Abstract The Paleocene-Eocene Thermal Maximum (PETM) warming event is marked by a negative carbon isotope excursion (CIE). The magnitude and shape of the CIE differs among carbon archives, but bulk organic carbon isotopes (δ13Corg) in terrestrial sections are often particularly variable and attenuated. Multiple lines of evidence from the Bighorn Basin, Wyoming, USA have revealed that extensive organic carbon degradation and increased refractory or allochthonous carbon inputs diminished the δ13Corg excursion magnitude. To test if this was a spatially widespread phenomenon and to understand possible underlying mechanisms, we examined the abundance of total organic carbon (%TOC) and polycyclic aromatic hydrocarbons (PAHs) as metrics of soil degradation at a neighboring terrestrial basin, the Piceance Basin in Colorado. Outcrop samples reveal both diminished %TOC and PAH concentrations across the Paleocene-Eocene boundary. Using PAHs as a proxy for intermediate refractory carbon, such as found in mineral soils, evidence from the Piceance Basin supports increased organic carbon degradation and greater proportions of refractory allochthonous carbon remaining. Correlations between %TOC and elemental oxides (e.g., Al2O3 and TiO2) suggest soil organic carbon was stabilized by its association with clay minerals. We hypothesize that decreased clay content in the soils (which reduced soil capacity to stabilize fresh carbon) and increased fluctuations in soil moisture (which destabilized older, refractory carbon), in conjunction with increased temperatures (which increased microbial decomposition rates), contributed to reduced soil organic matter preservation during the PETM. These mechanisms destabilized carbon on millennial timescales and, with sustained higher temperatures across the PETM (~150,000 years), increased soil carbon degradation persisted for tens of thousands of years.

中文翻译：

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美国Piceance盆地古新世-始新世热最大值期间土壤碳降解

摘要 古新世-始新世热最大值 (PETM) 变暖事件以负碳同位素偏移 (CIE) 为标志。CIE 的大小和形状因碳档案而异，但陆地剖面中的大块有机碳同位素 (δ13Corg) 通常特别可变且衰减。来自美国怀俄明州比格霍恩盆地的多条证据表明，广泛的有机碳降解和增加的难熔或外来碳输入减少了 δ13Corg 偏移量级。为了测试这是否是一种空间广泛的现象并了解可能的潜在机制，我们检查了总有机碳 (%TOC) 和多环芳烃 (PAH) 的丰度，作为邻近陆地盆地 Piceance 盆地的土壤退化指标。科罗拉多州。露头样品显示整个古新世-始新世边界的 %TOC 和 PAH 浓度均降低。使用多环芳烃作为中间难熔碳的替代物，例如在矿质土壤中发现的，来自 Piceance 盆地的证据支持有机碳降解增加和难熔外来碳的残留比例更大。%TOC 和元素氧化物（例如，Al2O3 和 TiO2）之间的相关性表明土壤有机碳通过其与粘土矿物的结合而稳定。我们假设土壤中粘土含量减少（这降低了土壤稳定新鲜碳的能力）和土壤水分波动增加（这会破坏旧的难熔碳），同时温度升高（这会增加微生物分解率），在PETM期间有助于减少土壤有机质保存。这些机制在千年时间尺度上破坏了碳的稳定性，并且随着整个 PETM（约 150,000 年）温度持续升高，土壤碳降解的增加持续了数万年。