Thomas G. Huntington Laurie J. Osher Leonard I Wassenaar Susan E. Trumbore Ronald Amundson Jennifer W. Harden Diane M. McKnight Sherry L. Schiff George R. Aiken W. Berry Lyons Ramon O. Aravena Jill Baron Yang Wang 1998 <p><span>This chapter reviews a number of applications of isotopic techniques for the investigation of carbon cycling processes. Carbon dioxide (C0</span>₂<span>) is an important greenhouse gas. Its concentration in the atmosphere has increased from an estimated 270 ppm at the beginning of the industrial revolution to &sim; 360 ppm at present. Climatic conditions and atmospheric C0</span>₂<span>&nbsp;concentration also influence isotopic discrimination during photosynthesis. Natural and anthropogenically induced variations in the carbon isotopic abundance can be exploited to investigate carbon transformations between pools on various time scales. It also discusses one of the isotopes of carbon, the&nbsp;</span>¹⁴<span>C, that is produced in the atmosphere by interactions of cosmic-ray produced neutrons with stable isotopes of nitrogen (N), oxygen (O), and carbon (C), and has a natural abundance in the atmosphere of &sim;1 atom&nbsp;</span>¹⁴<span>&nbsp;C per 10</span>¹²<span>&nbsp;atoms&nbsp;</span>¹²<span>C. The most important factor affecting the measured&nbsp;</span>¹⁴<span>C ages of soil organic matter is the rate of organic carbon cycling in soils. Differences in the dynamics of soil carbon among different soils or soil horizons will result in different soil organic&nbsp;</span>¹⁴<span>C signatures. As a result, the deviation of the measured&nbsp;</span>¹⁴<span>C age from the true age could differ significantly among different soils or soil horizons.</span></p> application/pdf 10.1016/B978-0-444-81546-0.50024-0 en Elsevier Carbon cycling in terrestrial environments: Chapter 17 chapter