Dynamic interactions of geochemical cycles

Transcription

1 The Carbon Cycle Marine Perspectives 1

2 Dynamic interactions of geochemical cycles Oceanography (study of the oceans), and Chemical Oceanography (chemistry of the oceans based on the distribution and dynamics of elements, isotopes, atoms and molecules) are fundamentally interdisciplinary sciences that deal with dynamic interactions between atmosphere, lithosphere and hydrosphere 2

3 The broadest we can get: Global warming 3

4 Spektrale Energieflußdichten für solare und terrestrische Strahlung 4

5 Die nicht absorbierende Atmosphäre Bilanz der reinen (N 2, O 2, Ar) Atmosphäre: Etwa 6% atmosphärische Rückstreuung, etwa 10% Reflexion an Oberfläche Land und Ozean Mittlere Einstrahlung 288 W/m 2 Schwarzkörperstrahlung gegeben durch Stefan-Bolzmann-Gesetz: R = σ T 4 a σ = Stefan Bolzmann Konstante (5.67 x 10-8 J m -2 K -4 s -1 ) T a = abs. Temperatur T a (288W/m^2) = - 6 C Real : T av = + 15 C 5

6 Das solare Spektrum Einfluß der Atmosphäre auf die Einstrahlungsbilanz, mit Wolkenalbedo, Wasserdampf, CO 2 etc: Einfallende Strahlung 342 W/m 2, etwa 70% durch die Atmosphäre und am Boden absorbiert, i.e. 240 W/m 2 => -18 C 6

7 Überblick 7

8 Absorption im IR- Bereich Breite Absorption durch Wasserdampf im IR- Bereich,zusätzliche Absorptionsbanden von CO 2 Ozon, Methan und N 2 O FCKW absorbieren stark genau in den optischen Fenstern der Atmosphäre 8

9 Überblick 9

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11 History of the science of the greenhouse effect 1827: Jean Baptiste t Fourier recognizes the effect of IR absorbing gases and points out the similarity to a greenhouse 1860: John Tyndall measures IR absorption of CO 2 and water vapor, he suggests that the cause of the ice ages might be a decrease in atmospheric CO : Svante Arrhenius calculates the effect of rising greenhouse gas concentrations on temperature; estimates 5-6 C increase for a CO 2 doubling 1940: G.S. Callendar does a first calculation on temperature increase due to the burning of fossil fuels 1957: Roger Revelle and Hans Suess;.. In the build-up of carbon dioxide in the ocean, human beings are carrying out a large-scale geophysical experiment. 11

12 Atm. CO2 (ppm) 12

13 The Carbon Cycle Transfer of carbon between chemical reservoirs Living things (biosphere) Sediments (geosphere) Organic matter/kerogen Oil, Gas, Clathrates Carbonate/Limestone CaCO 3 Oceans (hydrosphere) HCO 3 Atmosphere (atmosphere) CO 2 13

14 Looking at carbon cycles Atmospheric increase from pre-industrial 280 ppm in 1800 to 380 ppm today This is only % of the expectation ti based on release figures from fossil fuel burning and cement production (244 +/- 20 x g from 1800 to 1994) About 116 +/- 19 x g taken up by the ocean from 1850 to 1994 (Sabine et al., 2004) So what is the role of the ocean and how does its carbon system work? 14

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17 The fast exchanging carbon reservoirs After Siegenthaler and Sarmiento, Entire deep ocean:

18 Getting conceptual: a box model view 18

19 The Carbon Cycle - Reservoirs Reservoirs in g Atmosphere 760 Ocean 38,400 (as DIC) Land biota 600 Marine biota 3 Soil organic matter 1,600 Sedimentary rocks 78,000,000 Fossil fuels 5,000 Gas hydrate deposits 3,000 19

20 The Geological Carbon Cycle Cycling of carbon between rocks and minerals, seawater, and the atmosphere. 20

21 The Geological Carbon Cycle Fluxes in gc/yr 21

22 Chemical Weathering Dissolution of carbonate CO 2 + H 2 O <=> H 2 CO 3 <=> H + + HCO 3 CaCO <=> 2+ 3 H HCO 3 Ca + 2HCO

23 Carbon Cycle - Feedbacks 23

24 Long-term Trends Atmospheric CO 2 controlled by rates of weathering, plate tectonic t cycling/ seafloor spreading Weathering rate based on total land area => mountain building! Ultimately, the geochemical carbon cycle regulates the long term atmospheric concentration of CO 2 24

25 Long-term Trends 25

26 So Back to the millenium timescale 26

27 Controls on the carbonate system The shortest description of the carbonate system EVER: CO 2gas + H 2 O = H 2 CO 3 = H + + HCO - 3 Attention : pco 2(T) ~ pco 2(To) x ( (T-To)) HCO - =H + +CO ph-dependent carbonate speciation CO 2 +H 2 O = C(H 2 O) + O 2 Organic matter formation and decomposition Ca HCO 3- = CaCO 3 + CO 2aq Carbonate formation Carbonate formation means more acid and depletion of CO 2-3 Organic matter formation means less acid and increase of CO 2-3 Remineralization of organic matter means more acid and depletion of CO

28 Air-Sea Exchange 28

29 decreasing 29

30 warming 0ºC 24ºC 63 mmol/kg CO 2(aq) 29 mmol/kg CO 2(aq) At equilibrium with atmosphere At 24 C, should only be 29 mmol/kg CO 2(aq) Supersaturated by 34 mmol/kg Warming is the only process that t has affected this water mass. For a closed system, warming alone will lead to supersaturation. Cooling will have the opposite effect. 30

31 Gas Exchange Flux out Fluxes are equal at equilibrium. At disequilibrium, net transport occurs to alleviate the imbalance. Flux in Processes that cause imbalance: production/consumption of a gas in water, production/consumption of a gas in atmosphere, temperature changes 31

32 Gas Exchange Fick s 1st Law of Diffusion F = -D(dC/dz) F = flux (mass/area time) D = molec. diffusion coeff. (area/time) dc/dz = con cgradientc dc/dz = (C g -C l )/z Stagnant Boundary Layer Model F = -(D/z)(C g -C l ) K H *p air = F = flux (mass/area time) D = molec. diffusion coeff. (area/time) z = thickness of film C l = con c of gas in mixed layer C g = con c of gas in water at top of film 32

33 biogeochemical cycles Dissolved constituents t (C, N, P, Si ) are converted into particulate constituents along the way. Satellite Image - Reflectance Coccolithophorids Photosynthesis (forward) Respiration (reverse) CO 2 + H 2 0 CH O + O + 2 Ca + 2 HCO 3 CaCO 3 + CO 2 + H 2 O 2 Precipitation (forward) Dissolution (reverse) 33 2

34 Ocean circulation 34

35 biogeochemical cycles Through the particle conspiracy, horizontal and vertical segregation of dissolved chemicals occurs. (see Surface Ocean Deep Ocean The Great Particle Conspiracy 35

36 The outcome of the conveyer belt 36

37 Unit for the saturation state of seawater vor calcite Carbonate saturation With: 37

38 Ocean circulation 38

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42 The biological and the physical pump Chisholm ( 2000) Nature, 407:

43 Processes conceptualized in the context of biogeochemical cycles Connectivity of air sea land through tectonics, erosion/weathering, sedimentation Burial of these two materials in sediments has different effects on the partial pressure of CO 2 in the atmosphere! Why? 43

44 ASE fluxes Global annual mean CO 2 -fluxes as a result of an integrated compilation (from Takahashi et al., DSR II, 2002). 44

45 Atm. CO2 (ppm) 45

46 Die anthropogene Störung des Kohlenstoffkreislaufs 1.9 Atmosphere (590) 1.7 (610) (74) (74) (900) (1.560) (90) Terrestrische Biosphäre (37.100) Ozean Fossil Fuels

47 Die anthropogene Störung des Kohlenstoffkreislaufs 2070? ERREST TRIAL IOSPHE ERE ATMOSPHERE Physical Pump Biological Pump T B OCEAN 47

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49 σ θ = 26 surface is near the surface, shallower in the Atlantic WHY σ θ = 27.3 is approximately at 900 m water depth (intermediate water masses) Fig. 4. Maps of anthropogenic CO 2 on the (A) 26.0 and (B) 27.3 potential density surfaces. Bold lines at the edge of the colored region indicate areas where the density surface outcrops. The highest values are generally observed closest to the outcrop and decrease toward the equator. (Sabine et al., 2004) 49

50 CARBOOCEAN Marine inventory of anthropogenic CO 2 Invasion of anthropogenic CO 2 into the oceans (source: Sabine et al., Science, 2004) 50

51 Fig. 1. Column inventory of anthropogenic CO 2 in the ocean (mol / m2). High inventories are associated with deep water formation in the North Atlantic and intermediate and mode water formation between 30 and 50 S. Total inventory of shaded regions is 106 +/-17 Pg C (from Sabine et al, 2004). 51

52 Feedbacks pco 2 -T surface -CO 2 solubility f (T) pco 2 -T surface - Ocean circulation pco 2 => weathering (slow) Some more sophisticated controls 52

53 Advanced studies: Effect of changing atmospheric pco 2 on the rain rate Riebesell et al., Nature 407, , 2000 Atmospheric (and thus surface ocean) pco 2 is expected to increase by a factor of 3 with respect to preindustrial levels by the end of the 21th century Rising pco 2 -levels in the surface ocean are already known to affect coral reef calcification (actually, T rather than pco 2 ). Ocean carbonate system however more controlled by calcifying phytoplankton (80% of calcification, most dominant coccolithophores) Test of effect by exposing widespread coccolithophores to various pco 2 levels and observe impact on calcification 53

54 Advanced studies: Effect of changing atmospheric pco 2 on the rain rate Riebesell et al., Nature 407, ,

55 The Carbon Cycle Marine Perspectives 55