B32C-03
Thermochemical 14C Spectra and Carbon Turnover Time in Soils – a (Changing?) Latitudinal Gradient?

Wednesday, 16 December 2015: 10:50
2008 (Moscone West)
Brad E Rosenheim, University of South Florida Tampa, College of Marine Science, Saint Petersburg, FL, United States, Lael Vetter, Tulane University of Louisiana, New Orleans, LA, United States, Valier Galy, Woods Hole Oceanographic Institution, Marine Chemistry & Geochemistry, Woods Hole, MA, United States, Alain F Plante, University of Pennsylvania, Earth & Environmental Science, Philadelphia, PA, United States, Gesine Mollenhauer, Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, Bremerhaven, Germany, Jordon Dennis Hemingway, Massachusetts Institute of Technology, Earth, Atmospheric & Planetary Science, Cambridge, MA, United States, Katherine E Grant, Cornell University, Ithaca, NY, United States and Louis A Derry, Cornell University, Earth and Atmospheric Sciences, Ithaca, NY, United States
Abstract:
Organic carbon in soils can take on many chemical forms, cycle through different processes, and have different radiocarbon ages. In fact, measurement of different 14C ages in different chemical pools of soil organic carbon (SOC) has demonstrated that the radiocarbon “age” of SOC is more accurately discussed as the turnover time – a measure of the time it takes for SOC to cycle through a specific pool of carbon. Much has been learned, and is still being learned, about SOC turnover times by measuring ages of discrete reservoirs cycling over a continuum of time scales from minutes to millennia. Coupled measurements of radiocarbon age and thermochemical stability of SOC provide a novel approach to deconvoluting SOC turnover times from all present thermochemical reservoirs. We present results over a latitudinal gradient that relate thermochemical radiocarbon spectra to SOC turnover. From subtropical and temperate latitudes, radiocarbon spectra are nearly constant over the continuum of thermochemical stabilities. Contrast is evident at high latitudes, and where inputs of carbon from lateral transport and/or bedrock are high. In the active layer of soil from Svalbard, radiocarbon spectra span time scales of 102 – 105 14C y while in soil mineral horizons from Taiwan radiocarbon spectra varied between 4,000 and 13,000 14C y . Thus, as polar regions shrink and temperate/subtropical regions expand, thermochemical radiocarbon spectra provide a potential proxy for changes in SOC turnover time. Much remains to be investigated, however, before linking our observations to latitude. If the relationship holds, incorporation of such data into climate models enable more constraint on scenarios for anthropogenic warming such as the IPCC.

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