Block 10: Organic Carbon Flashcards
(28 cards)
What is the basic reaction underlying the carbon cycle? Which 2 processes does it contain?
CO2 + H2O + energy <> O2 + CH2O
The forward reaction is the reduction of CO2 to form organic carbon (photosynthesis)
The backward reaction is the oxidation of CH2O to form inorganic carbon (respiration)
What are organic compounds?
Compounds made from at least one C-H bond with an oxidation state under +4
What are saturated & unsaturated organic compounds?
Saturated compounds have single carbon-carbon bonds (maximising number of attached hydrogens), with every carbon making 4 bonds
What are hydrocarbons?
Molecules made from C-C & C-H bonds only
What is the different between alkanes, cycloalkanes, & alkenes?
Alkanes are saturated chains (CnH2n+2)
Cycloalkanes are saturated rings (CnH2n)
Alkenes contain at least 1 unsaturated bond
How are complex compounds formed?
A functional group is attached to a chain or ring, imparting characteristics of solubility, toxicity, volatility, & reactivity
Are organic compounds soluble in water?
Typically not, but increased solubility results from many functional groups containing O, N, & Cl
What are aromatic hydrocarbons?
Cyclic hydrocarbons with delocalised ∂ & π bonds
What are phenols?
Compounds derived from benzene rings by the addition of at least one hydroxyl group in place of a hydrogen atom
What are long-chain perfluorinated chemicals?
Compounds containing hydrophobic C-F bonds at the tail & hydrophilic functional groups at the head
What are the simplest complex organic compounds & how are they made?
Carbohydrates are hydrophilic organic compounds made directly from autotrophs, primarily from C, O, H
Monomer: monosaccharide
Polymer: polysaccharide
What are proteins?
Chains of amino acids (polypeptides) combined with functional groups, complexly folded upon themselves
Monomer: amino acid
Polymer: polypeptide
What are lipids?
Hydrophobic organic compounds formed primarily from C, O, H with a high H:O ratio
Monomer: fatty acids, glycerol, etc.
Polymer: triglycerides, phospholipids, etc
What is the Redfield Ratio?
The roughly constant C:N:P molar ratio of 106:16:1 in marine biomass
What are the 3 primary steps involved in the marine biological pump?
- POC production lowers surface ocean DIC
- More atmospheric CO2 dissolves in surface seawater due to disequilibrium
- POC is exported to the deeper ocean & decomposes back into CO2 to create a DIC gradient, increasing with depth
How is sediment organic matter cycled through diagenesis?
Aerobic oxidation consumes O2, triggering redox cascades until OM takes over as the oxidant in fermentation. Once all labile OM & oxidants are consumed, pressure from sediment accumulation will form kerogen, some of which will form hydrocarbons
What is shown by the van Krevelen plot?
The depletion of hydrogen & oxygen in organic matter with maturity during kerogen diagenesis
How does soil primary production differ from marine primary production?
Constant erosion occurring from the top of the profile & unsaturated zone provides a higher supply of O2
What is the octanol-water partition coefficient?
Kow compares a compound’s solubility in octanol vs water. High values indicate hydrophobic materials that prefer organic matter, & therefore bioaccumulation
What are bioaccumulation, bioconcentration, & biomagnification?
Bioaccumulation: the incorporation of a substance into an organism with lower rate of removal than intake
Bioconcentration: bioaccumulation with absorption rather than ingestion
Biomagnification: bioaccumulation across trophic levels
How do the behaviours of light & dense non-aqueous phase liquids differ?
Light NAPLs are water insoluble compounds (e.g. octane) that tend to fill pores between sediment grains, with some dissolving into aquifers below the water table
Dense NAPLs are water insoluble compounds (e.g. chlorinated hydrocarbons) that sink to the bottom of aquifers & seep deeper through fractures in confining layers
Which 4 major fluxes control pCO2?
Silicate weathering (inorganic sink), sulphide/carbonate weathering (inorganic source), organic carbon burial (organic sink), & rock organic carbon oxidation (organic source)
What are the dominant positive & negative CO2 feedback systems?
Positive: cooling creates ice growth, increasing albedo, promoting cooling; warming creates ice melt, lowering albedo, promoting warming
Negative: cooling decreases weathering, increasing GHG emissions, causing warming; warming increases weathering, decreasing GHG emissions, causing cooling
How does erosion drive the OC cycle & weathering?
Erosion causes higher biological OC export & offshore burial, creating higher concentrations of OC petrol
Erosion causes higher exposure of fresh primary minerals; silicates create a sink, carbonates & sulphides a source
