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

摘要短时间内，山区河流主导着北美西部边缘和整个海洋的河流沉积物供应。由于这些主动边缘系统的快速景观剥蚀和极少的沉积物储存，排放的颗粒有机碳(POC)不同于被动边缘上较大的河流所输送的颗粒有机碳。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，它们几乎同样来自现存的植被和隆起的沉积岩的干酪根。大致来说，在这些系统中，土壤在显著老化之前或干酪根完全氧化并被现代材料取代之前就被侵蚀了。根据这些初步结果，推测河流携带的现代、古代和中年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，这项调查将表征六条河流的悬浮POC负荷，这些河流的泥沙产量呈现出三个数量级的范围。四条河流(苏斯瓦夫、诺约河、俄罗斯河和鳗鱼)排干了加利福尼亚州北部和俄勒冈州的部分地区。新西兰北部岛屿上的怀保阿河和怀阿普河之所以被选中，是因为它们的泥沙产量极高。基岩POC还将在每个分水岭中进行表征。将对大样以及密度和粒度分馏的亚样进行有机碳含量、13C/12C(D13C)和14C/12C(？14C)的基本测量，以确定干酪根和现代碳的含量。将对鳗鱼分水岭的土壤剖面进行更多的研究，以进一步描绘风化和有机碳在风化层中的置换过程。POC气藏从基岩C到现代地表物质的演化将在厚层中进行研究，以与以前薄土壤剖面的结果进行对比。这项研究的结果将进一步了解调节有机碳从流域向海洋输送的数量和性质的过程。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，即以前埋藏的有机碳如何被循环利用。通过这次调查，可以大大改进对过去环境的沉积有机地球化学记录的解释，特别是在活动边缘。

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.