Dissolved Gases, CO2 and the Carbonate System

Question 1

What are the 5 units used when looking at dissolved gases in seawater?

Answer 1

vol/vol, mass/vol, uM, nM, % saturation

Question 2

Except for CO2, what happens to solubility with molecular mass and lower temperatures?

Answer 2

It increases

Question 3

Why is water super-saturated at the surface?

Answer 3

Because of wind, bubbles, spray and turbulence

Question 4

What are the three controls on oxygen distribution?

Answer 4

1. Its solubility at the relevant temperature and pressure
2. Biological processes which control production and consumption
3. Physical processes which control the rate of input and circulation (mixing)

Question 5

What is the general pattern of Oxygen in the oceans?

Answer 5

Maximum at the surface and a minimum at depth. It is the opposite pattern to the nutrients

Question 6

What is an Oxygen Minimum Zone (OMZ)?

Answer 6

An area with low dissolved oxygen at intermediate depths (50-1000m) because of reduced ventilation and high respiration rates

Question 7

Name 3 Oxygen Minimum Zones

Answer 7

Arabian Sea, Eastern Tropic North Pacific (ETNP) and Eastern Tropic South Pacific (ETSP)

Question 8

Why are the oceans no anoxic?

Answer 8

Because of the oceanic conveyor belt !

Question 9

How can you tell if a profile is simply due to mixing?

Answer 9

The T-S plot will be linear showing conservative behaviour

Question 10

3 Points about CO2 in the oceans

Answer 10

1. Solubility increases as temperature decreases (no molecular weight link)
2. CO2 reacts rather than dissolves
3. There are biological and chemical processes involved

Question 11

What is the bigger future threat regarding CO2 in the oceans?

Answer 11

Ocean Acidification

Question 12

What type of compound is CO2?

Answer 12

It is bio-intermediate - it increases by 20% with depth and is depleted at the surface by does not reach zero

Question 13

In which ocean is there more CO2 present?

Answer 13

The Pacific

Question 14

What does the dissolution of any material depend upon?

Answer 14

The degree of saturation of the solution (seawater)

Question 15

What is the formula for the saturation product?

Answer 15

Ksp = [Ca2+]saturated x [CO3 2-]saturated

Question 16

What are the ion activity product (IAP) and K used for?

Answer 16

To see if CaCO3 will dissolve you compare the actual water conditions to the saturation conditions using IAP and K

Question 17

What does D>1 mean?

Answer 17

Water is supersaturated

Question 18

What does D=1 mean?

Answer 18

Water is on saturation

Question 19

What does D<1 mean?

Answer 19

Water is undersaturated

Question 20

How do you calculate D?

Answer 20

[CO3 2-]observed / [CO3 2-]saturated

Question 21

Is Aragonite more or less soluble than Calcite?

Answer 21

More

Question 22

At depth what increases the solubility of aragonite and calcite?

Answer 22

Cold water and high pressure

Question 23

What is the distribution of seafloor sediments?

Answer 23

Carbonate isn’t present in the Pacific, there is not a uniform distribution and Siliceous sediments are rare as you need Si in surface waters

Question 24

What is the carbonate compensation depth?

Answer 24

The depth at which the rate of carbonate solution > or equal to the rate to supply

Question 25

What is the carbonate lysocline?

Answer 25

The depth at which there is a significant decrease in carbonate percentage

Question 26

What is the carbonate critical depth?

Answer 26

The depth below which there is <10% CaCO3

Question 27

Where is the carbonate critical depth shallower for Aragonite?

Answer 27

The Pacific

Question 28

Where is there a deeper saturation of Calcite and Aragonite?

Answer 28

The Atlantic