CHAPTER 6: GEOCHEMICAL CYCLES

Transkript

1 CHAPTER 6: GEOCHEMICAL CYCLES THE EARTH: ASSEMBLAGE OF ATOMS OF THE 92 NATURAL ELEMENTS Most abundant elements: oxygen (in solid earth!), iron (core), silicon (mantle), hydrogen (oceans), nitrogen, carbon, sulfur The elemental composition of the Earth has remained essentially unchanged over its 4.5 Gyr history Extraterrestrial inputs (e.g., from meteorites, cometary material) have been relatively unimportant Escape to space has been restricted by gravity Biogeochemical cycling of these elements between the different reservoirs of the Earth system determines the composition of the Earth s atmosphere and oceans, and the evolution of life

2 BIOGEOCHEMICAL CYCLING OF ELEMENTS: examples of major processes Physical exchange, redox chemistry, biogeochemistry are involved Surface reservoirs

3 EVOLUTION OF O 2 AND O 3 IN EARTH S ATMOSPHERE

4 NOAA Greenhouse Gas records

5 Nitrogen: Nitrogen is a major component of the atmosphere, but an essential nutrient in short supply to living organisms. Why is "fixed" nitrogen in short supply? Why does it stay in the atmosphere at all? OXIDATION STATES OF NITROGEN N has 5 electrons in valence shell a9 oxidation states from 3 to +5 Increasing oxidation number (oxidation reactions) NH 3 Ammonia NH 4 + N 2 N 2 O Nitrous oxide NO Nitric oxide HONO Nitrous acid NO 2 - NO 2 Nitrogen dioxide HNO 3 Nitric acid NO 3 - Ammonium Nitrite Nitrate R 1 N(R 2 )R 3 Organic N free radical free radical Decreasing oxidation number (reduction reactions)

6 THE NITROGEN CYCLE: MAJOR PROCESSES ATMOSPHERE Kunstgjødsel N 2 combustion lightning NO free radical oxidation BIOSPHERE burial orgn assimilation (bacteria or host plants biofixation (bacteria) decay (bacteria) denitrification (bacteria, anaerobic) HNO 3 NH 3 /NH 4 + NO 3 - nitrification (bacteria, aerobic) deposition weathering LITHOSPHERE "fixed" or "odd" N is less stable globally N 2

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8 Box 6.2, Figure 1 Anthropogenic reactive nitrogen (Nr) creation rates (in TgN yr 1) from fossil fuel burning (orange line), cultivation-induced biological nitrogen fixation (blue line), Haber Bosch process (green line) and total creation (red line). Source: Galloway et al. (2003), Galloway et al. (2008). Note that updates are given in Table 6.9. The only one with significant changes in the more recent literature is cultivation-induced BNF) which Herridge et al. (2008) estimated to be 60 TgN yr 1. The data are only reported since 1850, as no published estimate is available since IPCC WGI, 2013

9 Effekter av økt utslipp av reaktivt nitrogen Stratosfæren: Ozontap (N 2 O) Vann/sjø: Eutrofiering Troposfæren: Ozon Oksidasjonskapasitet Partikkeldannelse

10 Økning i N 2 O konsentrasjonen de siste 2000 år. Fra 270 ppbv til 325 ppb (+20%)

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12 FAST OXYGEN CYCLE: ATMOSPHERE-BIOSPHERE Source of O 2 : photosynthesis nco 2 + nh 2 O g (CH 2 O) n + no 2 Sink: respiration/decay (CH 2 O) n + no 2 g nco 2 + nh 2 O CO 2 O 2 lifetime: 5000 years Photosynthesis less respiration O 2 orgc litter orgc decay

13 however, abundance of organic carbon in biosphere/soil/ocean reservoirs is too small to control atmospheric O 2 levels Atmosfære Atmosfære C << O Dette kontrollerer ikke O 2 nivået i atmosfæren!

14 SLOW OXYGEN CYCLE: ATMOSPHERE-LITHOSPHERE O 2 : 1.2x10 6 Pg O O 2 lifetime: 3 million years Photosynthesis decay O 2 CO 2 Fe 2 O runoff 3 H 2 SO 4 O 2 CO 2 weathering FeS 2 orgc OCEAN orgc CONTINENT SEDIMENTS burial orgc CO 2 microbes FeS 2 Compression subduction Uplift orgc: 1x10 7 Pg C FeS 2 : 5x10 6 Pg S

15 Antarctic Ice Core Data CO 2 varies over geologic time, within the range ppm for the last 420,000 years. The variations correlate with climate: cold low CO 2. Is CO 2 driving climate or vice versa? The heavier temperature lines 160,000 BP to present reflect more data points, not necessarily greater variability. Source: Climate and Atmospheric History of the past 420,000 years from the Vostok Ice Core, Antarctica, by Petit J.R., Jouzel J., Raynaud D., Barkov N.I., Barnola J.M., Basile I., Bender M., Chappellaz J., Davis J. Delaygue G., Delmotte M. Kotlyakov V.M., Legrand M., Lipenkov V.M., Lorius C., Pépin L., Ritz C., Saltzman E., Stievenard M., Nature, 3 June 1999.

16 Det Global karbonbudsjettet 1 Pg = g = 1000 mill tonn

17 Det Global karbonbudsjettet 1 Pg = g = 1000 mill tonn Fotosyntes e Respirasjo n/nedbrytni ng

18 Det Global karbonbudsjettet

19 Det Global karbonbudsjettet

20 Det Global karbonbudsjettet

21 Det Global karbonbudsjettet Stor utveksling mellom atmosfære og planter/hav Levetid CO 2 : 820(PgC)/( PgC/år) = 4 år Mye karbon i dyphavet Veldig tregt tap av karbon til olje/kull/gass Kilde:

22 Jacob (1999): FF: 6 Pg(C)/yr Avskoging: 1.6 Pg(C)/yr Økning atm: 4 Pg(C)/yr Opptak (hav/land): 3.6 Pg(C)/yr IPCC (2013): FF: 9.5 Pg(C)/yr Avskoging: 1.0 Pg(C)/yr Økning atm: 4 Pg(C)/yr Opptak hav: 2.5 Pg(C)/yr Opptak land: 2 Pg(C)/yr IPCC, 2013

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24 Årlig observert økning i CO2 (IPCC, Fig 6.12)

25 Forskjell NH/SH skyldes mer utslipp fra fossile kilder i nord. IPCC, 2013

26 Photosynthesis: Carbon Cycle on Land CO 2 + H 2 O + light => "H 2 CO" + O 2 Respiration: "H 2 CO" + O 2 => CO 2 + H 2 O + energy Very little organic matter is stored, on average. Dissolution/evasion Carbon Cycle in the ocean CO 2(g) + H 2 O + CO 3(aq) = 2 HCO 3

27 Karbonkjemi i havet M=mol/liter (Molar) CO 2 løses i vannet og danner CO 2 H 2 O Likevekt ved Henrys lov K H = [CO 2 H 2 O]/P CO2 = M/atm CO 2 H 2 O dissosierer og danner HCO - 3 og H + K 1 = [HCO 3- ][H + ]/[CO 2 H 2 O] = M HCO - 3 dissosierer og danner CO 2-3 og H + K 2 = [CO 2-3 ][H + ]/[HCO - 3 ] = M ph = -log [H + ] Lav ph [H + ] høy [H + ] høy R5 og R4 forskjøvet mot venstre ph i havet (pre-industrielt): 8.2 Ønsker å finne F(K i, [H + ])

28 Ønsker å finne F(K i, [H + ]) = 0.03 Betyr dette at 97% av ekstra tilført CO 2 blir tatt opp i havet?

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30 Nei, mer CO 2 betyr mer H + slik at F øker Buffereffekten av HCO 3 - og CO 3 2- NB! Buffereffekten hindrer ikke at [H + ] øker, men demper økningen betydelig Ved en ekstra tilførsel av CO 2 til atmosfæren (dn), hvor mye blir værende?

31 Lang utregning. (se side 102 i boka) = 0.28 Betyr dette at 72% av ekstra tilført CO 2 blir tatt opp i havet? Ja, men ikke umiddelbart! - V OC er volumet av hele havet, og blandingen ned i dyphavet er treg. - Høyere temperatur ved overflaten (?) varmere vann på overflaten tregere blanding Dersom vi bare tar med overflatelaget blir f=0.94

32 Hvordan tas resten av CO2 opp? IPCC, 2013 CO 2 (g) + CaCO 3 2HCO Ca 2+ f=7%

33 IPCC, 2013

34 Hvordan blir CO 2 fjernet på enda lengre tidsskalaer? Forvitring av mineraler som består av kalsiumsilikat (CaSiO 3 )

35 CO 2 opptak i havet til nå IPCC, 2013

36 IPCC, 2013

37 Notice: atmospheric increase is ~50% of fossil fuel emissions significant interannual variability Arrows indicate El Nino events

38 EVIDENCE FOR LAND UPTAKE OF CO 2 FROM TRENDS IN O 2,

39 Dagens CO 2 budsjett. IPCC, 2013

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41 CO2 utslipp per person.

42 CYCLING OF CARBON WITH TERRESTRIAL BIOSPHERE Inventories in PgC Flows in PgC yr -1 Relatively small reservoirs a Short time scales a net uptake from reforestation is transitory...unless resources are managed to preserve organic matter

43 Biogeokjemiske tilbakekoblinger T øker økt/redusert plantevekst økt/red CO 2 opptak negativ/positiv tilbakekobling CO 2 øker økt plantevekst økt CO 2 opptak negative tilbakekobling (såkalt non-climate feedback)

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46 IPCC, 2013

47 Uendret klima, høyere CO2 Mer CO 2 i atmosfæren høyere opptak i hav og på land Varmere klima, uendret CO2 Høyere temperatur høyere/lavere opptak i hav og på land

48 Varmekraftverk basert biobrensel og CCS: En mulighet for negative CO 2 utslipp?

49 ATMOSPHERE CO 2 (g) UPTAKE OF CO 2 BY THE OCEANS OCEAN K H = 3x10-2 M atm -1 CO 2. H 2 O K 1 = 9x10-7 M CO 2. H 2 O HCO H + K 2 = 7x10-10 M HCO 3 - CO H + CO 2. H 2 O HCO 3 - CO 3 2- Net uptake: CO 2 (g) + CO H 2 O 2HCO 3 -

50 EQUILIBRIUM PARTITIONING OF CO 2 BETWEEN ATMOSPHERE AND GLOBAL OCEAN Equilibrium for present-day ocean: N ( g) ( ) ( ) F CO2 N g CO2 N aq CO varies roughly as [H + ] only 3% of total inorganic carbon is currently in the atmosphere But CO 2 (g) k [H + ] k F k positive feedback to increasing CO 2 Pose problem differently: how does a CO 2 addition dn partition between the atmosphere and ocean at equilibrium? f dnco2( g) dn ( g) dn ( aq) CO2 CO varies roughly as [H + ] 2 28% of added CO 2 remains in atmosphere!

51 FURTHER LIMITATION OF CO 2 UPTAKE: SLOW OCEAN TURNOVER (~ 200 years) Inventories in m 3 water Flows in m 3 yr -1 Uptake by oceanic mixed layer only (V OC = 3.6x10 16 m 3 ) would give f = 0.94 (94% of added CO 2 remains in atmosphere)