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

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

2. Grassland composition varies with climate %C4 = -0.9837 + 0.000594 (MAP) + 1.3528(JJA/MAP) + 0.2710 (lnMAT) Regression from Paruelo & Lauenroth (1996) Shift in C4 abundance The modern prairie is a C4-dominated grassland Map from Tieszen et al. (1997)

3. 13C shifts with change in plants Soil isotopes Biomass (STATGO)

4. 13C of soils and roots vs. depth von Fischer et al. 2008

5. 13C shifts with change in plants

6. 13C shifts with climate

7. LGM (180 ppm) C3-to-C4 balance is also affected by pCO2 C3 plants Crossover Temperature Quantum Yield (moles C fixed per photon absorbed) C4 plants Today (360 ppm) 3 6 9 12 15 18 21 24 27 30 Temperature (°C)

9. 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 C3-to-C4 balance

10. Why Texus? Climate means from 1931-1990 From New et al. (2000) Archived at www.ipcc-ddc.cru.uea.ac.uk

11. From Diamond et al. 1987 Texas vegetation today Another question: Were the plains and plateau regions covered by a boreal forest at the LGM?

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

14. Initial conclusions from isotope studies of Texas mammals No changes in mean δ13C value through time (ANOVA). Bison and mammoths are grazers. They can be used to monitor C3 to C4 balance on Pleistocene grasslands. Mastodons are browsers. Their presence suggests tree cover. 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. • 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.

15. Mammuthus Bison Mammut present %C4 Grass from Regression Model Holocene 0-10 Ka Post-LGM 10-15 Ka %C4 plants in grazer diets LGM 25-15 Ka 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)

17. Quaternary Prairies from animals Pleistocene horses were mixed feeders, not grazers. Despite climate change, %C4 biomass is remarkably constant through time. Always lots of C4 biomass on plains and plateaus and no mastodons. No LGM boreal forest in the region. 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

18. Quaternary Prairies from soils

19. Quaternary Prairies from soils

20. δ13C 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: 163-166.

21. Diet shifts in Mio-Pliocene Mammals Cerling et al. (1997)

22. 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)

23. 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)

24. Paleosol localities in the Central and Southern Great Plains

27. Modern C3 soilswith <100 mm precipitation

28. δ13C values of Great Plainspaleosol carbonates n = 274

29. δ13C values of Great Plainspaleosol carbonates n = 274

30. δ13C values of Great Plainspaleosol organics n = 20

31. δ13C values of Great Plainspaleosol organics n = 20

32. Isotopic evidence from new Great Plains faunas

33. Toto, I have a feeling we're not in Asia anymore. CO2 drop or climate change?

34. Globally synchronous at 7 Ma? Other sections in East Africa Levin et al. (2004) Age (Ma) d13C (VPDB)

35. A late Miocene drop in pCO2? Based on d13C records in organic biomarkers Pagani et al. (1999) Pearson & Palmer (2000)

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