| 研究課題/領域番号 |
16K05571
|
|---|
| 研究機関 | 秋田大学 |
|---|
研究代表者 |
|
|---|
| 研究分担者 |
横山 祐典 東京大学, 大気海洋研究所, 教授 (10359648)
|
|---|
| 研究期間 (年度) |
2016-04-01 – 2019-03-31
|
| キーワード | stratigraphy / age modelling / eruption history / precipitation history |
|---|
| 研究実績の概要 |
A large number of additional radiocarbon dates have been added to the Lake Motosu record to further refine the age model. Several of these were performed on bulk organic matter from the same stratigraphic level as two tephras. This allowed the well-constrained calendar ages of the eruptions to be reversed calibrated to radiocarbon years for the purpose of determining variability in the reservoir age of the lake. The radiocarbon age of the surface water of the lake was also determined. Together this results in excellent agreement between the bulk organic dates, which are subject to increased uncertainty, with the radiocarbon dates obtained from terrestrial macrofossils. All of this information has been combined into a newly-developed, state of the art, deterministic age model. The model is being widely applied to other locations, and at present is used in a number of manuscripts.
Using this age model, we have greatly refined the ages of two Mt. Fuji eruptions from the Subashiri-C Stage. This has implications for the timing of the eruption and the dispersal patter of ejecta. We have also identified two eruptions that appear to be previously undetected. These occurred in quick succession, and would likely appear as a single larger eruption in a land-based, trench survey due to the lack of time for soil development.
Work has started for conducting oxygen isotope analyses of materials obtained from the lake. In the proces of sampling we identified >10 additional terrestrial macrofossils for age dating. This will further refine the chronology of the record.
|
| 現在までの達成度 (区分) |
現在までの達成度 (区分)
1: 当初の計画以上に進展している
理由
The aggressive campaign of high-density radiocarbon dating has returned excellent results that formed the basis for development of a new, deterministic age model that provides more realistic estimates of uncertainty that previously available models. The applicability of this model is wider than initially expected, and it has been already successfully used to model ages in highly disturbed coral sections. We have also determined that cellulose in the lake organic matter is primarily of aquatic origin. This makes cellulose also a viable target for oxygen isotope precipitation reconstruction. Combined with oxygen isotopes of diatom silica, this could provide a paleothermometer for reconstructing changing lake surface temperature. This is an exciting prospect beyond initial expectatioins.
|
| 今後の研究の推進方策 |
Radiocarbon of additional macrofossils will be performed. Monthly sampling of the lake surface water for determining it's baseline oxygen isotope signal and variability will be performed. Oxygen isotope analysis of aquatic cellulose is underway for a monsoon reconstruction. The viability of a temperature reconstruction based on combined cellulose and silica data will be explored.
|
| 次年度使用額が生じた理由 |
The oxygen isotope analyses were delayed. These are being performed this year. The samples have been taken and are currently being processed.
|
