Drained thaw-lake basin soil characteristics of cores from Barrow, Alaska

Arctic soils contain a large fraction of Earth's stored carbon. Temperature increases in the Arctic may enhance decomposition of this stored carbon, shifting the role of Arctic soils from a net sink to a new source of atmospheric CO2. Predicting the impact of Arctic warming on soil carbon reserves requires knowledge of the composition of the stored organic matter. Here, we employ solid state 13C nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared-photoacoustic spectroscopy (FTIR-PAS) to investigate the chemical composition of soil organic matter collected from drained thaw-lake basins ranging in age from 0 to 5500 years before present (y BP). The 13C NMR and FTIR-PAS data were largely congruent. Surface horizons contain relatively large amounts of O-alkyl carbon, suggesting that the soil organic matter is rich in labile constituents. Soil organic matter decreases with depth with the relative amounts of O-alkyl carbon decreasing and aromatic carbon increasing. These data indicate that lower horizons are in a more advanced stage of decomposition than upper horizons. Nonetheless, a substantial fraction of carbon in lower horizons, even for ancient thaw-lake basins (2000-5500 y BP), is present as O-alkyl carbon reflecting the preservation of intrinsically labile organic matter constituents. Climate change-induced increases in the depth of the soil active layer are expected to accelerate the depletion of this carbon.北极土壤储存着地球总量可观的固存碳。北极地区升温可能会强化这类固存碳的分解过程，使北极土壤从大气CO₂的净汇转变为大气CO₂的新增源。要预测北极变暖对土壤碳储量的影响，需明确其中固存有机质的化学组成。本研究采用固态13C核磁共振波谱法（solid state 13C nuclear magnetic resonance, NMR）与傅里叶变换红外光声光谱法（Fourier transform infrared-photoacoustic spectroscopy, FTIR-PAS），对取自形成年代跨度为0至5500距今年（y BP）的疏干融冻湖盆地的土壤有机质化学组成展开分析。13C NMR与FTIR-PAS的检测数据整体一致性良好。表层土层的氧烷基碳（O-alkyl carbon）相对含量较高，表明该区域土壤有机质富含易分解组分。土壤有机质含量随土层深度增加而降低，同时氧烷基碳的相对占比逐渐减少，芳香碳（aromatic carbon）的相对占比则逐步升高。上述数据表明，深层土壤有机质的分解成熟度高于表层土壤。尽管如此，深层土壤中仍有相当比例的碳以氧烷基碳形式存在；即使是形成年代久远的融冻湖盆地（2000至5500 y BP），其土壤中也保留了大量本征易分解的有机质组分。气候变化引发的土壤活动层深度增加，预计将加速这类碳库的耗竭。