|Huntington, T - USGS|
|Marion, D - USFS|
Submitted to: Trans American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: June 4, 1999
Publication Date: N/A
Technical Abstract: Global ecosystem modeling studies have suggested both decreases and increases in soil organic carbon (SOC) under climate changes expected to occur if atmospheric concentrations of CO2 double by about 2100. Current estimates are that mean annual temperature (MAT) will increase by about 3 degrees C by the year 2100. The reasons for the different predictions stem mfrom large uncertainties in the quantitative representation of the processes that control formation and decomposition of SOC. The critical question is whether increases in rates of decomposition, due to increases in temperature, will outweigh potential increases in net primary productivity (NPP) associated with increasing temperature and atmospheric CO2 concentrations. Insight into whether model predictions are reasonable can be obtained by examining the current distribution of SOC storage along climatic gradients. A regression analysis was conducted to determine the relationship between SOC in the surface 20 cm and MAT and mean annual precipitation (MAP) on cultivated, loess-derived soils along a latitudinal gradient from Louisiana to Minnesota. SOC was significantly correlated with MAT but was not correlated with MAP. SOC increased from about 2.6 kg carbon per meter squared in southern Mississippi to about 5.1 kg carbon per meter squared in southern Minnesota. Over this latitudinal range, MAT decreased from 18 to 7 deg C. This analysis and a previously published study for grassland soils suggest that a 3 degree C increase in MAT would result in decreases in SOC ranging from about 6 to 20 percent in the surface 20 cm. Larger percentage and absolute decreases in SOC are expected at more poleward latitudes based on current SOC storage and the exponential form of the regression of SOC and MAT.