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首页> 外文期刊>Marine Geology >Using multi-radiotracer techniques to better understand sedimentary dynamics of reworked muds in the Changjiang River estuary and inner shelf of East China Sea
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Using multi-radiotracer techniques to better understand sedimentary dynamics of reworked muds in the Changjiang River estuary and inner shelf of East China Sea

机译：使用多放射性示踪技术更好地了解长江口和东海内陆陆架返修泥浆的沉积动力学

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Reworked muds, including mobile muds, resuspended sediments, and bio-mixed muds are ephemeral layers in the benthic boundary of large-river delta-front estuaries (LDEs). In this study, multiple radiotracers (Pb-210, Cs-137, Th-234, Be-7, U-235, Th-228, R-228 Ra-226 and K-40) were combined to evaluate the sedimentary dynamics of the mud belt on the inner shelf of the East China Sea (ECS) adjacent to the Changflang River Estuary. We first categorized eight types of typical Pb-210 profiles in marine sediments, and specified which ones could be used as possible evidence of reworked muds. The types of Pb-210 profiles observed in previous studies and this study were then used to examine the depth distribution of reworked mud layers of the benthic boundary of ECS. We found that reworked mud depth in the along-shore mud belt of the inner shelf of ECS was deeper than those in the outer shelf and slope area, reaching up to 150 cm deep in the Changjiang River LDE, and up to 50 cm deep in the Zhejiang-Fujian coast mud area. Sediment core tracer profiles also showed that the reworked mud layer could be further divided into several sub-layers with distinct redox conditions and microbe (sulfate-reducing bacterial) abundance. SRB abundance intensively fluctuated with changing redox environment, and larger abundance values were usually observed in anoxic conditions. Based on Be-7 and Th-234, the top layer (ca. 2-4 cm thick) was the most modern and active zone, showing evidence of reworking on seasonal timescales. The deeper sections of the reworked mud layer were generally modified over longer timescale (years) which were examined using the more long-lived tracers, e.g., Cs-137, Th-228. and Ra-228/Ra-226 ratio. We found for the first time in this region that age of the reworked layers was usually much younger than underlying accumulating (burial) layers. We posit that this multi-radionuclide approach is critical for evaluating the complex biogeochemical sediment record on delta-front estuaries of large rivers subject to changing climate conditions and human impacts over the last several centuries. (C) 2015 Elsevier B.V. All rights reserved.
机译：重造的泥浆，包括流动泥浆，重悬的沉积物和生物混合泥浆，是大河三角洲前缘河口（LDE）底栖边界中的短暂层。在这项研究中，结合了多种放射性示踪剂（Pb-210，Cs-137，Th-234，Be-7，U-235，Th-228，R-228 Ra-226和K-40）评估了沉积物的动力学。东中国海（ECS）内陆与长江长河口相邻的泥带。我们首先对海洋沉积物中的八种典型Pb-210剖面进行了分类，并指定了哪些可以用作返工泥浆的可能证据。在先前的研究和本研究中观察到的Pb-210剖面的类型随后被用于检查ECS底栖边界的返工泥层的深度分布。我们发现，ECS内陆支架沿岸泥带的返工泥浆深度比外陆支架和斜坡区深，长江中游支配区的泥浆深达150 cm，长江支流的泥浆深达50 cm。浙闽沿海泥区。沉积物芯示踪剂剖面还显示，可以将再加工的泥层进一步分为具有不同氧化还原条件和微生物（减少硫酸盐的细菌）含量的几个子层。 SRB的丰度随着氧化还原环境的变化而剧烈波动，通常在缺氧条件下观察到较大的丰度值。基于Be-7和Th-234，顶层（约2-4厘米厚）是最现代，最活跃的区域，显示出在季节性时标上进行返工的证据。返工泥层的较深部分通常会在较长的时间尺度（年）内进行修改，然后使用寿命更长的示踪剂（例如Cs-137，Th-228）进行检查。和Ra-228 / Ra-226比率。我们在该地区首次发现，返工层的年龄通常比基础堆积（埋葬）层年轻得多。我们认为，这种多放射性核素方法对于评估大型河流三角洲前缘河口复杂的生物地球化学沉积物记录至关重要，在过去的几个世纪中，这些河流受到气候条件的变化和人类的影响。 （C）2015 Elsevier B.V.保留所有权利。

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