Establishment of an estimation method of past aquatic events with records on shells and development of utilization for the rehabilitation of environment

本研究的目的是使过去根据贝壳的生长线来估计缺氧等水生环境的可能性成为可能。尽管有初步计划，但由于 14C 测量精度较低，无法估计贝壳与 14C 共存的日期。继该结果之后，利用记录了死亡日期的贝壳来估计贝壳生存的水生环境的新试验。这项试验的一个问题是，外壳会溶解在水和海水中，因此幼鱼的生长线通常会消失。另一个问题是，我们的研究中没有发现之前研究中报告的每日生长线。短颈蟹的壳被发现每天有两条或更多条生长线。测量的生长线距离似乎与风暴等海况有关，因此贝壳生长线的可用性很有可能。进一步的研究工作将有针对性地阐明贝壳生长线的产生机制并确定贝壳的死亡年份。

The purpose of this study was to put estimation of aquatic environment such as anoxia in the past in terms of growth line in shells within the bounds of possibility. Estimation of the date that a shell had been living with 14C was impossible in spite of the initial plan because of low accuracy of the measurements of 14C. This result was followed by a new trial on estimation of aquatic environment that a shell lived by using a shell of which the death date was recorded. One problem through this trial is that the outer-shell dissolves in water and seawater so that growth lines in juvenile have usually disappeared. The other problem is that daily growth lines reported in previous research were not found in our study. The shell of short neck crab was found to have two or more growth lines per day. Measured growth line distances seem to have a relationship with sea conditions such as storm therefore availability of growth lines of shells is highly possible. Further research work is to be targeted to elucidate the generation mechanism of growth lines of shells and to confirm the year of death of shells.