Applications: Carbon Isotopes in Soils (w/ a digression on animals)

Grassland composition varies with climate Map from Tieszen et al. (1997) Shift in C 4 abundance %C 4 = (MAP) (JJA/MAP) (lnMAT) Regression from Paruelo & Lauenroth (1996) The modern prairie is a C 4 -dominated grassland

 13 C shifts with change in plants Biomass (STATGO) Soil isotopes

 13 C of soils and roots vs. depth von Fischer et al. 2008

 13 C shifts with change in plants

 13 C shifts with climate

C 3 -to-C 4 balance is also affected by pCO 2 Quantum Yield (moles C fixed per photon absorbed) Temperature (°C) C 4 plants C 3 plants Crossover Temperature Today (360 ppm) LGM (180 ppm)

Two questions about Great Plains ecosystems At the LGM, was there less C 4 biomass (because of lower temperatures) or more C 4 biomass (because of lower pCO 2 )? When (and why) did C 4 grass come to dominate Great Plains ecosystems? Use isotopes in animals and soils to track C 3 -to-C 4 balance

Why Texus? Climate means from From New et al. (2000) Archived at

From Diamond et al Another question: Were the plains and plateau regions covered by a boreal forest at the LGM? Texas vegetation today

Holocene - Late Glacial Last Glacial Maximum Pre-LGM Proboscideans Holocene bison Ingelside horses Horses - Bison

Initial conclusions from isotope studies of Texas mammals 1)No changes in mean δ 13 C value through time (ANOVA). 2)Bison and mammoths are grazers. They can be used to monitor C 3 to C 4 balance on Pleistocene grasslands. 3)Mastodons are browsers. Their presence suggests tree cover. 4)Pleistocene horses ate lots of C 3 vegetation, even when bison and mammoths had ~100% C 4 diets. Horses were mixed feeders. What's next? Compare %C 4 from mammals to values simulated via modeling. 1)Use Quaternary climate model output, and estimate %C 4 biomass using the Regression Equation. 2)Use the same climate model output, but estimate %C 4 biomass as the percentage of growing season months that are above the appropriate Crossover Temperature.

Holocene 0-10 Ka Post-LGM Ka LGM Ka %C 4 Grass from Regression Model %C 4 plants in grazer diets Mammuthus 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

Quaternary Prairies from animals 1)Pleistocene horses were mixed feeders, not grazers. 2)Despite climate change, %C 4 biomass is remarkably constant through time. 3)Always lots of C 4 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 pCO 2 as well as temperature provide reasonable %C 4 estimates in parts of the Quaternary with different atmospheric compositions. Koch et al. (2004) P3

Quaternary Prairies from soils

δ 13 C of paleosol carbonates from Pakistan Quade et al. (1989) Development of the Asian monsoon revealed by marked ecological shift during the latest Miocene in northern Pakistan. Nature 342:

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 C 3 plants 1 st evidence for C 4 - 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 C 3 plants 1 st evidence for C 4 - 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 C 3 soils with <100 mm precipitation

δ 13 C values of Great Plains paleosol carbonates n = 274

δ 13 C values of Great Plains paleosol carbonates n = 274

δ 13 C values of Great Plains paleosol organics n = 20

δ 13 C values of Great Plains paleosol organics n = 20

Isotopic evidence from new Great Plains faunas

Toto, I have a feeling we're not in Asia anymore. CO 2 drop or climate change?

Globally synchronous at 7 Ma?  13 C (VPDB) Age (Ma) Other sections in East Africa Levin et al. (2004)

A late Miocene drop in pCO 2 ? Pagani et al. (1999) Based on  13 C records in organic biomarkers Pearson & Palmer (2000)

Zachos et al. (2001) Decrease in MAT. Increase in seasonality. Decrease in length of growing season. Loss of winter growing season.