224Ra:228Th disequilibrium in coastal sediments: Implications for solute transfer across the sediment-water interface
224Ra:228Th disequilibrium in coastal sediments: Implications for solute transfer across the sediment-water interface
复制标题
沿海沉积物中的 224Ra:228Th 不平衡：对沉积物-水界面溶质转移的影响
DOI：
10.1016/j.gca.2013.09.029
复制
发表时间：
2014-01-15
影响因子：
5
通讯作者：
Dai, Minhan
中科院分区：
文献类型：
--
作者：
Cai, Pinghe;Shi, Xiangming;Dai, Minhan
我们利用沉积物中的Ra-224/Th-228不平衡来研究调节沉积物-水界面溶质迁移的过程。2011年8月15 - 24日，利用延迟符合计数器对长江口表层0-20 cm沉积物中溶解态和表面结合态Ra-224和Th-228的深度剖面进行了测量。沿着Ra-224和Th-228，收集Th-234的深度剖面以确定沉积物中的生物扰动率。在大多数研究中心，Ra-224相对于Th-228的显著不足在上部0-10 cm中观察到。与此相反，Ra-224相对于Th-228过量，在上0-5厘米在河口，可能是由于Ra-224的再分配从中盐度区域。通过使用一般成岩方程对沉积物中的Ra-224深度剖面进行建模，我们证明，在大多数情况下，分子扩散和生物扰动一起只能占Ra-224测量通量的20-30%。我们的结论是，其他机制，特别是灌溉，必须调用来解释剩余的70%的Ra-224相对于Th-228的观测偏差。基于沉积物中Ra-224/Th-228不平衡和早期研究者提出的灌溉增加交换表面积的概念，我们提出了一种新的方法-Ra-224/Th-228不平衡方法来量化沉积物-水界面上其他溶解物种的转移速率。我们已经利用这种新的方法来确定溶解的O-2的底栖动物的消耗率。结果表明，底栖动物的消耗是长江口溶解氧的重要损失项，也是导致长江口缺氧的重要机制之一。(C)2013爱思唯尔有限公司保留所有权利。
We utilized Ra-224/Th-228 disequilibrium in the sediment to investigate processes that regulate solute transfer across the sediment-water interface. Depth profiles of dissolved and surface-bound Ra-224 and Th-228 in the upper 0-20 cm sediment column were measured using a delayed coincidence counter during a cruise to the Yangtze estuary from 15 to 24 August 2011. Along with Ra-224 and Th-228, depth profiles of Th-234 were collected to determine the bioturbation rate in the sediment. At most study sites, a significant deficit of Ra-224 relative to Th-228 was observed in the upper 0-10 cm. In contrast, Ra-224 was in excess with respect to Th-228 in the upper 0-5 cm at the river mouth, possibly due to redistribution of Ra-224 from the mid-salinity region. By modeling the Ra-224 depth profiles in the sediment using the general diagenetic equation, we demonstrated that in most cases molecular diffusion and bioturbation together can account for only similar to 20-30% of the measured flux of Ra-224. We concluded that other mechanisms, especially irrigation, must be invoked to explain the remnant 70% of the observed deviation of Ra-224 relative to Th-228. On the basis of the Ra-224/Th-228 disequilibrium in the sediment and a concept of increased surface area for exchange by irrigation as developed by early investigators, we proposed a new approach - the Ra-224/Th-228 disequilibrium approach to quantify the transfer rate of other dissolved species across the sediment-water interface. We have utilized this new approach to determine the benthic consumption rate of dissolved O-2. The result reveals that benthic consumption is an important loss term of dissolved O-2 in the Yangtze estuary and must be considered as one of the mechanisms that lead to hypoxia in this area. (C) 2013 Elsevier Ltd. All rights reserved.