Age Distribution of the Particulate Organic Carbon (POC) Discharged from Small Mountainous Rivers-- the Influence of Sediment Yield and Soil Residence Time

摘要 短小的山地河流在向北美西缘和整个海洋提供沉积物的河流中占主导地位。 由于这些主动边缘系统中景观剥蚀速度快且沉积物储存最少，排放的颗粒有机碳（POC）与被动边缘较大河流输送的颗粒有机碳（POC）不同。 最近对加利福尼亚州两条河流的调查表明，它们携带着现代和古代颗粒有机碳（POC）的双峰混合物，几乎同样来自现存植被和隆起沉积岩的干酪根。 初步估计，在发生显着老化之前或干酪根完全氧化并被现代材料取代之前，这些系统中的土壤就会受到侵蚀。 根据这些初步结果，河流携带的现代、古代和中年 POC 之间的平衡被假设取决于颗粒在风化层中的停留时间。 为了检验这一假设，本次调查将描述六条河流的悬浮 POC 负荷的特征，这些河流的产沙量呈现出三个数量级的范围。 四条河流（Siuslaw、Noyo、Russian 和 Eel）流经加利福尼亚州北部和俄勒冈州的部分地区。 选择新西兰北岛的怀帕阿河和怀阿普河是因为它们的沉积物产量极高。 基岩 POC 也将在每个流域中进行表征。 主要测量 OC 含量、13C/12C(d13C) 和 14C/12C (?14C) 将在大块样品以及密度和尺寸分级子样品上进行，以确定干酪根和现代碳含量。 将对鳗鱼流域的土壤剖面进行更多研究，以进一步描绘风化层中的风化和有机碳替代过程。 POC 池从基岩 C 到现代地表物质的演变将在厚层中进行研究，以与之前薄土剖面的结果进行对比。 这项研究的结果将进一步了解控制有机碳从流域输送到海洋的数量和特征的过程。 这项研究还解决了长期生物地球化学循环中的一个关键问题，即如何回收先前埋藏的有机碳。 这项调查可以显着改善对过去环境的沉积有机地球化学记录的解释，特别是活动边缘的沉积有机地球化学记录。

AbstractShort, mountainous rivers dominate the fluvial supply of sediment to the western margin of North America and to the oceans in general. As a result of rapid rates of landscape denudation and minimal sediment storage in these active margin systems, the particulate organic carbon (POC) discharged differs from that transported by larger rivers on passive margins. Recent investigations of two rivers in California indicate they carry a bimodal mixture of modern and ancient particulate organic carbon (POC), derived almost equally from extant vegetation and from the kerogen of uplifted sedimentary rocks. To a first approximation, soils are eroded in these systems before significant aging occurs or before the kerogen can be completely oxidized and replaced by modern material. Based on these preliminary results, the balance between modern, ancient, and intermediate-aged POC carried by rivers is hypothesized to depend on the residence time of particles in the regolith. To test this hypothesis, this investigation will characterize the suspended POC loads of six rivers that exhibit a three-order range of magnitude in sediment yield. Four rivers (Siuslaw, Noyo, Russian, and Eel) drain portions of northern California and Oregon. The Waipaoa and Waiapu rivers on the north island of New Zealand were chosen because of their extremely high sediment yields. Bedrock POC will also be characterized in each of the watersheds. The principle measurements, OC content, 13C/12C(d13C), and 14C/12C (?14C), will be made on bulk samples, as well as density- and size-fractionated subsamples, to determine the kerogen and modern C contents. Additional studies of soil profiles in the Eel watershed will be conducted to further delineate weathering and OC replacement processes in the regolith. The evolution of the POC pool from bedrock C to modern surficial material will be studied in thick horizons, to contrast with previous results from thin soil profiles. The results of this study will further understanding of the processes that regulate the quantity and character of OC transported from drainage basins to the ocean. This study also addresses a key issue in the long-term biogeochemical cycle, namely how previously buried OC is recycled. Interpretation of the sedimentary organic geochemical record of past environments, particularly on active margins, could be significantly improved by this investigation.