We present a model to resolve differences in soil-respired CO
2 and productivity, actual evapotranspiration (AET), and aridity across penecontemporaneous Middle and Late Permian landscapes by using the δ
13C values of co-existing pedogenic calcite and organic matter. Soil-respired CO
2 may be estimated by the following equation: C
S = C
A*(δ
13C
A(CC)-δ
13C
O(CC))/(δ
13C
m(CC)-δ
13C
O(CC)), where C
S and C
Aare values (ppmV) of CO
2in the soil and troposphere, respectively, δ
13C
A(CC) and δ
13C
O(CC) are δ
13C values of calcite formed only from CO
2 derived from oxidation of in-situ oxidation of organic matter and tropospheric CO
2 respectively, and δ
13C
m(CC) is the δ
13C value of paleosol calcite. δ
13C
m(CC) is measured directly; δ
13C
A(CC) and δ
13C
O(CC) may be estimated by δ
13 values of contemporaneous marine calcite and in-situ paleosol organic matter, respectively. If C
A is known through independent proxies, then C
S may be reported in terms of quantitative values. Alternatively, C
S may alternatively be reported as a proportionality among populations of penecontemporaneous paleosol profiles. Middle and Late Permian paleosol calcite δ
13C values collected thus far range from -3±1 to -12±1, whereas organic matter δ
13C values exhibit relatively little variability. These results indicate a broad range of soil PCO
2 across the Middle and Late Permian landscapes.
Soil-respired CO2 is strongly correlated with actual evapotranspiration (AET) from the soil. Soils with low AET values occur in dry (or very cold) climates with low biological productivity. Thus, soil PCO2 estimates from co-existing paleosol calcite and organic matter permit determination of which landscapes were most arid, and characterized by limited biological productivity. Results indicate that lowest soil PCO2 occurred in subtropical landscapes, continental interiors of Pangea. These results indicate those sites were among the most arid landscapes upon the supercontinent. These isotope-based results agree well with AET and Biome estimates derived from Global Circulation Models.