Dissolved Gases in the oceans - O2, CO2 and the Carbonate system Flashcards
What controls the solubility of gases in water?
Distribution of oxygen - profiles and around the ocean system
How can we show non-conservative behavior?
The CO2 system and equilibrium
How can dissolved gases in sea water be expressed?
Vol/vol; mass/vol; chemical units such as micromoles (uM); or %saturation
How to calculate %saturation of dissolved gases in seawater?
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
How can O2 solubility be above 100%?
Due to turbulence
What is O2 distribution controlled by?
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
What is the general pattern of O2 in seawater?
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
What is the result of an intense O2 minimum?
Can lead to anoxic waters
Whats an OMZ?
Oxygen minimum zone
Where are OMZ’s?
At intermediate depths (50-1000m)
What caused intermediate depth OMZ’s?
Reduced ventilation and high respiration rates of settling organic matter produced at surface waters.
What is OMZ’s important for?
Although a small% of global ocean they are a significant sink for nitrogen 30-50% N removal in the oceans.
How is Nitrogen removed in the OMZ nitrogen sink?
Denitrification (Dissolved nitrogen being reduced to nitrogen gas by bacteria).
What are OMZ’s an important source of and how?
Greenhouse gases as a by product of respiration (CO2) and denitrification (N20).
Why are the oceans not anoxic?
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)
How to tell is an O2 profile is simply to do with mixing
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)
Why are concentrations of O2 in Atlantic deep waters generally greater than in the Pacific?
Because Atlantic deep waters have more recently left the sea surface so have had less time to lose O2 to oxidation of organic matter.
What is different about CO2 in terms of solubility in water?
It is very soluble in cold and warm water
Describe the potential long term problem if CO2 increases?
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.
What is the general alkalinity trend for the Atlantic and pacific oceans?
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
What does dissolution of any material depend on?
The degree of saturation of the solution (seawater)
What are carbonate ion concentrations in seawater mostly determined by, Temp’ or Pressure
Pressure determines higher saturation values of calcite and aragonite over temperature. Therefore abundance a function of depth
Calcite and Aragonite (Carbonates) are more soluble under what conditions?
Low temperature, high pressure - At Depth!
What is the difference between CaCO3 and SiO2 deep sea sediment distribution?
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
What is the Carbonate Lysocline?
Depth at which large decrease in carbonate %
What is carbonate compensation depth?
Depth at which rate of carbonate solution = or exceeds rate of supply
What is carbonate critical depth
Depth below which there is < 10% CaCO3
What is the long terms effects of increase CO2 in oceans
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
