![Page 1: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/1.jpg)
Carbon isotopes in the biosphere 10/23/12and geologic record
Lecture outline:1) the carbon cycle
and δ13C
2) C fractionationin the terrestrialbiosphere
3) C isotopes in the ocean
4) C isotopes in theatmosphere
Photo of a C3 leaf cross-section
![Page 2: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/2.jpg)
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: δ13C always reported in PDB
![Page 3: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/3.jpg)
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
δ13C and Photosynthesis
![Page 4: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/4.jpg)
C4 Pathway-desert plants, some
tropical species-enzyme-mediated (PEP)-“Hatch-Slack” cycle-10% of all plants-13‰ fractionation(beggars can’t bechoosers…)
NOTE: C4 plants still execute “Calvin”cycle, but CO2 grabbing and actualcarbon fixation happening in different cells
![Page 5: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/5.jpg)
![Page 6: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/6.jpg)
Schoeninger and DeNiro, 1984
δ13C of living organisms: you are what you eat,plus a little bit
Why are higher trophicorganisms progressivelyhigher in δ13C?
![Page 7: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/7.jpg)
δ13C and CO2 in soils
Why are soil CO2 andδ13C correlated?
![Page 8: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/8.jpg)
Allison, C.E. et al., “TRENDS”, DOE, 2003.
δ13C of atmospheric CO2
What feature do they share and why?
Why do they differ?
Atmospheric biogeochemists use aglobal network of flask collectionsto track CO2 from sources to sinks
ex: most emissions are in N.H., butN-S gradient is small – thereforeN.H. must be taking up large amountof emissions
![Page 9: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/9.jpg)
δ13C
CO2
δ13C and [CO2] for last 200 years – ice core bubbles in SipleStation, Antarctica
Suess Effectprogressive depletion of CO2
resulting from burning of isotopically light fossil fuels~1.5‰ over last century
![Page 10: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/10.jpg)
OCEANIC PHOTOSYNTHESIS – can utilize either CO2(g) or HCO3-
+0.9‰ equil. +7-8‰ equil.
When thinking about how C isotopes move through the ocean, we mustdifferentiate between inorganic C (carbonates): typically -1‰ to +1‰ PDBand organic C: typically -5‰ to -15‰ PDB
However, the ocean, unlike the atmosphere, is NOT well-mixed.δ13C of marine organisms varies because:• [CO2(aq)] small in warm tropical waters, fractionation low• pH varies, and each inorganic DIC species has different • temperature low at poles, fractionation increases• surface-to-deep gradients (upwelling zones have lower δ13C(sw))
![Page 11: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/11.jpg)
δ13C of Dissolved Inorganic Carbon (DIC) in the ocean
Phosphate and δ13C of DICin the Pacific Ocean.After Broecker and Peng, 1982 For info see Kroopnick, 1985
![Page 12: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/12.jpg)
δ13C of DIC – vertical and meridionalgradients
ATLANTIC
PACIFIC
Kroopnick, 1985
![Page 13: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/13.jpg)
Central Pacific DICand δ13C of DIC
What determinesthe DIC of surfaceseawater?
What determinesthe δ13C of surface DIC?
What happened here?
![Page 14: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/14.jpg)
(benthic foraminifera)
1:1
Oceanic δ13C on glacial-interglacial timescales
Benthic foraminifera recordthe δ13C of the DIC in whichthey grow.
Can take cores from1. different depths2. different locations
and reconstruct deepwater δ13Cthrough space and time
![Page 15: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/15.jpg)
Ninneman et al., 2002
Charles et al., 1996
Oceanic δ13C on glacial-interglacial timescales
So South Atlantic δ13Cwas lower during last glacial – NADW reduced!
Timing of δ13C shiftslook like Greenland ice!
![Page 16: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/16.jpg)
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: δ13C always reported in PDB
![Page 17: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/17.jpg)
green = reservoir size (1018g)red = fluxes (1018g/yr)blue = C isotopic value
* NOTE: pre-anthropogenic valuesFigure from William White, Cornell U.
Long Term Carbon Cycle
![Page 18: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/18.jpg)
C inputs-volcanism and
tectonics
![Page 19: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/19.jpg)
Weathering and CO2 drawdown:
![Page 20: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/20.jpg)
Uplift Weathering Hypothesis
![Page 21: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/21.jpg)
Evolution C4 plants
• Miocene Himalayas form• Increase in weathering, drawdown of CO2• Low CO2 conditions • Plants evolve to deal with low CO2• C4 plants
– Also more efficient in arid, hot regions
• C4 plants fix more C than C3 plants amplify global decline in CO2?
![Page 22: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/22.jpg)
![Page 23: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/23.jpg)
Osborne and Beerling, 2006
![Page 24: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/24.jpg)
Methane Hydrates and the PETM
![Page 25: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/25.jpg)
![Page 26: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/26.jpg)
Zachos et al., 2005
![Page 27: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/27.jpg)
![Page 28: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/28.jpg)
Zachos et al., 2005
-present-daylysocline = 3700-4500m
-shoaling of lysocline to <1500mrequired~4500GtC;entirefossil fuelreservoir!
![Page 29: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/29.jpg)
Catastrophic methane hydrate release captured in deep-sea cores?
-methane most depleted δ13C (-60‰ for biogenic, -40‰ for thermogenic)-frozen on every continental margin, but stability depends on T and P-methane is a greenhouse gas, can warm surface ocean, leading to more CH4 release, etc-can have medium-sized methane hydrate release from tectonic slope failure
Jim Kennet, “Clathrate Gun Hypothesis”, 2002
![Page 30: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/30.jpg)
-5‰
![Page 31: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/31.jpg)
![Page 32: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/32.jpg)
Model CO2 release’s impact on δ13C and temperature
![Page 33: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/33.jpg)
![Page 34: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/34.jpg)
Snowball Earth Hypothesis
• Earth’s entire surface frozen over
• Evidence for 3 times, maybe more
• Earlybetween 2200Mya and 650 Mya– (Proterozoic)
• Glacial sediment deposits at tropical latitudes
• Carbonate ‘caps’ on top of glacial sediments
![Page 35: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/35.jpg)
![Page 36: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/36.jpg)
How did it happen?
• Initial cooling + positive feedback– Supervolcano?– Orbital? (>60° ?)– Solar output?– Reduction in Greenhouse Gases?– Tropical continental position reflect more light
back to space?
• Feedback: albedo
![Page 37: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/37.jpg)
How did we get out of it?
• Plate tectonics– Volcanism—massive buildup of CO2– And no weathering to draw it down
• Massive Greenhouse following Massive Icehouse– Surge in weathering of tropical continents– Increase alkalinity– Deposition of carbonate ‘caps’
![Page 38: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/38.jpg)
![Page 39: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/39.jpg)
Snowball Earth Hypothesis
• Major excursions in δ13C in geologic record
• Seen around world in conjunction with geologic transitions
• Crucial for acceptance of global events
• Lots of variability in marine δ13C, more than today
![Page 40: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/40.jpg)
![Page 41: Carbon isotopes in the biosphere10/23/12 and geologic record](https://reader030.vdocuments.pub/reader030/viewer/2022012313/568146b9550346895db3e7ae/html5/thumbnails/41.jpg)
Decline in δ13C prior to glaciationsδ1
3C
‰ V
PD
B
δ13 C
‰ V
PD
B
Halverson et al., 2006