Short organic carbon turnover time and narrow 14C age spectra in early Holocene wetland paleosols
Short organic carbon turnover time and narrow 14C age spectra in early Holocene wetland paleosols
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DOI：
10.1002/2016gc006526
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发表时间：
2017-01
期刊：
影响因子：
3.7
通讯作者：
L. Vetter;B. Rosenheim;A. Fernandez;T. Törnqvist
中科院分区：
文献类型：
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作者：
L. Vetter;B. Rosenheim;A. Fernandez;T. Törnqvist
古土壤包含了土壤活跃形成时土壤有机碳周转速率的信息。然而，这种时间信息往往是难以解释没有严格的地层控制的古土壤的年龄。在这里，我们应用斜坡热解/氧化（斜坡PyrOx）14 C分析，以评估从密西西比三角洲在美国路易斯安那州东南部的海侵早全新世古土壤的年龄谱。我们发现14 C年龄谱从土壤有机质（SOM）在古土壤和覆盖的基底泥炭，代表年龄的变异性接近，或仅略大于，14 C测量的分析不确定性，尽管不同来源的碳可能不同的年龄。这种年龄谱以前在沉积记录中没有观察到。在这里，他们表明，有力的土壤碳周转埋葬前，在整个热化学谱的SOM内均匀的14 C年龄。古土壤和上覆泥炭的斜坡PyrOx的加权体14 C年龄在分析和过程相关的不确定性内是相同的，并证实了来自上覆泥炭的木炭碎片和植物宏体化石的14 C年龄。从斜PyrOx年龄谱的最年轻的年龄也可能被应用为地层埋藏年龄的计时器。我们的研究结果表明，这些土壤中的碳相对于外来碳的输入快速周转（约300年），表明不同土壤组分的14 C年龄与热化学稳定性无关，而是反映了活跃的周转过程。古土壤和泥炭14 C年龄的同时也表明，成壤过程与沿海沼泽的发展，和启动效应可能掩盖了海平面上升过程中外来碳输入的信号。
Paleosols contain information about the rates of soil organic carbon turnover when the soil was actively forming. However, this temporal information is often difficult to interpret without tight stratigraphic control on the age of the paleosol. Here we apply ramped pyrolysis/oxidation (Ramped PyrOx) 14C analyses to evaluate age spectra of transgressive early Holocene paleosols from the Mississippi Delta in southeastern Louisiana, USA. We find 14C age spectra from soil organic matter (SOM) in both paleosols and overlying basal peats that represent variability in age that is close to, or only slightly greater than, analytical uncertainty of 14C measurements, despite different sources of carbon with likely disparate ages. Such age spectra have not previously been observed in the sedimentary record. Here they indicate vigorous soil carbon turnover prior to burial, which homogenized 14C ages within SOM across the entire thermochemical spectrum. The weighted bulk 14C ages from Ramped PyrOx of paleosols and overlying peats are identical within analytical and process‐associated uncertainty, and corroborate 14C ages from charcoal fragments and plant macrofossils from the overlying peat. The youngest ages from Ramped PyrOx age spectra may also potentially be applied as chronometers for stratigraphic burial ages. Our results suggest rapid turnover (≪300 years) of carbon in these soils relative to input of allochthonous carbon, indicating that the 14C age of different soil components is decoupled from thermochemical stability and instead reflects vigorous turnover processes. The concurrence of paleosol and peat 14C ages also suggests that pedogenic processes were linked with the development of coastal marshes, and that the priming effect potentially masked the signal of allochthonous carbon inputs during sea level rise.