Lecture 16 Carbon Cycle NPS

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Lecture 16 Carbon Cycle NPS Powered By Docstoc
					Global Carbon Cycle
     Why study the C cycle?
• Key element of life – so fundamental
  – Fossil fuel burning and global warming
• Perturbation by humans (atm CO2)
• Complex cycle – long & short term cycles;
  organic and inorganic components
• Geological processes operating over millions of
  years
• Biological processes operating on annual time
  scales
• Interactions between long and short term cycles
“short”-term

“long”-term

anthropogenic
      Combined Inventories
                                        Major Inventories
Atmosphere           770 Gt C   •Majority of C tied up in rock
Terr. Systems     ~2400 Gt C    cycles – large reservoirs with
Oceans           ~39,000 Gt C   long residence times
Sed. Rocks    50,000,000 Gt C   •Reservoirs active on short time
                                scales are ocean, atm, & land
                                •Large exchange fluxes to and
                                from atm – atm has short
                                residence time (3 yr); small net
                                fluxes due to biology (most PP is
                                respired)
                                •Problem with adding fossil fuel
                                CO2 to atm – transferring C
                                from long term geologic
                                reservoir to a short term
                                reservoir – may affect short
                                term feedback control
                                mechanisms




  Fig. 8-3
                                             Atmospheric CO2                               50.3

                                                                                 Respiration      Air-Sea Exchange
                         Terrestrial primary
                         production and respiration                                                     50
                                                                    POC                    CO2
            Physical
                         59.6 - 59.7                                  Marine primary prod.
            weathering                       River transport
                                        60          0.4                                         Upwelling
                                                                               remineralization
           Kerogen             Land Plants                     Particle Rain


                                                                               Oceans
                                                                POC Deposition            CO2
                               Humification

                                                                                               Benthic Fluxes
      Uplift of                Soil humus
  sedimentary     0.1
                                                                        Recent Sediments
        rocks


                                                                  0.1   Carbon Burial



                                       Sedimentary Rocks


A model – little transfer of biological C to ocean (from land) or sediments (from water)
               Atmosphere
• Most C in atm as CO2
  – Some methane and CO
• Atm CO2 shows rapid increase in recent
  time
  – Beginning with Industrial Revolution
• See seasonal variations in recent
  increase
  – Uptake in Spring due to plant growth (N hemisphere)
  – Release in fall from net respiration
     Northern hemisphere
     -More land
     -More terrestrial prod

Figs. 1-2 and 1-3
                Southern amplitude is lower
                Seasonality offset by 6 mos.




Northern hemisphere has more extensive seasonal forests
Close tracking between N & S hemispheres
    Prior to humans, the system showed natural variability
               (50 – 80 ppm glacial-interglacial)
Interglacial      Smaller Holocene changes

                                               Glacial
        Holocene changes
• Recent high resolution ice core
• Natural variability in Holocene is second
  order change when compared with
  glacial-interglacial excursions and
  anthropogenic increase
• Allows us to think about a nearly
  constant pre-industrial interglacial CO2
  level of ~280 ppm
 Recent increases in Atm CO2
• Some due to land use changes (pre-
  industrial)
  – Deforestation – two-fold problem
     • Decrease PS uptake of CO2
     • Burn the wood - charcoaling
• Mainly due to fossil fuel burning (post-
  industrial)
• Deforestation in tropics may be partially
  balanced by N hemisphere forest
  expansion/regrowth
               Atmos. increase   IPCC – Intergovernmental Panel on Climate Change
                  (3.3 PgC/yr)


                                                        Land use change (1.7 PgC/yr)
Emissions                                               Residual terrestrial sink
(5.5 PgC/yr)               Atmosphere                   (1.9 PgC/yr)


                                                          Ocean uptake (2 PgC/yr)
                                               Atmosphere                  ∆pCO2 < 0
                                                                           (primarily high latitudes)
                 ∆pCO2 > 0
       CO2       (primarily upwelling              CO2                              CO2
                 regions)


                  Surface Ocean
                                                                               CO2 + CO32- + H2O ® 2HCO3-
                                 CO2 + H2O ® Organic Matter + O2

                             Ca2+ + 2HCO32- ® CaCO3 + CO2 + H2O


                      CO2 + CO32- + H2O ® 2HCO3-         Sinking particulate
Upwelling                                                organic matter
and vertical mixing                                      (“biological pump”)          Bottom water formation
                                                                                      (high latitudes)
                                          CO2 + H2O ¬ Organic Matter + O2             (“solubility pump”)


                         HCO3-
Deep Ocean                                                          CO2



                                          CO2 + H2O ¬ Organic Matter + O2
                                        Ca2+ + 2HCO32- ¬ CaCO3 + CO2 + H2O
 Sediments
 Oceans are largest “active” reservoir in the carbon cycle – primarily DIC
                    Oceans
• Link the “active” or short-term cycles with long-
  term geological cycles – sink for fossil fuel CO2
• Ocean processes
   – Biological cycle
   – Weathering reactions and long term controls
   – Atm CO2 à riverine bicarb à neutralized in ocean à
     returned to atm or buried in seds
• Processes that remove CO2 from atm
   – Gas exchange – equilibration of sfc ocean with atm
   – Biological pump
   – Bottom water formation
             Gas exchange
• If CO2 were a simple gas, ocean could only
  take up ~3% of fossil fuel input
• Acid-base chemistry enhances ocean uptake
• Remember carbonate buffering system?
  – CO32- + H2O + CO2 à 2 HCO3-
  – Buffering rxn drives CO2 to bicarb
• Surface waters reach equilibrium with atm in
  about 1 year
  – Can keep pace with human activity
  – But surface ocean too small to have capacity to
    remove it all
           Biological Pump
• PP and calcite ppt consume DIC
• Removed from surface ocean via particle flux
• Through interactions with carbonate system,
  this lowers partial pressure (pCO2) in surface
  ocean which enhances gas exchange
  (DpCO2< 0)
• Transports CO2 to deep ocean in the form of
  OM or calcite shells
• Limitations of biological pump
  – Availability of other nutrients (N, P, Fe)
  – More CO2 doesn’t necessarily lead to more PP
    Bottom water formation
• Removes CO2 by physical movement of
  water away from surface
• Solubility pump
• CO2 is more soluble in cold water
 Intermediate and deep water
• Can add CO2 through oxidation of OM
• Calcite dissolution – excess CO2 from
  OM oxidation reacts with sinking calcite
                Upwelling
• Intermediate waters are enriched in DIC
  – Mixing with deep waters, OM oxidation &
    calcite dissolution, yields some CO2
    increase
• Upwelling results in excess pCO2 in
  surface waters (DpCO2 > 0)
  – Oceans outgas CO2
  – High productivity upwelling can still be net
    CO2 sinks
Global oceanic C sources and sinks
for atm C
 - reflect upwelling and deep water formation
and high productivity
        IPCC calculations
• Integrate data on ocean flux data
• Calculation attempts to assess short-
  term sinks for excess atm CO2 due to
  anthropogenic activities
 Time scales of ocean C cyle
• Ocean processes slow relative to rate of fossil
  fuel burning
• Bottom water circulation on timescales of 100’s
  of years so equilibration with atm is slow
• Deep sea seds equilibrate with atm on
  timescales of 1000’s of years – where the bulk
  of the ocean’s neutralizing capacity resides
• Oceans respond too slowly to take up all excess
  CO2 – so atm CO2 is increasing
• But, oceans have helped! Oceans have taken
  up 1/3 to ½ of added CO2
                                                Atmosphere                   ∆pCO2 < 0
                                                                             (primarily high latitudes)
                      ∆pCO2 > 0
          CO2                                                Equilibration
                      (North Pacific and           CO2       time ~1 yr              CO2
                      upwelling regions)


                  Surface Ocean
                                  CO2 + H2O ® Organic Matter + O2              CO2 + CO32- + H2O ® 2HCO3-

                                  Ca2+ + 2HCO32- ® CaCO3 + CO2 + H2O


                      CO2 + CO32- + H2O ® 2HCO3-         Sinking particulate
Upwelling                                                organic matter
and vertical mixing     Equilibration time               (“biological pump”)                Bottom water
                        ~500-1000 yr                                                        formation
                                         CO2 + H2O ¬ Organic Matter + O2                    (high latitudes)


                          HCO3-
Deep Ocean                                                          CO2



                                           CO2 + H2O ¬ Organic Matter + O2
                                       Ca2+ + 2HCO32- ¬ CaCO3 + CO2 + H2O
 Sediments                                                                      Equilibration time
                                                                                ~103-104 yr
          Terrestrial systems
• Variety of reservoirs that turnover on different
  timescales
   – Soil humus – altered remains of plants
   – Land plant biomass
   – Methane – source of atm methane
• Terrestrial PP ~ = to Marine PP
• Terrestrial systems store excess CO2 differently –
  humus versus bicarb
• Imp for understanding system responses to
  increasing CO2. Increasing CO2:
   – might increase PP (neg feedback)
   – might increase rates of decomposition (pos feedback)
                                               Atmospheric CO2                               50.3

                                                                                   Respiration      Air-Sea Exchange
                            Terrestrial primary
                            production and respiration                                                    50
                                                                      POC                    CO2
                           59.6 - 59.7                                  Marine primary prod.
                                               River transport
                   Physical
                   weathering
                                          60                                                      Upwelling
                                                     0.4
                                                                                 remineralization
         Kerogen                 Land Plants                     Particle Rain


                                                                                 Oceans
                                                                  POC Deposition            CO2
                                 Humification

                                                                                                 Benthic Fluxes
    Uplift of                    Soil humus
sedimentary     0.1
                                                                          Recent Sediments
      rocks


                                                                    0.1   Carbon Burial



                                         Sedimentary Rocks



                      Comparable terrestrial & marine PP
 negative feedback
 (temperature and
 CO2 fertilization)
                               positive feedback
                               (temperature enhancement of
                               soil respiration)




Terrestrial system responses
to rising CO2 and global
warming
       Controls on atm CO2
• Break down overall cycle to
  components
• Look at effects on particular
  components
    Short-term biological cycle
• Years to decades
• Does not include calcite ppt/dissolution
• Does not include anthropogenic inputs
• PS versus respiration nearly balanced – little
  loss
• Some transport of org C from land to oceans
    – Most gets oxidized in the ocean
• Small amount of marine OM buried in seds
    – Leaves behind some O2 in atm
• Short-term cycles process a lot of CO2
    - 30-50% of atm CO2 consumed per year
      O2   Net
           productivity




CO2   Organic matter
      O2   Net
           productivity




CO2   Organic matter
                                 O2   Net
                                      productivity


               CO2


Uplift and kerogen    O2
          oxidation

                           CO2   Organic matter
                                 O2   Net
                                      productivity


               CO2

                      O2
Uplift and kerogen
          oxidation

                           CO2   Organic matter
        Long term org C cycles
• Millions of years
• Components include: OM in sediments, fossil fuels,
  atm O2 versus CO2
• Burial of OM from Short-term cycle
  – Inc P and T; most ends up as kerogen,
  – Some winds up in fossil fuels (oil, coal)
  – OM in shale is largest reservoir on earth (long t)
• Removal balanced by kerogen oxidation/weathering
  • Affects atm O2
  – Net burial leaves O2 in the atm
   Also linked to pyrite burial/oxidation which requires OM
   as an intermediate to catalyze the sulfate reduction




          Produced by bacterial sulfate reduction
          - linked to carbon oxidation


O2 in atm controlled by a balance between pyrite and OM
burial in seds and later oxidation on land
Without this balance atm O2 would increase to 150% of present
Levels and depletion of atm CO2 in < 10,000 years (see text)
     Long-term inorg C cycle
• 100’s of millions of years
• Balance between weathering and plate
  tectonics
  – Weathering silicate rocks consumes CO2,
    transferred to the ocean as bicarb, removal of
    bicarb by organisms & calcite, burial in seds,
    subduction, vulcanism (also affects other cations –
    Ca, Mg, Na)
• Cycle is a balance between weathering (takes
  up CO2) and tectonics (releases CO2)
• Plate tectonics – more vigorous then more
  CO2 release
• Climate sensitivity (weathering)
                                                            CO2 removal
                                        Bicarbonate
                                        transport
                           CaCO3 ppt.


                       CaCO3




                                                      (“regenerates” CO2)
     (“regenerates” CO2)




Figs. 8-17
 Short-term




Long term (organ

 Long term
 (inorganic/tecton
Link with short term C cycle
In surface oceans
                                        “adds” back CO2




            Onset of modern plate
            tectonics “turns this on”
Increase in surface temperature due to increase in solar luminosity
Drop in CO2 by increased weathering at higher temp
Decrease greenhouse – increase ppt of carbonates?
Bob Berner’s calculations of changes in CO2 over the Phanerozoic
Bob Berner’s calculations of changes in CO2 over the Phanerozoic




                     “Hot” houses
Bob Berner’s calculations of changes in CO2 over the Phanerozoic




                     “Hot” houses




              “Ice” houses
Fig. 8-18
             Effect of humans
• Pre-industrial
   – Steady state on decadal to century timescales
   – Ocean a net source of CO2
      • Neutralizes river bicarb and oxidation of OM from rivers
   – Burial of org C
      • That which escaped oxidation and marine OM
• Humans
   – Oceans a sink for CO2
   – Increase sediment and nutrient load to
     rivers/ocean
   – Eutrophication, hypoxia, denitrification
Fig. 10-16 A portion of the biogeochemical cycles of inorganic carbon (Cing) and organic carbon (Corg), nutrient N
and P, and suspended solids (SS) in the land–ocean system. (a) Geological, long-term system; (b) one possible
situation today. In (b), the fluxes of organic and inorganic carbon and suspended solids to the seafloor are increased
over their pristine geological values in (a). These increases are due to human activities. Notice the net heterotrophic
nature of the ocean giving rise to a net flux of carbon dioxide to the atmosphere prior to human interference in the
carbon cycle. Now more carbon dioxide enters the ocean because of the burning of fossil fuels and deforestation
practices (see Chapter 12). Fluxes are in millions of tons of C, N, P, and suspended solids per year. (After Wollast
and Mackenzie, 1989.)
All fluxes are millions                                     CO2
of tons of C per year
                                                          460 (net)      100 (net; approx.
                                            360    200                   50,000 (r) - 50,100(pp))
                                oxidation


                          400
        Corg (terr.)

                 Riverine inputs
                                                          The Ocean
                          400
               Cing                         rxn. (1)
                                                                      Corg (marine +terr)
                                                               Burial in sediments

                                                   Cing
                                                  200                       140



         rxn. (1)
         Fossil fuel burning
• Transferring large amounts of CO2 from rock
  cycle to atm with no equivalent rapid uptake
  mechanisms!
  – Ocean uptake limited by the biological pump (nuts)
  – Uptake by terr. systems not rapid enough
  – Accumulates in atm
• How does increase affect climate?
  – Depends on time scales of increase in atm conc
    versus time scales of changes in earth’s heat balance
    (via its circulatory system)
  – Positive and negative feedback responses
N and P Cycles
              80 y-1




Global nitrogen reservoirs, fluxes and turnover times. Major reservoirs are underlined, pool
sizes and fluxes are given in Tg (1012 g) N and Tg N yr-1. Turnover times (reservoir divided
by largest flux to or from reservoir ) are in parentheses.
                     Atmosphere



120 (NF)         98 (DN)                      121 (NF)
                                 172 (DN)




                           27 (RT)
   Land                              Oceans



The Pre-Industrial N Cycle (fluxes = Tg N/yr)
    (1860’s numbers from Galloway et al., 2004)
Greenhouse effect   Ice volume
                                       Global sea level




 Atmospheric CO2
                                      Area of continental
                                      shelves
                       (+)


  Oceanic primary
  productivity                        Shelf denitrification




                    Oceanic fixed-N
                    inventory
                      Stimulates N-fixation




Fig. 14-13 The iron fertilization hypothesis for the intensification of the biological pump
during glaciations.
                                                                 Atmosphere                        Stratospheric
                                                                                                      Effects
                                                                                 PM &
                                                     Ozone
              NOx                                                              Visibility                  GH
                                                     Effects                                              Effect
                                                                                Effects
                                                                                                            s
    Energy
   Productio                                                                                            N 2O
       n                                                                            Terrestrial
                                                         NOx                        Ecosyste
                                                                 NH3
      Food                                                                             ms
                                          NHx    Agroecosystem Effects
   Production                                                                  Forests &
                                                  Crop      Animal             Grassland
    People                                               Soil                     Soil
 (Food; Fiber)
                                          Norg             NO3
                                                                                                        N 2O

                                                                 Groundwater
 Human Activities                                                   Effects



The Nitrogen                                         Surface water
                                                        Effects
                                                                                         Coastal
                                                                                         Effects
                                                                                                      Ocean
                                                                                                      Effects

  Cascade
  --Indicates denitrification potential                                                  Aquatic Ecosystems
                                                             Anthro. N fixation = 140 Tg N/yr
                                                                                         - 41
                                                                                        - 8.5
                                              (t ≈ 100 yr)                                 -9
                                                                                         -3.4
                                                                                 61.9 Tg N/yr

                                                                      ~80 Tg N/yr missing ?
                  3.4 x (14 to 32) = 50-110




Retained in soils or denitrified
(?)
Nr and the Atmosphere
            u NOx emissions contribute to OH,
              which defines the oxidizing
              capacity of the atmosphere
            u NOx emissions are responsible for
              tens of thousands of excess-deaths
              per year in the United States
            u O3 and N2O contribute to
              atmospheric warming
            u N2O emissions contribute to
              stratospheric O3 depletion
Nr and Freshwater Ecosystems
               •   Surface water acidification
                    – Tens of thousands of lakes
                      and streams
                    – Biodiversity losses


               •   As reductions in SO2
                   emissions continue, Nr
                   deposition becomes more
                   important.
Nr and Coastal Ecosystems
           • Increased algal productivity
           • Shifts in community structure
           • Harmful algal blooms
           • Degradation of seagrass and algal
             beds
           • Formation of nuisance algal mats
           • Coral reef destruction
           • Increased oxygen demand and
              hypoxia
           • Increased nitrous oxide (greenhouse
              gas)

                                            Sybil Seitzinger, 2003
    There are significant effects
   of Nr accumulation within each
             reservoir




These effects are linked temporally
   and biogeochemically in the
        Nitrogen Cascade
                                                 Atmosphere




                                                              Terrestrial
                                                              Ecosyste
               Food                                              ms
                           NHx    Agroecosystem Effects
            Production
                                   Crop      Animal
           People                         Soil
        (Food; Fiber)
                           Norg



        Human Activities


  The Nitrogen
    Cascade
Galloway et al., 2003a
                                                                Aquatic Ecosystems
                                                 Atmosphere
                                                                 PM &
                                                               Visibility
                                                                Effects



                                                                    Terrestrial
                                                                    Ecosyste
                                                  NH3
               Food                                                    ms
                           NHx    Agroecosystem Effects
            Production                                         Forests &
                                   Crop      Animal            Grassland
           People                         Soil                    Soil
        (Food; Fiber)
                           Norg



                                                 Groundwater
        Human Activities                            Effects



  The Nitrogen                        Surface water
                                         Effects
                                                                         Coastal
                                                                         Effects
                                                                                   Ocean
                                                                                   Effects

    Cascade
Galloway et al., 2003a
                                                                         Aquatic Ecosystems
                                                  Atmosphere
                                                                  PM &
                                                                Visibility
                                                                 Effects



                                                                     Terrestrial
                                                                     Ecosyste
                                                  NH3
               Food                                                     ms
                           NHx    Agroecosystem Effects
            Production                                          Forests &
                                   Crop      Animal             Grassland
           People                         Soil                     Soil
        (Food; Fiber)
                           Norg             NO3


                                                  Groundwater
        Human Activities                             Effects



  The Nitrogen                        Surface water
                                         Effects
                                                                          Coastal
                                                                          Effects
                                                                                    Ocean
                                                                                    Effects

    Cascade
Galloway et al., 2003a
                                                                          Aquatic Ecosystems
                                                      Atmosphere
                                                                      PM &
                                          Ozone
                         NOx                                        Visibility
                                          Effects
                                                                     Effects
             Energy
            Productio
                n                                                        Terrestrial
                                              NOx                        Ecosyste
                                                      NH3
               Food                                                         ms
                               NHx    Agroecosystem Effects
            Production                                              Forests &
                                       Crop      Animal             Grassland
           People                             Soil                     Soil
        (Food; Fiber)
                               Norg             NO3


                                                      Groundwater
        Human Activities                                 Effects



  The Nitrogen                            Surface water
                                             Effects
                                                                              Coastal
                                                                              Effects
                                                                                        Ocean
                                                                                        Effects

    Cascade
Galloway et al., 2003a
                                                                              Aquatic Ecosystems
                                                                 Atmosphere
                                                                                 PM &
                                                     Ozone
              NOx                                                              Visibility
                                                     Effects
                                                                                Effects
    Energy
   Productio
       n                                                                            Terrestrial
                                                         NOx                        Ecosyste
                                                                 NH3
      Food                                                                             ms
                                          NHx    Agroecosystem Effects
   Production                                                                  Forests &
                                                  Crop      Animal             Grassland
    People                                               Soil                     Soil
 (Food; Fiber)
                                          Norg             NO3


                                                                 Groundwater
 Human Activities                                                   Effects



The Nitrogen                                         Surface water
                                                        Effects
                                                                                         Coastal
                                                                                         Effects
                                                                                                   Ocean
                                                                                                   Effects

  Cascade
  --Indicates denitrification potential                                                  Aquatic Ecosystems
                                                                 Atmosphere                        Stratospheric
                                                                                                      Effects
                                                                                 PM &
                                                     Ozone
              NOx                                                              Visibility                  GH
                                                     Effects                                              Effect
                                                                                Effects
                                                                                                            s
    Energy
   Productio                                                                                            N 2O
       n                                                                            Terrestrial
                                                         NOx                        Ecosyste
                                                                 NH3
      Food                                                                             ms
                                          NHx    Agroecosystem Effects
   Production                                                                  Forests &
                                                  Crop      Animal             Grassland
    People                                               Soil                     Soil
 (Food; Fiber)
                                          Norg             NO3
                                                                                                        N 2O

                                                                 Groundwater
 Human Activities                                                   Effects



The Nitrogen                                         Surface water
                                                        Effects
                                                                                         Coastal
                                                                                         Effects
                                                                                                      Ocean
                                                                                                      Effects

  Cascade
  --Indicates denitrification potential                                                  Aquatic Ecosystems
                                  Ind. N fix.

Population
                                Crop N fix.
             Total react. N

                              Fossil fuel N F
Fig. 10-16 A portion of the biogeochemical cycles of inorganic carbon (Cing) and organic carbon (Corg), nutrient N
and P, and suspended solids (SS) in the land–ocean system. (a) Geological, long-term system; (b) one possible
situation today. In (b), the fluxes of organic and inorganic carbon and suspended solids to the seafloor are increased
over their pristine geological values in (a). These increases are due to human activities. Notice the net heterotrophic
nature of the ocean giving rise to a net flux of carbon dioxide to the atmosphere prior to human interference in the
carbon cycle. Now more carbon dioxide enters the ocean because of the burning of fossil fuels and deforestation
practices (see Chapter 12). Fluxes are in millions of tons of C, N, P, and suspended solids per year. (After Wollast
and Mackenzie, 1989.)
Sulfur cycle
Nr and Terrestrial Ecosystems

               •   N is the limiting nutrient in most
                   temperate and polar
                   ecosystems

               •   Nr deposition increases and then
                   decreases forest and grassland
                   productivity

               •   Nr additions probably decrease
                   biodiversity across the entire range
                   of deposition
                            Sulfate



Pyrite uplift and
weathering

                    Pyrite burial
                                      Hydrothermal
                                      uptake
                          Sulfate




       SO2

                    DMS
H 2S         H 2S
                                SO2
                                Sulfate




       SO2   SO2

                          DMS
H 2S
                                      SO2
                   H 2S
William Turner, “The fighting Téméraire tugged
to her last berth to be broken up” (Tambora)




                   Ash and debris
                   from volcanic
                   eruptions




                                                 Edvard Munch “The Scream”
                                                 (possibly inspired by Krakatoa)
                 The CLAW Hypothesis


                (neg. feedback; reflectivity)
 Clouds                                            Temp.


(+)
                                                       ? (+/-)
  Cloud condensation
  nuclei



          (+)
                              (+)               Plankton
            DMS
Fig. 14-18




             Fig. 14-19

				
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