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Flashcards

Global Biogeochemical Cycles

Charlotte Feldman Chemistry 2nd year English 78 cards

Cards in this deck (78)

  1. 1What are the two names for the slow/fast cycles of carbon?1. Biosphere (fast cycle)
    2. Geosphere (slow cycle)
  2. 2What are the two forms of carbon in the cycle?Organic carbon - dissolved and unreactive
    Inorganic Carbon - largest part of the mobile carbon in the cycle.
  3. 3What is the residence time using the steady state approximation?Equation sheet.
    4.
  4. 4What are the two forward and reverse processes that are involved in the carbon long term cycle and keep CO2 in balance?Equation sheet.
    5.
    Weathering removes CO2, and metamorphism reproduces CO2.
    Photosynthesis removes CO2 and respiration reproduces CO2.
  5. 5Give the natural long term carbon cycle.Equation sheet
    6.
  6. 6GIVE THE NATURAL SHORT TERM CARBON CYCLE.Equation sheet
    7.
  7. 7How come energy generation and CO2 reduction to Biomass have an offset effect on other elemental cycles?They can be seen as oxidation/reduction reactions and the flow of electron generates energy ΔG.
  8. 8Give the equations that represent how energy is produced by the flow of electrons both in equilibrium and not in equilibrium.Equation sheet
    8.
  9. 9What is the main source of Organic matter?Photosynthesis
  10. 10What is chemosynthesis and how does it produce organic matter?Chemosynthesis is the production of OM through chemical energy. Chemoautotrophs utilise inorganic compounds as reducing agents and then synthesis OM from CO2.
  11. 11What is nitrification and give the appropriate Equations. Then give the names and processes of all the other processes involved in chemoautrophyNitrification -
    Organisms utilise reducing agents to produce OM from CO2. Nitrification describes the production of a reducing agent from inorganic nitrogen containing compounds
    Equation sheet 9.
  12. 12Give an example where a compound other than oxygen is used as the oxidant to form a reducing agent from inorganic compounds before the production of OM from CO2. What is this process called?Equation sheet 10.
    Methane and SO4 2-.
    ANAEROBIC OXIDATION.
  13. 13As previously mentioned, Photosynthesis is the main source of OM. For this reason we say that photosynthesis is involved in the primary production of OM. GIVE THE EQUATION FOR PHOTOSYNTHESIS.EQUATION SHEET 11.
  14. 14What are the simple redox equations for photosynthesis involved in primary production?Equation sheet 12.
  15. 15What governs primary production?SUNLIGHT - water, depth, season.
    Nutrients available.
    Temperature. ( kinetic energy for collisions and therefore growth rate).
  16. 16What is a tracer for photosynthesis and therefore net primary production (NPP) in OCEANS?Chlorophylls.
  17. 17What is the main governing factor of photosynthesis and primary production in OCEANS?Sunlight
  18. 18What are the main nutrients that govern PP in OCEANS? Give the ratios.Fe : P : N : C
    1 : 2359 :37736 : 250000
  19. 19Why will some regions of the ocean be ''high nutrient but low in chlorophyll'' e.g. southern ocean.IRON is only required in very small proportions for PP but is it still essential.
  20. 20Why isn't iron fertilisation a solution to rising CO2?On the one hand, relives Fe nutrient deficiency and increases the productivity of PP.
    BUT this would mean the biological pump would need to be increased to increase the export of CO2. This has all sorts of biological consequences, such as producing more algae and therefore messing up the marine food chain.
  21. 21What is the main governing factor of photosynthesis and primary production on LAND?Water distribution ( nutrients always available in soil)
  22. 22What is a tracer for photosynthesis and therefore net primary production (NPP) on LAND?Satellite concentrations.
  23. 23What is the main difference between terrestrial and marine OM.Terrestrial OM contains cellulose and lignin which are produced by plants for structure.
  24. 24How do we know that the OM is different? 3 Ways.1. The OM have different compositions and this can be seen in their C/N ratios.
    2. Terrestrial and Marine OM are made up of different lipids.
    3. Stable carbon isotopic compositions.
  25. 25Which out of terrestrial and marine OM is the richest in nitrogen so has the lower C/N ratio?Marine OM.
  26. 26Give two lipids that are different in terrestrial and marine OM?1. Sterols for terrestrial compared to alkenones for marine.
    2. Cyclic acids for terrestrial compared to straight chain acids for marine.
  27. 27What is heterotrophy? Give the Equation.The removal of organic carbon by oxidation. This occurs when organisms cannot synthesise all the organic molecules they require using only inorganic compounds. Instead they oxidise organic carbon to carbon dioxide to yield cellular energy (respiration).
  28. 28What is the most efficient heterotrophic process? Give two equations.aerobic respiration.
    Reverse of photosynthesis 4.
    Reverse of photosynthesis 11.
  29. 29After aerobic oxidation what other processes are involved in heterotrophy?and give the order of these sedimentary processes for the stepwise degradation of OM. (This only rarely happens in the ocean but is common in underlying sediments)Equation sheet 13.
  30. 30How does OM get from ocean surface to deeper oceans?THE BIOLOGICAL PUMP - pumps OM from surface to depth
  31. 31How come some areas of the ocean contain more OM than others?Some degradation processes are more efficient. Travel from the surface to the sediments involves sinking and this depends on the size of the particles. E.g. Larger OM particulates and particulate sinks.
  32. 32What is dissolved inorganic carbon?In the ocean, dissolved inorganic carbon is dissolved CO2. E.g. Respiration returns OM to CO2 and this is dissolved in the ocean.
    Technically TOTAL DIC = [CO2 + H2CO3 + HCO3- + CO3 2- ]
  33. 33By considering the biological pump, draw and explain the vertical depth profiles of DIC, O2, Phosphorous, Nitrate, pH, CO32- and CO2 in the ocean. To do this, you have to consider what the dominant reactions will be at different depths. How would these profiles change if the biological pump was stronger?Equation sheet 14.
    Amplitude of each process increases e.g. there will be more CO2 uptake in photosynthesis and more release in respiration. The profiles are therefore exaggerated.
  34. 34Why does the deep pacific ocean have more CO2?These questions are always about OCEAN CIRCULATION.
    North atlantic --> Indian Ocean --> Pacific.
    In this time OM is being broken down by respiration and so more CO2 is adding to the water column, therefore there is the most CO2 in the Pacific ocean.
  35. 35What is the kinetic reason as to why OM is not completely degraded by respiration as it sinks and travels from the surface down into the deep/deepest oceans?The sediment rate (burial into sediment) is faster than respiration. Also as you go deeper into the ocean, you leave the O2 region and so respiration rate decreases. (however rate of respiration then starts to increase once more when you reach the deepest oceans and anaerobic processes begin.)
  36. 36What other controls on kinetics i.e. on the activation energy explain why OM is not completely degraded by respiration as it sinks and travels from the surface down into the deep/deepest oceans?1. Some compounds are harder to respire (degrade than others)
    2. The larger the surface areas of the mineral, the more carbon that will be preserved.
  37. 37Give the order of increasing difficulty of degradation for various OM types.Carbohydrates.
    Proteins.
    Lipids.
    Lignin.
    Algaenan
  38. 38What governs reactivity of these different OM types?LaRowe and van Cappellen argue
    it is thermodynamics.
  39. 39What have models of OM degradation revealed? 2 Things.1. There are Multiple pools of OM and over time OM gets harder and harder to degrade.
    2. Labile components are degraded first and this leave a less reactive residual pool.
  40. 40. Describe why a power law or multi-G model of organic matter degradation is better than single-G model.A single 1G model assumes a single kinetic rate constant for OM degradation. However OM is comprised of multiple pools of OM with widely varying reactivity, such that a model that incorporates a range of pools with different kinetic parameters is a more realistic representation. The power law model is the best model because it also account for changes over time as it is expresses degradability as a function of time.
  41. 41What happens to OM during the degradation process? 2 things and why.1. The composition of the OM changes.
    2. The quality of OM becomes poorer (less functionalised)
    Because the more labile components are degraded first , leaving the less labile components behind.
  42. 42Define Diagenesis.The physical and chemical changes that occur during the conversion of sediment to sedimentary rock.
  43. 43Summarise Diagenesis. Two things.Before remineralisation to CO2 ( OM degradation )
    1. Some of the OM will be preserved largely intact. This process is called selective preservation because some species are better preserved than others because because they are harder to degrade ( less reactive.)
    2. In addition some OM is altered before remineralisation to CO2. This is due to interactions amongst compounds and also due to interactions with other inorganic species.
  44. 44Use a flow chart to summarise how OM is mostly returned to DIC by respiration during PP.Flow Chart.
    Equation Sheet.
    15.
  45. 45What are the two components responsible for breaking down OM into methane?Terrestrial biota and surface sediment.
  46. 46What two processes produce methane?Equation sheet 16.
    Methanogenesis and CO2 reduction.
  47. 47what species is responsible for the production of methane by methanogenesis?Archea called methanogens are responsible for the production of methane by methanogenesis.
  48. 48Where does methanogenesis occur?Anoxic sediments and basisn. It is a form of anaerobic respiration that occurs when O2 has ran out.
  49. 49Why is OM degradation ( respiration) into methane by methanogenesis much more prominent into terrestrial settings than marine?The substrates for CH4 formation are different for the marine and terrestrial settings.
    Marine - CO2, Carbonate.
    Terrestrial - acetate (OM)
    This is to do with the different processes of methane oxidation and also the substrate of methane. In the marine setting, carbonate is found low down in the sediments so CH4 is produced here. Here there is no oxygen and so anaerobic oxidation of CH4 is likely and the CH4 produced doesn't actually reach the atmosphere.
    In the terrestrial setting, acetate is found higher up at the surface. The methane reaches the process as a result and a proportion is oxidised via an aerobic process instead.
  50. 50Explain the anaerobic process of methane that is occurring in marine using Equations.Sulphate is the main terminal electron acceptor for the anaerobic oxidation of methane.
    However there is also methanotropic bacteria working together with sulfate that also anerobically oxidises methane.
    Equation sheet 17.
  51. 51How do we study the anaerobic oxidation of methane by methanotrophs (-> not sulphur) in marine settings?SHORTENED TO AOM. Anerobix oxidation by methanotrophs. Can be studied by the stable isotopic compositions e.g. δ13C values and via labelling through fluorescence.
  52. 52In addition to the anaerobic oxidation of CH4 in marine what other process is occuring that prevents the CH4 from reaching the atmosphere?Methane in marine sediment is sequestered by gas hydrates. Large amounts of methane gets tapped within a crystal lattice.
    Hydrates only form under very cold and high pressure conditions.
  53. 53For methane in a terrestrial setting. Give the equation for its aerobic oxidation.Equation sheet 18.
  54. 54Give the three equations that make up the total of dissolved inorganic carbon. Give the total for DIC.Equation sheet 19.
    Total DIC = CO2 + H2CO3 + HCO3 + CO3 2-
  55. 55What are the concentration of the anions of DIC known as and what are their role?Alkalinity.
    The ability of water to resist pH.
    Ocean sea water has a slight net positive charge in general. Ocean pH is maintained by the net charge balance of +ve/-ve ions.
    -ve ions remove H+.
    The DIC anions are able to remove H+ because they exist in more than one charge state.
  56. 56What happens when CO2 is dissolved in ocean sea water? But what do the DIC anions ALREADY PRESENT do ?Acidifies sea water. BUT THE DIC ALREADY PRESENT act as a buffer.
    i.e. the anions restore the original pH of the water on addition of CO2. The presence of buffering materials help
    neutralize acids as they are added to the water
  57. 57Give the carbonate alkalinity equation.Equation sheet 21.
  58. 58Give the two forms of calcium carbonate.Equation sheet 22.
    Biogenic and abiogenic/inorganic form.
  59. 59When do you see abiogenic calcium carbonate in water ?Abiogenic carbonate, the inorganic solid form. Is only seen in water in rare occasions. Where circulation in water is restricted and so the water becomes supersaturated with calcium carbonate and undergoes calcium carbonate precipitation.
  60. 60Give the equilibrium equations that connect biogenic and abiogenic calcium carbonate with organic and inorganic carbon.Equation sheet 23.
  61. 61What happens to the cycles when calcium precipitate dissolution decreases.LEARN.
    24.
  62. 62What happens to the cycles when CO2 in increased?LEARN.
    25.
    x
  63. 63By considering the biological pump, draw and explain the vertical depth profiles of DIC, O2, pH, CO32- and CO2 in the ocean. To do this, you have to consider what the dominant reactions will be at different depths.Equation sheet. 26.
  64. 64What controls calcium carbonate dissolution and why?For calcium carbonate dissolution there is a solubility constant that is temperature and pressure dependent because calcium carbonate dissolution is an equilibrium.
  65. 65What three terms label the variation of calcium carbonate dissolution with depth and define them.Saturation horizon - where carbonate should begin to dissolve.
    Lysocline - Where carbonate actually begins to dissolve. ( calcium carbonate dissolution faster than respiration rate)
    Carbonate compensation depth (CCD) - rain rate = dissolution rate ; i.e. no carbonate sediments beneath this depth.
  66. 66Draw the graph to show how Lysocline and CCD define where in the ocean CaCO3 dissolves or precipitates.Equation sheet 27.
  67. 67How does ocean circulation affect the lysocline?Ocean circulation North atlantic - Antartic - Pacific. Therefore at each stage more respiration occurs. More CO2 dissolved. More CO2 means less CaCO3 and so dissolution will decrease.
  68. 68Why is the lysocline shallower in the Pacific Ocean?Shallower = Quicker rate of dissolution. Although the water circulation means respiration has occurred at each stage so you would think that Pacific ocean has more CO2. Due to the increase in man made CO2, which has started only in the last 60-80 years this CO2 has not yet been transferred to the Pacific Ocean. In addition, Pacific ocean already has a high content of CO2 so does not take up CO2 as easily as the Atlantic. Therefore at this stage, Pacific Ocean has less CO2. Therefore there is more CaCO3 and the rate of dissolution is faster.
  69. 69What is the saturation state?Concentration of ions in solution relative to that required for precipitation. Low saturation state means that a solution is undersaturated and the mineral phase will dissolve.
  70. 70Give the two ways of measuring the saturation state.Equation sheet
    28.
  71. 71Give a short-term and the long-term effects of their being more CO2 (anthropogenic) man made. I.e. Explain why we need seawater/ecosystem monitoring and also CO2 mitigation.Short-term : Less CaCO3
    BUT more OM production through photosynthesis.
    Long term: Organisms cannot calcify. (shells dissolve). -> not fully dependent on CO2 also on temperature, nutrients and sea-level change and mainly less sunlight getting to the coral so less energy produced.
    Very bad for coral reefs made up of aragonite. In turn this is bad for fish as they use coral reefs for shelter and food.
    Long term CO2 uptake cycles- weathering and and photosynthesis. Less CaCO3 means less weathering. Leaves more CO2 to act as Greenhouse gas, temperature of environment increases and large impact on ecosystems.
  72. 72How come the effects of decreasing pH on the waters through CO2 increase and subsequent lowering of CaCO3 only affects shell calcification of some species?Two forms of calcium carbonate. Aragonite and Calcite. Same chemical formula but atoms stacked in different configurations. Calcite is more stable to dissolution with its trigonal structure. Argonite is less stable with its dipyradimal structure. So only species that have shells made out of Argonite get badly affected.
  73. 73What is the UK's largest terrestrial carbon pool?The peatlands.
  74. 74What are active peatlands? Explain through equations.A net carbon sink --> ( CO2 uptake via photosynthesis dominates) and methane source. Rememeber terrestrial's substrate for methane is carbonate which oxidises only at the surface so reaches the atmosphere.
    Photosynthesis
    Methanogenesis
    Hydrogen Fermentation (reverse dominates)
    29 Equation sheet.
  75. 75What are the consequences of falling water levels on Organic matter?Lots of oxidation in peatlands. More aerobic respiration and therefore release of CO2 emissions. Carbon source. And greenhouse gas causing temperature increase as a result.
  76. 76Give a diagram for soil and permafrost.Equation sheet 30.
  77. 77What is the importance of Permafrost?Support's structures.
  78. 78What is the consequence of draining Peatlands on Permafrost?More aerobic oxidation and release of CO2. Greenhouse gas warms the environment. Permafrost melts and this deepens the active layer causing coastal erosion. In addition permafrost contains the methane hydrates and so melting the Permafrost releases methane into the environment. An even worst greenhouse gas. (Positive feedback)

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2nd year Chemistry (Computational Chemistry) Flashcards on Global Biogeochemical Cycles, created by Charlotte Feldman on 15/05/2017.
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