Carbon cycle. C on earth Main reservoirs Fluxes between the reservoirs Human impacts Past and present cycles

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1 Carbon cycle C on earth Main reservoirs Fluxes between the reservoirs Human impacts Past and present cycles tools Key element of life Organic chemicals 7 isotopes- 12 and 13 Stable Rest radioactive C14 made from N14 + cosmic rays Relevant time scales of exchange --Carbon can be exchanged between reservoirs in second (fixation) or millennium-accumulation of fossil fuels 1

2 Atmospheric CO2 exchanges rapidly with oceans and terrestrial systems seconds (fixation) Or millenium-accumulation of fossil fuels Controls have changed over time Young earth Anaerobic-methane After atmosphere became oxygenated- Aerobic- CO2 Table Treatise on Geochemistry Fig 11-1 your book Carbon stocks (PgC) Atmosphere Land 2,000 Vegetation 500 Soil 1,500 Ocean 39,000 Surface 700 Deep 38,000 Fossil fuel reserves 10,000 CO2 590 x 10^15 CH4 2 x 10^15 CO x 10^15 SOURCES DIC DOC 1000 Part C Biota 3 Note from S and B NPP on land is ½ of what is measured by sattelites (pg 421) Annual flows (Pg C yr 1 ) Atmosphere-oceans 90 Atmosphere-land 120 Net annual exchanges (Pg C yr 1 ) Fossil fuels 6 Land-use change 2 Atmospheric increase 3 Oceanic uptake 2 Other terrestrial uptake 3 Currently 9 2

3 Figure The contemporary C cycle Now +5 Table 11.1 S and B Importance of fluxes pg 427 1% change in flux of a large pool 15 Pg soils 5 Pg vegetation 7 Pg surface ocean Pool atmosphere (1 S and B) 5 increase per year 2.4 (1.7 S and B) Natural flows of carbon between the land and the atmosphere GPP= GPP = 170 (based on isotopes) Terrestrial biomass Pool-vegetation 610 and soils and detritus 1580 Total 2190 (Fossil fuels 9 Human exhalation 0.6) Surface ocean 1020 Mean RT in air 5 yr Mean RT in surface ocean 5yr 3

4 Pre-industrial Methane Figure Note scale is in Terra grams Tg Sources Table 11.2 Anthropogenic 2x natural Similar seasonal pattern to CO2 due to hydroxl destruction in summer From NASA

5 CO- carbon monoxide Sources and sinks Table11.3 Indirect climate effect- slows destruction of methane Controls troposphere O3- CO + OH makes O3 Figure 3.8b 4/#global_growth 5

6 Oceans Hierarchy of factors Diffusive exchange/solubility pump Revelle factor or buffer factor =10: 1 Function of gas partitioning in the ocean Factor of 10 increase in air only factor of 1 in oceans Varies across the ocean Temperature, salinity, ocean circulation To enter the ocean CO2 gas has to partition into one of the components of Carbonic acid (H 2 CO 3 ) CO 2-3 carbonate, HCO 3- bicarbonate Biological pump Organic C-nutrient linked Carbonate pump Comments from Falkowski et al (2000) Oceans determine atmospheric CO2 CO2 + H2O HCO 3- (bicarbonate) + H+ Balanced by weathering Solubility pump Cold saline waters Biological pumps 6

7 CO 2 storage Ca HCO3- > CaCO3 + CO2 + H2O CO2 + H2O > HCO3- + H+ Alkalinity-operationally defined test of a liquid to determine the solutions ability to neutralize an acid 6CO2 + 6H2O +light > C6H12O6 +6O2 Terrestrial ecosystems Plant uptake and storage in soils main sinks Respiration by plants, microbes Currently thought to be more uptake than respiration 25% of anthropogenic C taken up by plants Factors to consider include nutrient availability, temperature, rainfall 7

8 Plant fixed Respired- NPP the complexity of terrestrial ecosystems make any description of their role in the C cycle an oversimplification. Holmen NPP = GPP R plant (g C m -2 yr -1 ) GPP= CO 2 fixed NPP= CO 2 accumulated CO 2 R p R H R plant ~50% of GPP (relatively constant) NEP = GPP R p R H 8

9 Ecosystem carbon cycle ANPP BNPP Chapin, Matson, Moony 2002 Principles of Terrestrial Ecosystem Ecology Aboveground: Aboveground biomass increment* Fine litterfall* Losses to consumers Volatile and leached organics (VOC, DOC) Belowground: Root biomass increment* Dead roots* Losses to consumers Root exudates & export to symbionts 9

10 Two ways to calculate- Classify biosphere and calculate based on ecosystem measured amounts Use estimates of processes to predict prognositic models Satelllite GPP DO THEY GET IT ALL? Ways to estimate Net primary production (NPP) Field sampling Interannual changes Root allocation not often measured- When it is measured, root growth is often found to contribute significantly to NPP Eddy flux. Measure CO 2 fluxes into canopy during day and out at night using towers, gas samplers at different heights, and sensitive anemometers. Remote sensing Based on absorption and reflectance of light by chlorophyll Chlorophyll absorbs red and blue, reflects green and absorbs little infrared..selective measurements of reflectance give an index of leaf area index (LAI; m 2 m -2 ) There is a good correlation between LAI and production 10

11 Satellite measurements The Integrated Forest Study (Johnson and Lindberg, 1992) Legend: CP=Pinus strobus, Coweeta, NC; DL=Pinus taeda, Duke, NC; GS= Pinus taeda, B.F. Grant Forest, GA; LP= Pinus taeda, Oak Ridge, TN; FS= Pinus eliottii, Bradford Forest, FL; DF=Pseudotsuga menziesii, Thompson, WA; RA=Alnus rubra, Thompson, WA; NS=Picea abies, Nordmoen, Norway; HF=northern hardwood, Huntington Forest, NY; MS=Picea rubens, Howland, ME; WF= Picea rubens, Whiteface, NY; ST= Picea rubens, Clingman s Dome, NC; LV=Pinus contorta/p. jeffreyii, Little Valley, NV. 11

12 TOPOGRAPHY Controls on GPP Chapin et al 2002 Plant uptake of CO2 Factors controlling Stomatal conductance (Figure 5.2) Light Nutrients CO2 Water availability 12

13 Can plants take up more CO2 as we make more? Net exchange is 0 or photosynthesis = respiration Plants close stomata as CO2 increases Influenced by water WUE mmol CO2 fixed mol H O transpired 2 WUE increases as CO2 increases less H2O lost 13

14 Influenced by nutrient availability Nutrient Use Efficiency Nitrogen most limiting Rate of photosynthesis correlated with leaf N Sometimes P concentration related to photosynthesis Leibig s Law of the Minimum Plant growth is controlled not by the total number of resources but by the scarcest Limiting factors Can terrestrial uptake Solve CO 2 excess? 14

15 Figures S and B 5.3-leaf N (and P) important in determining photosynthetic capability NUE WUE Increasing CO2 could mean use less water and need less nutrients GPP influenced by ecosystem age 15

16 Table Treatise on Geochemistry Fig 11-1 your book Carbon stocks (PgC) Atmosphere 780 Land 2,000 Vegetation Soil 1,500 Ocean 39,000 Surface 700 Deep 38,000 Fossil fuel reserves 10,000 Annual flows (Pg C yr 1 ) Atmosphere-oceans 90 Atmosphere-land 120 Net annual exchanges (Pg C yr 1 ) Fossil fuels 6 Land-use change 2 Atmospheric increase 3 Oceanic uptake 2 Other terrestrial uptake 3 Recap Largest pools Small change in these large pools can equate to large change in the atmosphere Small change in the atmosphere concentration of C containing gases large impact on climate, oceans and life Note also large fossil fuel reserve Terrestrial ecosystems large sink for atmospheric CO2 however there are feedbacks between vegetation responses and atmosphere CO2 concentrations Other parameters are important to consider-climate controls, nutrient concentrations - especially N and ecosystem type and age 16

17 Vegetation is linked to precipitation and Precipitation is linked to vegetation! How is soil organic C (that is a large pool) linked to precipitation and NPP? 17

18 Decomposition constant k k litterfall (NPP) detrital mass (forest floor) -2 1 units: g m yr -2 g m yr 1 Olson model (1963) Decomposition NPP (litterfall) What does this tell you about carbon cycling? And future climate? More complicated than this because of soil microbes respiration- 18

19 Substrate quality will influence decomposition Microbes take up as a function C:N They can actually immobilize N and make it not available for plants Changing paradigms regarding competition between microbes and trees C/N ratio Microbes 6:1 to 12:1 Deciduous litter 40:1 to 80:1 Evergreen litter Woody litter 60:1 to 130:1 250:1 to 600:1 SOM 12:1 to 50:1 To understand the strength of the terrestrial carbon sink a lot of things to consider within the framework of anthropogenic induced change CO2 fertilization Nitrogen fertilization Ozone and sulfur effect Climate change-increase storage? increase processing? Higher temperatures/more rain more microbial processing N limitation Soil C availability 19

20 Analyses of change over time Ice cores data used to understand the change in concentrations Ice core limitations Midieval optimum /Little ice age Law Dome Ice Core Treatise on Geochemistry Long term Carbon cycle Trying to understand the past carbon cycle Antartica Little ice age Figure Medieval climate optimum

21 Understanding Quaternary changes Abrupt warming and then cooling Chpt 8.09 Figure 7 Vostok ice core, Antartica 3km depth CO2 and CH4 and H isotopes all show same change Dust and Na increase due to glaciation yrs data Falkowski Can we distinguish between natural and anthropogenic perturbations in climate? What is the Earth s sensitivity to climate? 21

22 True statement We have driven the Earth from the tightly bounded domain of glacial-interglacial periods. Comments from Falkowski et al (2000) During glacial periods the atmosphere acts to transfer C between atmosphere and oceans. Remarkable consistency of upper and lower CO2 suggests fine tuned controls and feedbacks Gradual transition into glacial periods versus steep from glacial to interglacial 22

23 Regulators DIC in ocean 50* air-ocean regulates over millennia needs minerals to sequester Efficiency of solubility pump-spatially variable (impacts of changes in climate Surface ocean lower than deep ocean Climate warming ocean stratification Biological pump-phytoplankton keep the atmosphere ppmv lower Carbonate pump- release C Terrestrial C system Regulators Currently not saturated CO2 uptake biochemically, nutrient, water limited Warmer higher respiration-less of a terrestrial sink Land use change 23

24 EJc Pg Cd Reserves Oil conventional 1,2,3,4,5,6 5,908 6, Oil unconventional 1,2 6,624 8, Natural gas conventional 1,2,3,4,5,6 5,058 6, Natural gas unconventional 1,2 8,102 8, Coal 1,2,4,6 28,825 41, ,094 Resources Oil conventional 1,2,3,5, a 6,490 14, Oil unconventional 1,2, a 14,860 15, Natural gas conventional 1,2,3,5, b 9,355 12, Natural gas unconventional 1,2, b 10,787 11, Coal 1,2 100, ,059 2,605 3,177 Additional occurrences Oil unconventional 1,2 61,008 85,004 1,145 1,596 Natural gas unconventional 1,2 15,979 17, Coal 1,2 120, ,280 3,122 3,411 Table 1b Comments on the great biogeochemical experiment Long term carbon sequestration by ecosystems unlikely Ocean response highly uncertain Human carbon sequestration solution? Planetary response-weathering-gaia 24

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