Applications: Carbon Isotopes in SoilsApplications: Carbon Isotopes in Soils(w/ a digression on animals)(w/ a digression on animals)
Grassland composition varies with climate
Map from Tieszen et al. (1997)
Shift in C4 abundance
%C4 = -0.9837 + 0.000594 (MAP) + 1.3528(JJA/MAP) + 0.2710 (lnMAT)
Regression from Paruelo & Lauenroth (1996)
The modern prairie is aC4-dominated grassland
13C shifts with change in plants
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Biomass (STATGO)
Soil isotopes
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13C of soils and roots vs. depth
von Fischer et al. 2008
13C shifts with change in plants
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13C shifts with climate
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C3-to-C4 balance is also affected by pCO2
QuantumYield
(moles C fixed perphoton absorbed)
Temperature (°C)
3 6 9 12 15 18 21 24 27 30
C4 plants
C3 plants
Crossover Temperature
Today (360 ppm)
LGM (180 ppm)
Two questions about Great Plains ecosystems
At the LGM, was there less C4 biomass (because of lower temperatures) or more C4 biomass (because of lower pCO2)?
When (and why) did C4 grass come to dominate Great Plains ecosystems?
Use isotopes in animals and soils to track CUse isotopes in animals and soils to track C33-to-C-to-C44 balance balance
Why Texus?Why Texus?
Climate means from 1931-1990Climate means from 1931-1990From New et al. (2000)From New et al. (2000)Archived at www.ipcc-ddc.cru.uea.ac.ukArchived at www.ipcc-ddc.cru.uea.ac.uk
106°W 104°W 102°W 100°W 98°W 96°W 94°W
26°N
28°N
30°N
32°N
OKLAHOMA
MEXICO
TEXAS
Trans PecosEdwardsPlateau
RollingPlains
S. TexasBrushland
PineyWoods
LlanoUplift
Gulf CoastMarsh&Prairies
BP
34°N
36°N
NEW MEXICO
N
HighPlains
High Plains
From Diamond et al. 1987
Another question: Were the plains and plateau regions covered by a boreal forest at the LGM?
Texasvegetation
today
Holocene - Late Glacial
Last GlacialMaximum
Pre-LGM
Proboscideans
Holocene bison
Ingelside horses
Horses - Bison
Initial conclusions from isotope studies of Texas mammals
1) No changes in mean δ13C value through time (ANOVA).
1) Bison and mammoths are grazers. They can be used to monitor C3 to C4 balance on Pleistocene grasslands.
2) Mastodons are browsers. Their presence suggests tree cover.
3) Pleistocene horses ate lots of C3 vegetation, even when bison and mammoths had ~100% C4 diets. Horses were mixed feeders.
What's next?Compare %C4 from mammals to values simulated via modeling.
1) Use Quaternary climate model output, and estimate %C4 biomass using the Regression Equation.
2) Use the same climate model output, but estimate %C4 biomass as the percentage of growing season months that are above the appropriate Crossover Temperature.
Holocene0-10 Ka
Post-LGM10-15 Ka
LGM25-15 Ka
%C4 Grass from Regression Model
%C4 plants in grazer dietsMammuthus
Bison
Mammut present
Holocene model driven by modern climate data from New et al. (2000). LGM and Post-LGM models driven by GCM output from Kutzbach et al. (1996)(archived at www.ngdc.noaa.gov/paleo/paleo.html)
Quaternary Prairies from animals
1) Pleistocene horses were mixed feeders, not grazers.
2) Despite climate change, %C4 biomass is remarkably constant through time.
3) Always lots of C4 biomass on plains and plateaus and no mastodons. No LGM boreal forest in the region.
4) Only climate-vegetation models that account for changes in pCO2 as well as temperature provide reasonable %C4 estimates in parts of the Quaternary with different atmospheric compositions.
Koch et al. (2004) P3
Quaternary Prairies from soils
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Quaternary Prairies from soils
δ13C of paleosol carbonates from Pakistan
Quade et al. (1989)Development of theAsian monsoon revealed by marked ecological shift during the latest Miocene in northern Pakistan. Nature 342: 163-166.
Diet shifts in Mio-Pliocene Mammals
Cerling et al. (1997)
Isotopic evidence for dietary change in Great Plains horses
• Prior to the late Miocene, all horses ate mostly C3 plants
• 1st evidence for C4-dominated diets is at 6.6 Ma
• After 6.6 Ma, horses from Texas to Nebraska had a wide range of diets
Passey et al. (2002)
Isotopic evidence for dietary change in Great Plains horses
• Prior to the late Miocene, all horses at mostly C3 plants
• 1st evidence for C4-dominated diets is at 6.6 Ma
• After 6.6 Ma, horses from Texas to Nebraska had a wide range of diets
Passey et al. (2002)
Paleosol localities in the Central and Southern Great
Plains
Modern C3 soilswith <100 mm precipitation
δ13C values of Great Plainspaleosol carbonates
n = 274
δ13C values of Great Plainspaleosol carbonates
n = 274
δ13C values of Great Plainspaleosol organics
n = 20
δ13C values of Great Plainspaleosol organics
n = 20
Isotopic evidence from new Great Plains faunas
Toto, I have a feeling we're not in
Asia anymore.
CO2 drop or climate change?
Globally synchronous at 7 Ma?
13C (VPDB)
Ag
e (M
a) Other sections inEast Africa
Levin et al. (2004)
A late Miocene drop in pCO2?
Pagani et al. (1999)
Based on 13Crecords in organic biomarkers
Pearson & Palmer (2000)
0123450
10
20
30
40
50
60
70
Plt.
Age(Ma)
40 8 12
01 2 3-1
18 (O ‰) 13 (C ‰)
(Temperature° )C
- K T Boundary
LPTM or IETM
. E Eocene Climatic Optimum
Zachos et al. (2001)
Decrease in MAT.
Increase in seasonality.
Decrease in length of growing season.
Loss of winter growing season.