Dissolved Gases, CO2 and the Carbonate System Flashcards
What are the 5 units used when looking at dissolved gases in seawater?
vol/vol, mass/vol, uM, nM, % saturation
Except for CO2, what happens to solubility with molecular mass and lower temperatures?
It increases
Why is water super-saturated at the surface?
Because of wind, bubbles, spray and turbulence
What are the three controls on oxygen distribution?
- Its solubility at the relevant temperature and pressure
- Biological processes which control production and consumption
- Physical processes which control the rate of input and circulation (mixing)
What is the general pattern of Oxygen in the oceans?
Maximum at the surface and a minimum at depth. It is the opposite pattern to the nutrients
What is an Oxygen Minimum Zone (OMZ)?
An area with low dissolved oxygen at intermediate depths (50-1000m) because of reduced ventilation and high respiration rates
Name 3 Oxygen Minimum Zones
Arabian Sea, Eastern Tropic North Pacific (ETNP) and Eastern Tropic South Pacific (ETSP)
Why are the oceans no anoxic?
Because of the oceanic conveyor belt !
How can you tell if a profile is simply due to mixing?
The T-S plot will be linear showing conservative behaviour
3 Points about CO2 in the oceans
- Solubility increases as temperature decreases (no molecular weight link)
- CO2 reacts rather than dissolves
- There are biological and chemical processes involved
What is the bigger future threat regarding CO2 in the oceans?
Ocean Acidification
What type of compound is CO2?
It is bio-intermediate - it increases by 20% with depth and is depleted at the surface by does not reach zero
In which ocean is there more CO2 present?
The Pacific
What does the dissolution of any material depend upon?
The degree of saturation of the solution (seawater)
What is the formula for the saturation product?
Ksp = [Ca2+]saturated x [CO3 2-]saturated
What are the ion activity product (IAP) and K used for?
To see if CaCO3 will dissolve you compare the actual water conditions to the saturation conditions using IAP and K
What does D>1 mean?
Water is supersaturated
What does D=1 mean?
Water is on saturation
What does D<1 mean?
Water is undersaturated
How do you calculate D?
[CO3 2-]observed / [CO3 2-]saturated
Is Aragonite more or less soluble than Calcite?
More
At depth what increases the solubility of aragonite and calcite?
Cold water and high pressure
What is the distribution of seafloor sediments?
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
What is the carbonate compensation depth?
The depth at which the rate of carbonate solution > or equal to the rate to supply
What is the carbonate lysocline?
The depth at which there is a significant decrease in carbonate percentage
What is the carbonate critical depth?
The depth below which there is <10% CaCO3
Where is the carbonate critical depth shallower for Aragonite?
The Pacific
Where is there a deeper saturation of Calcite and Aragonite?
The Atlantic
