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

摘要短而多山的河流主导着北美西部边缘和海洋的泥沙供应。由于这些主动边缘系统的景观剥蚀速度快，沉积物储量少，排放的颗粒有机碳（POC）不同于被动边缘较大河流的输送。最近对加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，几乎同样来自现存的植被和隆起的沉积岩的干酪根。近似地说，在这些系统中，土壤在显著老化或干酪根完全氧化并被现代物质取代之前就被侵蚀了。基于这些初步结果，我们假设河流携带的现代、古代和中期POC之间的平衡取决于颗粒在风化层中的停留时间。为了验证这一假设，本研究将对6条河流的悬浮POC负荷进行表征，这些河流在产沙量方面表现出三个量级的范围。四条河流（苏斯拉夫河、诺约河、俄罗斯河和鳗鱼河）流经加州北部和俄勒冈州的部分地区。新西兰北岛的怀帕阿河和怀亚普河之所以被选中，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。原理测量，OC含量，13C/12C(d13C)，和14C/12C (？14C)，将在散装样品以及密度和尺寸分馏亚样品上进行，以确定干酪根和现代C含量。将对鳗鱼流域的土壤剖面进行进一步的研究，以进一步描绘风化层中的风化和有机碳替换过程。将在较厚的地层中研究从基岩C到现代表层物质的POC池的演化，并与先前的薄土壤剖面结果进行对比。本研究结果将有助于进一步了解从流域向海洋输送OC的数量和特征的调节过程。本研究还解决了长期生物地球化学循环中的一个关键问题，即以前埋藏的有机碳是如何回收的。通过这次调查，可以大大提高对过去环境，特别是活动边缘沉积有机地球化学记录的解释。

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.