Sea salt: Composition, source and fate

Question 1

99% of all the salt ions in the sea are:

Answer 1

• Sodium (Na+)
• Chloride (Cl-)
• Sulfate (SO4-2)
• Magnesium (Mg+2)
• Calcium (Ca+2)
• Potassium (K+)

Question 2

Conservative properties of sea water

Answer 2

• Nitrogen and the noble gases (inert because they are chemically non-reactive)

Question 2

86% of the salt in the sea

Answer 2

Sodium and chloride

Question 3

Major nutrients in the sea are compounds of :

Answer 3

• Phosphorus - 0.07ppm
• Nitrogen - 0.5 ppm
• Silicon- 3ppm

Question 4

Non- conservative property of the sea

Answer 4

= Concentration of nutrients - vary greatly over time
= Oxygen and CO2 due to biological recycling

Question 5

In order of decreasing abundance the major gases in the sea are:

Answer 5

1. Nitrogen (N2)
2. Oxygen (O2)
3. Carbon Dioxide (CO2)
4. The noble gases (Ar,Ne,He)

Question 6

Trace elements

Answer 6

Occurs in minute quantities (ppm or ppb).
n small quantities can be important for either promoting or killing life

Question 7

Nitrogenase

Answer 7

Enzyme that is used to fix nitrogen- the reduction of nitrogen to ammonia uses iron in its active site

Question 8

Marine organic compounds

Answer 8

Occur in low concentrations and consist of large complex molecules such as :
- fat
- Proteins
- Carbohydrates
- Hormones
- Vitamins

Question 9

Organic compounds

Answer 9

Molecules are produced by organisms (faeces) or through decay

Question 10

Why is the sea salty?

Answer 10

• On land, PRECIPITATION exceeds evaporation- run off carries dissolved salts from land
• In the Ocean, EVAPORATION exceeds precipitation- evaporating water leaves salts behind

Question 11

Salt in seawater

Answer 11

35 g/kg (35%)

Question 12

Not all products of chemical weathering is carried into the sea

Answer 12

Most Si, Al and Fe is left behind on land

Question 13

Dissolution of CO2 in water

Answer 13

CO2+H2O<–> H2CO3
H2CO3<–> HCO3-+ H+
HCO3-<–> CO32-+ H+

Question 14

Dissolved substances in river water

Answer 14

Not the same proportions as those in oceans

Question 15

Why does sodium have a higher concentration in seawater than minerals such as Ca, Mg and K?

Answer 15

Na is more soluble than other elements.

Question 16

Processes regulating seawater salts

Answer 16

• Primordial source from Earth’s interior
• Volcanic gases that fall as rain
• Fluids introduced at ridge crests/vents
• River outflow into the ocean
• Dusts from land (aeolian transport)

Question 17

Salt sinks examples

Answer 17

• Wind blows sea spray
• Absorption of clays into organic matter
• Shells and organic matter formation by organisms
• Volcanic reactions under the sea
• Burial in sediments

Question 18

Balance of inputs and outputs

Answer 18

• Seawater composition uniforms through time over the last 1.5 Ga

Question 19

Residence Time

Answer 19

• Ions with long residence time tend to accumulate in the sea
• Ions with short residence time are removed
• Rapid mixing and long residence times explain the constant composition of sea water

Question 20

Mixing time

Answer 20

The time it takes for any variation to be homogenised. it is the property of the forces acting on the fluid and the size of the reservoir.

Question 21

Steady state (no change in reservoir content)

Answer 21

Flux in = flux out

Question 22

The principle of constant proportion

Answer 22

The absolute amount of salt in seawater varies, but the relative proportions of the ions is constant