is clear

Atmospheric Gases

• Atmospheric Gases

N2 - 78%

O2 - 21%

N2 - 78%

O2 - 21%

CO2 - 0.035%

N2 - 78%

O2 - 21%

CO2 - 0.035%

• Oceanic Gases

N2 - 78%

O2 - 21%

CO2 - 0.035%

• Oceanic Gases

N2 - 48%

N2 - 78%

O2 - 21%

CO2 - 0.035%

• Oceanic Gases

N2 - 48%

O2 - 36%

N2 - 78%

O2 - 21%

CO2 - 0.035%

• Oceanic Gases

N2 - 48%

O2 - 36%

CO2 - 15%

• Are N2, O2, and CO2 conservative or nonconservative?

• N2 is conservative

• N2 is conservative• O2 is nonconservative

• N2 is conservative• O2 is nonconservative• CO2 is nonconservative

Both O2 and CO2 are strongly affected by biological activity

Both O2 and CO2 are strongly affected by biological activityThe concentrations of O2 and CO2 are altered below the ocean’s surface

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Seawater constituent

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