2022 Fiscal Year Final Research Report
Appearance and evolution of C4 plants: Environmental perturbation around Antarctica during mid-Cretaceous
| Project/Area Number |
19H02011
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Review Section |
Basic Section 17050:Biogeosciences-related
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| Research Institution | Kanazawa University |
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Principal Investigator |
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| Co-Investigator(Kenkyū-buntansha) |
中村 英人 大阪公立大学, 大学院理学研究科, 特任講師 (00785123)
黒田 潤一郎 東京大学, 大気海洋研究所, 准教授 (10435836)
守屋 和佳 早稲田大学, 教育・総合科学学術院, 教授 (60447662)
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| Project Period (FY) |
2019-04-01 – 2022-03-31
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| Keywords | 白亜紀 / 炭素同位体比 / バイオマーカー / アルケノン / 海洋無酸素事変 / 二酸化炭素分圧 |
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| Outline of Final Research Achievements |
Initial purpose of this study was to elucidate paleoenvironments of southern high latitude based on compound-specific carbon isotope analysis on plant biomarkers expecting discovery of C4 plant evidence. Unfortunately, we couldn't find any of its carbon-isotopic evidence. On the other hand, we recognized significant biomarkers (alkenones) from haptophytes. It was first discovery of paired occurrence of di- and tri-unsatureated alkenones from Cretaceous sediments. As we realized that they could be a proxy for paleothermometry, we switched target compounds to alkenones and studied an Albian through lowest Turonian sequence. As a result, conjoined rapid drop of pCO2 and SST was decoded from the early stage of Oceanic Anoxic Evenbt 2. The cooling is interpreted to be comparable to Plenus Cold Event (PCE) known from the Northern Hemisphere. Our results indicate PCE was a global event associated with global pCO2 drop derived from major sequestration of organic carbon over extended sea floor.
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| Free Research Field |
古環境学
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| Academic Significance and Societal Importance of the Research Achievements |
世界で初めて白亜紀の３不飽和アルケノンを発見した．２不飽和と３不飽和アルケノンが同時検出されれば古水温指標となるため極めて重要である．２不飽和アルケノンは含有量が多く，かつその起源がハプト藻類と明確だが，その炭素同位体比(d13C)測定に成功した．これも白亜系では初である．酸性化により炭酸塩が失われる場合が多い深海の海洋無酸素事変２記録ではd13C層序指標の確認が困難だが，本研究で初めてアルケノンd13C層序を用いてこれを克服した．温暖化が極度に進んだ白亜紀においてパルス的CO2増加が強い負の炭素循環フィードバックを誘導し，その結果世界中の表層海水温が低下したことを実データで示すことができた．
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