Evaluation of environmental change in the sediments under hypoxia revealed by non-destructive speciation of elements.

缺氧是含有少量溶解氧的水团。本研究假设缺氧历史记录在底部沉积物上，通过沉积物的纵向分析来厘清过去缺氧的规模。东京湾疏海沟的面积和深度最大，且存在较强的缺氧现象。因此，这一区域适合用来估计过去的缺氧情况。岩心沉积物收集自疏浚的海沟和未疏浚的海床作为参考点。我们根据沉积年龄对每一层沉积物进行了非破坏性状态分析的Moessbauer光谱和x射线吸收精细结构。结果表明，疏浚海沟的沉积环境具有一定的特殊性，且缺氧规模呈减小趋势。同时，关注氧化还原敏感元素的相对浓度变化，评价沉积时的氧化还原条件。

Hypoxia is water mass with little dissolved oxygen. This research aims at clarifying the scale of past hypoxia by the vertical analysis of sediments, assuming that the history of hypoxia is recorded on the bottom sediment. The dredged trench off Makuhari in Tokyo Bay has the maximum area and depth, and strong hypoxia has been observed there. Therefore, this area is suitable for an estimation of past hypoxia.The core sediments were collected from dredged trenches and non-dredged seabed as a reference site. We have applied Moessbauer spectroscopy and X-ray absorption fine structure, which are non-destructive state analysis, to every layer of the sediments obtained according to the sedimentation age. As a result, it is proved that the sedimentation environment of dredged trenches was specific and that the scale of hypoxia was decreasing. Moreover, paying attention to a relative concentration change of redox-sensitive elements, redox conditions at the time of deposition was evaluated.