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.