Dissolved Gases in the oceans - O2, CO2 and the Carbonate system

Question 1

What controls the solubility of gases in water?

Answer 1

Distribution of oxygen - profiles and around the ocean system

Question 2

How can we show non-conservative behavior?

Answer 2

The CO2 system and equilibrium

Question 3

How can dissolved gases in sea water be expressed?

Answer 3

Vol/vol; mass/vol; chemical units such as micromoles (uM); or %saturation

Question 4

How to calculate %saturation of dissolved gases in seawater?

Answer 4

Knowing the solubility of gas in water and partial pressure in dry air we can calculate the equilibrium concentration at a given pressure and temperature

Question 5

How can O2 solubility be above 100%?

Answer 5

Due to turbulence

Question 6

What is O2 distribution controlled by?

Answer 6

1) Solubility at relavant Temperature and pressure. 2) Biological processes which control production and consumption. 3) Physical processes that control the rate of input and circulation - mixing

Question 7

What is the general pattern of O2 in seawater?

Answer 7

Max at sfc from mixing and liberated by photosynthesis - O2 minimum at depth, intensity depends on amount of organic matter being respired (opposite to N and P).
Variation in deep water dependent on ocean circulation and water masses

Question 8

What is the result of an intense O2 minimum?

Answer 8

Can lead to anoxic waters

Question 9

Whats an OMZ?

Answer 9

Oxygen minimum zone

Question 10

Where are OMZ’s?

Answer 10

At intermediate depths (50-1000m)

Question 11

What caused intermediate depth OMZ’s?

Answer 11

Reduced ventilation and high respiration rates of settling organic matter produced at surface waters.

Question 12

What is OMZ’s important for?

Answer 12

Although a small% of global ocean they are a significant sink for nitrogen 30-50% N removal in the oceans.

Question 13

How is Nitrogen removed in the OMZ nitrogen sink?

Answer 13

Denitrification (Dissolved nitrogen being reduced to nitrogen gas by bacteria).

Question 14

What are OMZ’s an important source of and how?

Answer 14

Greenhouse gases as a by product of respiration (CO2) and denitrification (N20).

Question 15

Why are the oceans not anoxic?

Answer 15

Global circulation currents - cold dense water sinking (O2 more soluble in cold water) this REVENTILATES the bottom of the oceans PROVIDED that there is no barrier to circulation (Fjiords, semi-enclosed seas)

Question 16

How to tell is an O2 profile is simply to do with mixing

Answer 16

Linear profile = Due to mixing. Non-linear profile relative to mixing line = a parameter being added or removed by a chemical or biological process, (non conservative behavior)

Question 17

Why are concentrations of O2 in Atlantic deep waters generally greater than in the Pacific?

Answer 17

Because Atlantic deep waters have more recently left the sea surface so have had less time to lose O2 to oxidation of organic matter.

Question 18

What is different about CO2 in terms of solubility in water?

Answer 18

It is very soluble in cold and warm water

Question 19

Describe the potential long term problem if CO2 increases?

Answer 19

Atmospheric CO2 dissolves into ocean and mixes with water to form Carbonic acid, (H2CO3) these get converted through chemical and biologicl prcoesses into Bicarbonate ions and Hydrogen ions and Carbonate ions. This process INCREASES OCEAN ACIDITY.

Question 20

What is the general alkalinity trend for the Atlantic and pacific oceans?

Answer 20

Pacific = Lower surface water; increase intermediate water; slight decrease deep water. Atlantic = Higher surface water, sharp decrease through first 1000m, slight increase through intermediate and deep water

Question 21

What does dissolution of any material depend on?

Answer 21

The degree of saturation of the solution (seawater)

Question 22

What are carbonate ion concentrations in seawater mostly determined by, Temp’ or Pressure

Answer 22

Pressure determines higher saturation values of calcite and aragonite over temperature. Therefore abundance a function of depth

Question 23

Calcite and Aragonite (Carbonates) are more soluble under what conditions?

Answer 23

Low temperature, high pressure - At Depth!

Question 24

What is the difference between CaCO3 and SiO2 deep sea sediment distribution?

Answer 24

CaCo3 more widely distributed than SiO2 as it justneed Ca and CO3^2- to form whereas siliceous sediments also need Si in the surface which is rare as it it biolimited

Question 25

What is the Carbonate Lysocline?

Answer 25

Depth at which large decrease in carbonate %

Question 26

What is carbonate compensation depth?

Answer 26

Depth at which rate of carbonate solution = or exceeds rate of supply

Question 27

What is carbonate critical depth

Answer 27

Depth below which there is < 10% CaCO3

Question 28

What is the long terms effects of increase CO2 in oceans

Answer 28

Decrease in alkalinity - chemical processes lead to under saturation of carbonates such as aragonite in the southern ocean. Hence calcifying organisms will be increasingly limited in their ability to deposit hard parts which is a serious perturbation to the biological carbon pump