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亜亜亜紀初期に海洋が拡大した窒素同位体証拠

Emma R Kast¹, Daniel A Stolper^2,3, Alexandra Auderset^4,5

¹Department of Geosciences, Princeton University, Princeton, NJ 08540, USA. ekast@princeton.edu.

Science (New York, N.Y.)

|April 27, 2019

まとめ

海洋の窒素循環の変動は,何百万年にもわたって不明である. 5700万年前より前の高い窒素同位体比 (δ15N) は,広範囲にわたるサブボクシアを示唆し,その後にアジアとインドの衝突に関連した減少が続いた.

科学分野:

古代海洋学
地化学
海の窒素循環

背景:

海の窒素循環の長期的変動はまだ十分に理解されていない.
フォラミニフェラの窒素同位体比 (δ15N) は,過去の海洋状態を再構築するための重要なプロキシである.

研究の目的:

海洋窒素循環の百万年の変動を調査する.
地質学的な時間尺度におけるサブボクシアとデニトリフィケーションの変化の原動力を理解する.

主な方法:

フォラミニフェラの殻に結合した有機物質の15N/14N比 (δ15N) の分析
過去の海洋状態を再現するために3つの堆積物を利用しました.

主要な成果:

5700万年前より前の高いδ15N値は,膨張した水柱のサブボキアと脱窒化を示しています.
地球温暖化以前の57~50万年間の δ15Nの減少は,おそらくテティス海の影響による,初期のアジア・インド衝突と一致した.
50~35 Maの低いδ15N値は,広範囲にわたる大陸棚の脱窒化を示唆している.
35万年後の δ15Nの上昇は,氷床の拡大,海平面の低下,大陸棚の縮小と相関している.

結論:

海洋の窒素循環は何百万年にもわたって構造変化や気候変動の影響で大きく変化してきました
アジアとインドの衝突やテティス海の進化などの海洋学と地質学的な要因は,窒素循環と海洋無酸素を調節する上で重要な役割を果たした.

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