Soil

SoilPaleoclimate & Methane: 

Soil Paleoclimate & Methane Gerrit Lohmann Carbon Course 26. January 2006 @PEP, University of Bremen, Germany

Paleoclimate: 

Paleoclimate

Anomalien und Spektren: 

Anomalien und Spektren

Slide5: 

Northern Hemisphere Summer Boreal Summer Annual Cycle

Slide6: 

Northern Hemisphere Summer Boreal Summer Annual Cycle We have summer They have winter

Slide7: 

Annual Cycle Fixed axis of Earth rotation

Slide10: 

Precession & Eccentricity Present Orbital Configuration: Winter Solstice close to the position of Perihelion

Slide12: 

Obliquity caused by gravitational interactions with other planets

Obliquity: 

Obliquity

Slide14: 

Effect on climate: Monsoon

Effect on climate: 

Effect on climate Southen margin of the Sahara Desert Congo Air Boundary (CAB) Rough locations of the Intertropical Convergence Zone (ITCZ)

Slide18: 

Diatoms: A key player for the marine biosphere Increase in export production Dust affects the radiation balance

Methane: Sources & Sinks: 

Methane: Sources & Sinks

Methane: Sources: 

Methane: Sources Wiederkäuer

Methane Hydrate: 

Methane Hydrate Methane hydrate consists of a cage of water molecules trapping a methane molecule within. This forms large crystals of hydrate in cold and heavily pressurized situations mainly on the continental slope in the oceans.

Slide25: 

Oxygen isotope values (left column) and carbon isotopic values of the deep sea for the Cenozoic, after Zachos, et al.2001 Note that more negative d18O values mean that water temperature was higher, or the polar ice sheets were smaller, or both.

Globale Klimaschwankungen: 

Globale Klimaschwankungen 450 000 Jahre 4 Milliarden Jahre Menschen seit 2 Millionen Jahren

Carbon Cycle: 

Carbon Cycle Marine terrestrial

Slide30: 

Organic Carbon cycle oxidation

Slide31: 

Photosynthesis -> low PO4, organic matter with 12-C, residual water high 13-C

Slide32: 

OCEANIC PHOTOSYNTHESIS – can utilize either CO2(g) or HCO3- +0.9‰ equil. +7-8‰ equil. C isotopes inorganic C (carbonates): typically -1‰ to +1‰ PDB organic C: typically -5‰ to -15‰ PDB d13C of marine organisms varies because: [CO2(aq)] small in warm tropical waters, fractionation low pH varies, and each inorganic DIC species has different fractionation temperature low at poles, fractionation increases surface-to-deep gradients (upwelling zones have lower d13C(sw))

Slide33: 

Atlantic Ocean

Slide34: 

Pacific Ocean waters out of contact with the surface ocean for a long time

Slide35: 

Circulation and productivity changes Changes in 13-C Present day Glacial

Slide36: 

13-C: climate changes

Köppen/Geiger - Klassifikation: 

Köppen/Geiger - Klassifikation

Stable Isotope Meaurements:1 millimeter in a Kilometer: 

12C 98.89% 14N 99.7% 13C 1.11% 15N 0.3% Isotopic Composition () 13C (‰) = [13C/12C sample/ 13C/12C standard -1] x 1000 Atmos. CO2 13C = -8 ‰ Grass 13C = -12.5 ‰ Leaves 13C = -26 ‰ Stable Isotope Meaurements: 1 millimeter in a Kilometer

Laws of Isotopes —It’s Physics and Chemistry: 

Laws of Isotopes — It’s Physics and Chemistry First Law: The lighter isotope reacts faster and requires less energy of activation. Second Law: The heavier isotopes make the strongest bonds. Zeroth Law: Beware of changes less than 1 ‰!

Slide42: 

green = reservoir size (1015g, Gigatons) red = fluxes (Gt/yr) Reservoirs and fluxes from Schlesinger, 1991; d13C from Heimann & Maier-Reimer, 1996 The Carbon Cycle *NOTE: d13C always reported in PDB

Slide43: 

green = reservoir size (1015g, Gigatons) red = fluxes (Gt/yr) blue = C isotopic value Reservoirs and fluxes from Schlesinger, 1991; d13C from Heimann & Maier-Reimer, 1996 The Carbon Cycle *NOTE: d13C always reported in PDB

Terrestrial Biosphere: 

Terrestrial Biosphere The main fractionating process is due to the photo-synthetic fixation of carbon with organic matter being depleted in the heavy isotope (isotopically light). The simplified reaction for photosynthesis is:  6CO2 + 6H2O -> C6H12O6 + 6O2

Slide45: 

C3 Pathway enzyme-mediated (RUBISCO) -RUBISCO fixes 1 O2 for every 5 CO2 “Calvin” cycle 90% of all plants 20-30‰ fractionation TERRESTRIAL PHOTOSYNTHESIS - theoretical calculations predict a 4.4‰ kinetic fractionation for CO2(g) moving from air through stomata to site of photosynthesis d13C and Photosynthesis

Slide46: 

C4 Pathway desert plants, some tropical species enzyme-mediated (PEP) “Hatch-Slack” cycle 10% of all plants 13‰ fractionation NOTE: C4 plants still execute “Calvin” cycle, but CO2 grabbing and actual carbon fixation happening in different cells

C3: Stowaway: 

C3: Stowaway 1) Rubisco will sometimes recognize oxygen as a substrate instead of CO2 The plant has made extra work for itself in creating phosphoglycolate, a nearly useless compound. This reaction directly competes with the regular reaction, mostly in warm climates 2) Plants living in arid climates have to close the pores in their leaves when it is particulalry dry, or they will wither. Temperature oxygen instead of carbon dioxide

Solution: 

Solution Plants living in the above mentioned difficult conditions have discovered a way to make the carbon dioxide concentration very high in the immediate environment of Rubisco, so that the oxygenase reaction does not get a chance to happen. NOTE: C4 plants still execute “Calvin” cycle, but CO2 grabbing and actual carbon fixation happening in different cells

Slide49: 

C4 plants photorespiration is lower than in C3 plants (respiration during photosynthesis). C4 plants: maize, sugarcane, some tropical grasses C3 plants: all trees, temperate grasses Isotopic fractionation of 13C during photosynthesis differs for C3 and C4 plants: In C4 plants an initial step preceeds the Calvin cycle (-> 4 steps =C4) fractionation: C3: -15 to -23 o/oo versus C4: -2 to -8 o/oo

Isotopic Fractionation 1: 

Isotopic Fractionation 1 13Csample = ((13C/12Csample)/(13C/12Cstd) – 1) * 1000 13C/12Cstd = 0.0112372 per definition average CO2 in atmosphere: 13Catm = -8.0 o/oo (permil) carbon fixed by C3 plants: 13CC3 ~ 13Catm + (C3) = -8 o/oo-20 o/oo = -28 o/oo carbon fixed by C4 plants: 13CC4 ~ 13Catm + (C4) = -8 o/oo-5 o/oo = -13 o/oo Process behind: The molecule enriched in 13C is heavier and is therefore discriminated during exchange processes (heavier~slower in its movements)

Biological Laws of Isotopes: 

Biological Laws of Isotopes Key reactions (e.g. Photosynthesis) label the “bulk” of the organism. You are what you eat--with some modification. Every biochemical reaction imparts an isotopic label on the products and reactants.

Development of the Proxy: 

Development of the Proxy Ratite=Laufvogel

Slide53: 

Allison, C.E. et al., “TRENDS”, DOE, 2003. d13C of atmospheric CO2 What feature do they share and why? Why do they differ? Atmospheric biogeochemists use a global network of flask collections to track CO2 from sources to sinks ex: most emissions are in N.H., but N-S gradient is small – therefore N.H. must be taking up large amount of emissions

Atmospheric CO2 measurements: 

NOAA-CMDL ~ 100 sites Long-term increase in CO2 burden Seasonal cycle N-S gradient Atmospheric CO2 measurements

Slide55: 

d13C CO2 d13C and [CO2] for last 200 years – ice core bubbles in Siple Station, Antarctica Suess Effect progressive depletion of CO2 resulting from burning of isotopically light fossil fuels ~1.5‰ over last century

Isotopic fractionation : 

Isotopic fractionation Determine the isotope ratio of respired CO2 from the soil or from ecosystems. CO2 samples during a period when the CO2 concentration is changing over time. At the night when photosynthesis has ceased, the CO2 concentration above the soil or the plant canopy increases as the ecosystem respires. If the CO2 concentration is near the atmospheric value of 365 ppm, then the sample mostly contains atmospheric CO2, and d13C is near -8‰.  When the CO2 concentration rises above the atmospheric concentration, it contains a larger proportion of respired CO2, which has a more negative carbon isotope ratio.

Isotopic fractionation : 

Isotopic fractionation Fractionation is species specific and 13C is therefore used to identify thoses plant species involved in exchange processes Consider a two reservoir system C2 = C0 + C1 C0: background CO2; C1: respiration flux of reservoir (plants, soil) to atmosphere C2: resulting CO2 after exchange process d13C2 * C2 = d13C0 * C0 + d13C1 * C1 d13C2 = d13C0 * C0/C2 + d13C1 * C1/C2 d13C2 = d13C0 * C0/C2 + d13C1 * (C2-C0)/C2 d13C2 = (d13C0 - d13C1) * C0/C2 + d13C1 C0 C1

Isotopic fractionation : 

Isotopic fractionation Fractionation is species specific and 13C is therefore used to identify thoses plant species involved in exchange processes Consider a two reservoir system C2 = C0 + C1 C0: background CO2; C1: respiration flux of reservoir (plants, soil) to atmosphere C2: resulting CO2 after exchange process d13C2 * C2 = d13C0 * C0 + d13C1 * C1 d13C2 = d13C0 * C0/C2 + d13C1 * C1/C2 d13C2 = d13C0 * C0/C2 + d13C1 * (C2-C0)/C2 d13C2 = (d13C0 - d13C1) * C0/C2 + d13C1 C0 C1

Isotopic fractionation : 

Isotopic fractionation Fractionation is species specific and 13C is therefore used to identify thoses plant species involved in exchange processes Consider a two reservoir system C2 = C0 + C1 C0: background CO2; C1: respiration flux of reservoir (plants, soil) to atmosphere C2: resulting CO2 after exchange process d13C2 * C2 = d13C0 * C0 + d13C1 * C1 d13C2 = C0 (d13C0 – d13C1) * 1/C2 + d13C1 y = m * x + b linear equation between new d13C2 and 1/C2, with d13C1 as y-axis intercept, called KEELING PLOT

Keeling plot (C.D.Keeling,1958): 

Keeling plot (C.D.Keeling,1958) Pataki et al 2003 Two important limitations: 2 reservoir system Fast process

Keeling plot 2: 

Keeling plot 2 Seasonal cycle in atm 13C, CO2 has its origin in the variability of the terrestrial biosphere (d13C0 ~ -25 o/oo)

Atmospheric CO2 Budget: 

Atmospheric CO2 Budget How do we partition the carbon sink between land and ocean? Land and Ocean Sinks Atmospheric Increase

Slide63: 

NOAA/CMDL CU-INSTAAR

13C budget equations forland/ocean partitioning: 

13C budget equations for land/ocean partitioning Tans et al. 1993 Battle et al. 2000 CO2 mass balance 13CO2 mass balance 20 ‰ 2 ‰ -28 ‰ -28 ‰ Disequilibrium (Giso) term is largely model-based