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Global Carbon Cycle. Why study the C cycle? Key element of life – so fundamental –Fossil fuel burning and global warming Perturbation by humans (atm CO.

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Presentation on theme: "Global Carbon Cycle. Why study the C cycle? Key element of life – so fundamental –Fossil fuel burning and global warming Perturbation by humans (atm CO."— Presentation transcript:

1 Global Carbon Cycle

2 Why study the C cycle? Key element of life – so fundamental –Fossil fuel burning and global warming Perturbation by humans (atm CO 2 ) 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

3 “short”-term “long”-term anthropogenic

4 Fig. 8-3 Combined Inventories Atmosphere 770 Gt C Terr. Systems ~2400 Gt C Oceans ~39,000 Gt C Sed. Rocks 50,000,000 Gt C Major Inventories 1.Majority of C tied up in rock cycles – large reservoirs with long residence times 2.Reservoirs active on short time scales are ocean, atm, & land 3.Large exchange fluxes to and from atm – atm has short residence time (3 yr); small net fluxes due to biology (most PP is respired) 4.Problem with adding fossil fuel CO 2 to atm – transferring C from long term geologic reservoir to a short term reservoir – may affect short term feedback control mechanisms

5 Atmospheric CO 2 KerogenLand Plants Soil humus Humification Sedimentary Rocks Uplift of sedimentary rocks Particle Rain Oceans Recent Sediments POC POC Deposition Carbon Burial CO 2 Marine primary prod. Benthic Fluxes Air-Sea Exchange Terrestrial primary production and respiration River transport Respiration 50 0.1 50.3 59.6 - 59.7 60 0.1 CO 2 remineralization Upwelling Physical weathering 0.4 A model – little transfer of biological C to ocean (from land) or sediments (from water)

6 Atmosphere Most C in atm as CO 2 –Some methane and CO Atm CO 2 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

7 Figs. 1-2 and 1-3 Northern hemisphere -More land -More terrestrial prod

8 Southern amplitude is lower Seasonality offset by 6 mos. Northern hemisphere has more extensive seasonal forests Close tracking between N & S hemispheres

9 Prior to humans, the system showed natural variability (50 – 80 ppm glacial-interglacial) Smaller Holocene changes Glacial Interglacial

10 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 CO 2 level of ~280 ppm

11 Recent increases in Atm CO 2 Some due to land use changes (pre- industrial) –Deforestation – two-fold problem Decrease PS uptake of CO 2 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

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13 Atmosphere Emissions (5.5 PgC/yr) Atmos. increase (3.3 PgC/yr) Ocean uptake (2 PgC/yr) Land use change (1.7 PgC/yr) Residual terrestrial sink (1.9 PgC/yr) IPCC – Intergovernmental Panel on Climate Change

14 Atmosphere Surface Ocean Deep Ocean Sediments CO 2 ∆pCO 2 > 0 (primarily upwelling regions) ∆pCO 2 < 0 (primarily high latitudes) CO 2 + CO 3 2- + H 2 O  2HCO 3 - Upwelling and vertical mixing Sinking particulate organic matter (“biological pump”) CO 2 + H 2 O  Organic Matter + O 2 CO 2 + CO 3 2- + H 2 O  2HCO 3 - CO 2 + H 2 O  Organic Matter + O 2 Ca 2+ + 2HCO 3 2-  CaCO 3 + CO 2 + H 2 O CO 2 HCO 3 - Bottom water formation (high latitudes) (“solubility pump”) Ca 2+ + 2HCO 3 2-  CaCO 3 + CO 2 + H 2 O CO 2 + H 2 O  Organic Matter + O 2 Oceans are largest “active” reservoir in the carbon cycle – primarily DIC

15 Oceans Link the “active” or short-term cycles with long-term geological cycles – sink for fossil fuel CO 2 Ocean processes –Biological cycle –Weathering reactions and long term controls –Atm CO 2  riverine bicarb  neutralized in ocean  returned to atm or buried in seds Processes that remove CO 2 from atm –Gas exchange – equilibration of sfc ocean with atm –Biological pump –Bottom water formation

16 Gas exchange If CO 2 were a simple gas, ocean could only take up ~3% of fossil fuel input Acid-base chemistry enhances ocean uptake Remember carbonate buffering system? –CO 3 2- + H 2 O + CO 2  2 HCO 3 - –Buffering rxn drives CO 2 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

17 Biological Pump PP and calcite ppt consume DIC Removed from surface ocean via particle flux Through interactions with carbonate system, this lowers partial pressure (pCO 2 ) in surface ocean which enhances gas exchange (  pCO 2 < 0) Transports CO 2 to deep ocean in the form of OM or calcite shells Limitations of biological pump –Availability of other nutrients (N, P, Fe) –More CO 2 doesn’t necessarily lead to more PP

18 Bottom water formation Removes CO 2 by physical movement of water away from surface Solubility pump CO 2 is more soluble in cold water

19 Intermediate and deep water Can add CO 2 through oxidation of OM Calcite dissolution – excess CO 2 from OM oxidation reacts with sinking calcite

20 Upwelling Intermediate waters are enriched in DIC –Mixing with deep waters, OM oxidation & calcite dissolution, yields some CO 2 increase Upwelling results in excess pCO 2 in surface waters (  pCO 2 > 0) –Oceans outgas CO 2 –High productivity upwelling can still be net CO 2 sinks

21 Global oceanic C sources and sinks for atm C - reflect upwelling and deep water formation and high productivity

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23 IPCC calculations Integrate data on ocean flux data Calculation attempts to assess short-term sinks for excess atm CO 2 due to anthropogenic activities

24 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 CO 2 – so atm CO 2 is increasing But, oceans have helped! Oceans have taken up 1/3 to ½ of added CO 2

25 Atmosphere Surface Ocean Deep Ocean Sediments CO 2 CO 2 + H 2 O  Organic Matter + O 2 Ca 2+ + 2HCO 3 2-  CaCO 3 + CO 2 + H 2 O ∆pCO 2 > 0 (North Pacific and upwelling regions) ∆pCO 2 < 0 (primarily high latitudes) CO 2 + CO 3 2- + H 2 O  2HCO 3 - Upwelling and vertical mixing Sinking particulate organic matter (“biological pump”) CO 2 + H 2 O  Organic Matter + O 2 CO 2 + CO 3 2- + H 2 O  2HCO 3 - CO 2 + H 2 O  Organic Matter + O 2 Ca 2+ + 2HCO 3 2-  CaCO 3 + CO 2 + H 2 O CO 2 HCO 3 - Bottom water formation (high latitudes) Equilibration time ~1 yr Equilibration time ~500-1000 yr Equilibration time ~10 3 -10 4 yr

26 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 CO 2 differently – humus versus bicarb Imp for understanding system responses to increasing CO 2. Increasing CO 2 : –might increase PP (neg feedback) –might increase rates of decomposition (pos feedback)

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28 Atmospheric CO 2 KerogenLand Plants Soil humus Humification Sedimentary Rocks Uplift of sedimentary rocks Particle Rain Oceans Recent Sediments POC POC Deposition Carbon Burial CO 2 Marine primary prod. Benthic Fluxes Physical weathering Air-Sea Exchange Terrestrial primary production and respiration River transport Respiration 50 0.4 0.1 50.3 59.6 - 59.7 60 0.1 CO 2 remineralization Upwelling Comparable terrestrial & marine PP

29 negative feedback (temperature and CO 2 fertilization) positive feedback (temperature enhancement of soil respiration) Terrestrial system responses to rising CO 2 and global warming

30 Controls on atm CO 2 Break down overall cycle to components Look at effects on particular components

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32 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 O 2 in atm Short-term cycles process a lot of CO 2 - 30-50% of atm CO 2 consumed per year

33 Organic matter O2O2 Net productivity CO 2

34 Organic matter O2O2 Net productivity CO 2

35 Organic matter O2O2 Net productivity CO 2 O2O2 Uplift and kerogen oxidation

36 Organic matter O2O2 Net productivity CO 2 O2O2 Uplift and kerogen oxidation

37 Long term org C cycles Millions of years Components include: OM in sediments, fossil fuels, atm O 2 versus CO 2 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  ) Removal balanced by kerogen oxidation/weathering Affects atm O 2 –Net burial leaves O 2 in the atm

38 Produced by bacterial sulfate reduction - linked to carbon oxidation Also linked to pyrite burial/oxidation which requires OM as an intermediate to catalyze the sulfate reduction O 2 in atm controlled by a balance between pyrite and OM burial in seds and later oxidation on land Without this balance atm O 2 would increase to 150% of present Levels and depletion of atm CO 2 in < 10,000 years (see text)

39 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 CO 2 ) and tectonics (releases CO 2 ) Plate tectonics – more vigorous then more CO 2 release Climate sensitivity (weathering)

40 CO 2 removal Bicarbonate transport CaCO 3 ppt. CaCO 3 Figs. 8-17 (“regenerates” CO 2 )

41 Short-term Long term (organic) Long term (inorganic/tectonic)

42 Onset of modern plate tectonics “turns this on” “adds” back CO 2 Link with short term C cycle In surface oceans

43 Increase in surface temperature due to increase in solar luminosity Drop in CO 2 by increased weathering at higher temp Decrease greenhouse – increase ppt of carbonates?

44 Bob Berner’s calculations of changes in CO 2 over the Phanerozoic

45 “Hot” houses

46 Bob Berner’s calculations of changes in CO 2 over the Phanerozoic “Hot” houses “Ice” houses

47 Fig. 8-18

48 Effect of humans Pre-industrial –Steady state on decadal to century timescales –Ocean a net source of CO 2 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 CO 2 –Increase sediment and nutrient load to rivers/ocean –Eutrophication, hypoxia, denitrification

49 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.)

50 C org (terr.) 400 C ing 400 CO 2 oxidation rxn. (1) C ing 140 360200 All fluxes are millions of tons of C per year The Ocean 100 (net; approx. 50,000 (r) - 50,100(pp)) Riverine inputs rxn. (1) 200 460 (net) Burial in sediments C org (marine +terr)

51 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

52 N and P Cycles

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54 Global nitrogen reservoirs, fluxes and turnover times. Major reservoirs are underlined, pool sizes and fluxes are given in Tg (10 12 g) N and Tg N yr -1. Turnover times (reservoir divided by largest flux to or from reservoir ) are in parentheses. 80 y -1

55 Atmosphere 120 (NF) 98 (DN) Land 172 (DN) 121 (NF) 27 (RT) Oceans The Pre-Industrial N Cycle (fluxes = Tg N/yr) (1860’s numbers from Galloway et al., 2004)

56 Global sea level Shelf denitrification Area of continental shelves Oceanic fixed-N inventory Oceanic primary productivity Atmospheric CO 2 Greenhouse effectIce volume (+)

57 Fig. 14-13 The iron fertilization hypothesis for the intensification of the biological pump during glaciations. Stimulates N-fixation

58 Atmosphere Terrestrial Ecosystems Aquatic Ecosystems Human Activities Groundwater Effects Surface water Effects Coastal Effects Stratospheric Effects Energy Production PM & Visibility Effects Ozone Effects Agroecosystem Effects NH x Food Production NO x Crop Animal People (Food; Fiber) Soil NO 3 The Nitrogen Cascade NH 3 --Indicates denitrification potential N org Forests & Grassland Soil Ocean Effects N2ON2O GH Effects N2ON2O

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61 Anthro. N fixation = 140 Tg N/yr Retained in soils or denitrified  ≈ 100 yr) - 41 - 8.5 - 9 -3.4 61.9 Tg N/yr 3.4 x (14 to 32) = 50-110 ~80 Tg N/yr missing ?

62 (?)

63 uNO x emissions contribute to OH, which defines the oxidizing capacity of the atmosphere uNO x emissions are responsible for tens of thousands of excess-deaths per year in the United States uO 3 and N 2 O contribute to atmospheric warming uN 2 O emissions contribute to stratospheric O 3 depletion Nr and the Atmosphere

64 Surface water acidification –Tens of thousands of lakes and streams –Biodiversity losses As reductions in SO 2 emissions continue, Nr deposition becomes more important. Nr and Freshwater Ecosystems

65 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

66 There are significant effects of Nr accumulation within each reservoir These effects are linked temporally and biogeochemically in the Nitrogen Cascade

67 Atmosphere Terrestrial Ecosystems Aquatic Ecosystems Human Activities Agroecosystem Effects NH x Food Production Crop Animal People (Food; Fiber) Soil The Nitrogen Cascade N org Galloway et al., 2003a

68 Atmosphere Terrestrial Ecosystems Aquatic Ecosystems Human Activities Groundwater Effects Surface water Effects Coastal Effects PM & Visibility Effects Agroecosystem Effects NH x Food Production Crop Animal People (Food; Fiber) Soil The Nitrogen Cascade NH 3 N org Forests & Grassland Soil Ocean Effects Galloway et al., 2003a

69 Atmosphere Terrestrial Ecosystems Aquatic Ecosystems Human Activities Groundwater Effects Surface water Effects Coastal Effects PM & Visibility Effects Agroecosystem Effects NH x Food Production Crop Animal People (Food; Fiber) Soil NO 3 The Nitrogen Cascade NH 3 N org Forests & Grassland Soil Ocean Effects Galloway et al., 2003a

70 Atmosphere Terrestrial Ecosystems Aquatic Ecosystems Human Activities Groundwater Effects Surface water Effects Coastal Effects Energy Production PM & Visibility Effects Ozone Effects Agroecosystem Effects NH x Food Production NO x Crop Animal People (Food; Fiber) Soil NO 3 The Nitrogen Cascade NH 3 N org Forests & Grassland Soil Ocean Effects Galloway et al., 2003a

71 Atmosphere Terrestrial Ecosystems Aquatic Ecosystems Human Activities Groundwater Effects Surface water Effects Coastal Effects Energy Production PM & Visibility Effects Ozone Effects Agroecosystem Effects NH x Food Production NO x Crop Animal People (Food; Fiber) Soil NO 3 The Nitrogen Cascade NH 3 --Indicates denitrification potential N org Forests & Grassland Soil Ocean Effects

72 Atmosphere Terrestrial Ecosystems Aquatic Ecosystems Human Activities Groundwater Effects Surface water Effects Coastal Effects Stratospheric Effects Energy Production PM & Visibility Effects Ozone Effects Agroecosystem Effects NH x Food Production NO x Crop Animal People (Food; Fiber) Soil NO 3 The Nitrogen Cascade NH 3 --Indicates denitrification potential N org Forests & Grassland Soil Ocean Effects N2ON2O GH Effects N2ON2O

73 Ind. N fix. Population Crop N fix. Total react. N Fossil fuel N F

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76 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.)

77 Sulfur cycle

78 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 Nr and Terrestrial Ecosystems

79 Sulfate Pyrite burial Pyrite uplift and weathering Hydrothermal uptake

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83 H2SH2S SO 2 H2SH2S Sulfate SO 2 DMS

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85 H2SH2S SO 2 DMS Sulfate H2SH2S

86 Ash and debris from volcanic eruptions William Turner, “The fighting Téméraire tugged to her last berth to be broken up” (Tambora) Edvard Munch “The Scream” (possibly inspired by Krakatoa)

87 CloudsTemp. Cloud condensation nuclei DMS Plankton (+) ? (+/-) (+) (neg. feedback; reflectivity) The CLAW Hypothesis

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90 Fig. 14-18 Fig. 14-19


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