Table S1.

Calculation of end-member δ13C values of soil organic matter for C313CC3) and C4 vegetation (δ13CC4) for the mid-Holocene and Last Glacial Maximum (LGM)

Factorδ13CC3, ‰δ13CC4, ‰Calculation basis and data sources
Mid-Holocene*
 Today's vegetation−26.7−12.8Ref. 30
 δ13Catm correction (+1.7‰)−25.0−11.1δ13C of atmospheric CO2: −8.06‰ for the present (Mauna Loa Observatory, 2000; ftp://aftp.cmdl.noaa.gov/data/trace_gases/co2c13/flask/surface/co2c13_mlo_surface-flask_1_sil_month.txt); −6.33‰ for the mid-Holocene (53)
 Degradation correction (+1.0‰)−24.0−10.1Refs. 17 and 54
LGM
 Today's vegetation−26.7−12.8Ref. 30
 δ13Catm correction (+1.6‰)−25.1−11.2δ13C of atmospheric CO2: −8.06‰ for the present (Mauna Loa Observatory, 2000; ftp://aftp.cmdl.noaa.gov/data/trace_gases/co2c13/flask/surface/co2c13_mlo_surface-flask_1_sil_month.txt); −6.46‰ for the LGM (53)
 Precipitation correction (C3: +0.6‰)−24.5−11.2∼150 mm lower in the LGM than at the present (55, 56); −0.40‰/100 mm for C3 plants and a negligible coefficient for C4 plants (30)
 Temperature correction (C3: −0.6‰)−25.1−11.26 °C lower in the LGM than at the present (56); 0.104‰/°C for C3 plants and no significant correlation for C4 plants (57)
 Degradation effect (+1.0‰)−24.1−10.2Refs. 17 and 54
  • * The climatic conditions in the mid-Holocene are assumed to be similar to the present, and thus the precipitation and temperature corrections for the mid-Holocene are ignored.