Composition of Ocean Waters

Salts and Salinity

Ions

Ions are stable forms of elements that acquirean electrical charge by gaining or losing electrons

Elements that lose electrons and becomepositively charged are called cations.

Elements that gain electrons and becomenegatively charged are called anions.

Cations: K+, Na+, Mg2+, Ca2+

Anions: Cl-, CO3-2, SO4

-2

Salts

KCl, NaCl, MgCl2, CaCO3, CaSO4

Cations: K+, Na+, Mg2+, Ca2+

Anions: Cl-, CO3-2, SO4

-2

Salts are formed by combining cations andanions to form solids that have no charge.

K+ + Cl- = KCl

Ca+2 + 2Cl- = CaCl2

Conversely, if solid salts are mixed with water they dissolve and the ions go into solution

KCl K+ + Cl-

NaCl Na+ + Cl-Water

Water

solid solution

CaCO3

CaSO4

Ca+2 and CO3-2

Ca+2 and SO4-2

Ocean Salinity originates from dissolutionof salts and erosion of rocks and minerals

as water moves at or below the earth surface

River water contains dilute amounts of dissolved salts that are ultimately delivered to the oceans

As water evaporates, the oceans concentrate the salts to levels farexceeding those found in rivers.

Average Ocean Salinity = 3.5%

What kind of Salts?

KCl

NaCl

MgCl2

CaCO3

CaSO4

KCl

NaCl

MgCl2

CaCO3

CaSO4

River Water35.1520.3912.14 11.675.685.793.412.12

IonCarbonateCalciumSulfate SilicateChlorideSodium

MagnesiumPotassium

River Salt Composition

Dominated by Carbonate, Calcium, Sulfate, and Silicate

KAlSi3O8

CaAl2Si2O8

NaAlSi3O8

KAlSi3O8

CaAl2Si2O8

NaAlSi3O8

Ocean Salt Composition

IonChlorideSodiumSulfate

Magnesium Calcium

Potassium Carbonate

Silicate

Sea Water (%)55.0430.627.683.69 1.151.100.40

.0004

Dominated by Chloride and Sodium

Na+ and Cl-(85% of total)

Cl- Na+

River Water35.1520.3911.6712.14 5.685.793.412.12

Sea Water.40

1.15.00047.68

55.0430.623.691.10

IonCarbonateCalciumSilicateSulfate ChlorideSodium

MagnesiumPotassium

Percentage of Total Dissolved Minerals

} 79%

} 85%

• Enrich Chloride and Sodium in ocean water

Remove Silica, Calcium, Carbonate from river water

Alterations

sodium, potassium, and ammonium salts are soluble

chloride, bromide and iodide salts are soluble.

NaCl Solubility 350 g/L

Solubility: ease of salt dissolution in water

Enriching Sodium and Chloride

Once these types of ions reach the oceans they stay dissolved

IonChlorideSodiumSulfate

Magnesium Calcium

Potassium Carbonate

Silicate

Sea Water (%)55.0430.627.683.69 1.151.100.40

.0004

Both chloride salts and sodium salts areextremely soluble in water and do not

combine with other elements to form solids

• Enrich Chloride and Sodium in ocean water

Remove Silica, Calcium, Carbonate from river water

Alterations

Calcium and Carbonate Removal

Incorporation into shells of marine invertebrates

Ca2+ + CO32- = CaCO3

Diatoms

Life and Silica

• Remove Silica, Calcium, Carbonate

Use silica as structural material

River Water35.1520.3911.675.685.793.412.12

12.14

Sea Water.40

1.15.000455.0430.623.691.107.68

IonCarbonateCalciumSilicateChlorideSodium

MagnesiumPotassium

Sulfate

Percentage of Total Dissolved Minerals

Extra Credit Questions

1. Cations become positively/negatively charged by gaining/losing electrons.

2. The dominant ion in river water is ___

3. The dominant ion in sea water is ___

4. Marine invertebrate shells are made from ____

Other Constituents in Ocean Water

The Oceans, Heat, and Carbon Dioxide

Middle Ages

IndustrialRevolution

380 ppm

CO2

Global Temperature

Ocean Temperature

Oceans can buffer changesin atmospheric temperature

GasGases/Heat

Present and Future Problems

Warmer oceans ?

October, 2005

Rising CO2 and Ocean Chemistry

Gases Dissolve in Water

GasGases

dissolution

Composition of the Atmosphere

Gases

Nitrogen 78.1%Oxygen 20.9%Argon 0.93%CO2 0.038%

Oxygen

Solubility: 0.043 g/L(20oC)

Carbon Dioxide

C

O

O-

-

+

Solubility = 1.69 g/L

Middle Ages

IndustrialRevolution

removed about 118 billion metric tons of CO2.

Between 1800 and 1994, the oceans have

Equivalent to 48 percent of all fossil fuel emissions

380 ppm

Solubility = 1.69 g/L

CO2

Buffering

Carbon Dioxide also is an Acid

CO2

WaterAcid

CO2 + H2O H2CO3

H2CO3 H+ + HCO3-

H+ is acid

Acids (H+) are reactive and dissolve a number of substances

Dissolution of Carbon Dioxide

Common Acid Dissolution

CuO + 2HCl → CuCl2 + H2O

Ag2O + 2 HCl → 2 AgCl + H2O

CaCO3 + H+ Ca2+ + HCO3-

Fe2O3 + 6H+ 2Fe3+ + 3H2OFe2O3

CaCO3

Invertebrate shells and skeletons largely CaCO3

Corals, “lithic” plankton, clams, oysters

CaCO3 + H+ Ca2+ + HCO3-

CO2

WaterH+

Acidification of the oceans Inhibits the calcification and

growth of invertebrates

Analysis of coral cores shows a steady drop in calcification over the last 20 years

pH change: 8.179 to 8.104

Coral Reef Bleaching

http://www.npr.org/templates/story/story.php?storyId=17243164

Temperature and Acidity

Anthropogenic Inputs of Solutes to the Oceans

Homework II Oceanic Dead Zones

Due Friday, October 2nd in class

Assignment is posted on the website