2017 Fiscal Year Research-status Report
初期地球の海水量とその進化: 酸素・水素同位体分析法の開発と解析
| Project/Area Number |
16K05619
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
フォリエル ジュリアン 東京工業大学, 地球生命研究所, 特任助教 (60747161)
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| Project Period (FY) |
2016-04-01 – 2019-03-31
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| Keywords | oxygen isotopes / hydrogen isotopes / analytical development / water cycle / Archaean environment |
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| Outline of Annual Research Achievements |
During FY2017, I finalized the protocol for silicate δ18O microfluorination analysis. Inter-laboratory standards have been acquired and data acquisition is ongoing. A critical step in sample preparation protocol (mixing of bulk sample with fluorine and carbon reagents before preparation of individual replicates) was established this year which leads to better long term reproducibility of the data. The value of seawater δ18O is critical to constrain surface temperature but very poorly constrained until now. The first series of measurements on Archaean seawater-altered rocks argue for a seawater for δ18O similar to the modern. This needs to be confirmed on larger sample sets. My results so far argue for a near constant seawater δ18O since the Archaean.
At the same time, we (with collaborators including Kurokawa Hiroyuki) finalized a model for the evolution of H isotopes during water cycling. This model suggests that hydrogen escape, net regassing (more water subducted than degassed) or faster plate tectonics are necessary to explain the evolution of seawater H isotope composition. In either case, the modeling suggest a larger ocean volume in the Archean. This corresponds to a smaller emerged land surface and lower nutrient input into the ocean which could have important consequences for Earth habitability and the size of the biosphere. A paper is in review with EPSL.
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| Current Status of Research Progress |
Current Status of Research Progress
3: Progress in research has been slightly delayed.
Reason
Access to instrument (mMAT253 mass spectrometer) was difficult in FY2016 (about 6 months off for repairs) and FY2017 (about 5 months off for instrument modification). Therefore analytical part of project is a bit late. Modeling part is going well.
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| Strategy for Future Research Activity |
In the last year of the Kiban C project:
- accumulate δ18O data for Archaean seawater composition
- synthetize H isotope data and apply to the water cycle model we have to understand the volume of the ocean between 4 and 2.5 Ga
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| Causes of Carryover |
Because of some experimental delays (instrument not available) I did not yet setup automation of the microfluorination experiment and I did not used all FY2017 budget for this reason. The budget will be used this year for purchase of switching valves and other parts.
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