氷河海における窒素固定の減少は,海洋の窒素とリンの在庫の変化から推測される
Raja S Ganeshram1, Thomas F Pedersen, Stephen Calvert
1Department of Geology and Geophysics, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, UK. Raja.Ganeshram@glg.ed.ac.uk
Nature
|January 24, 2002
まとめ
氷河期には,海洋の窒素とリンが増加したが,より高いN/P比は窒素固定を抑制し,海洋の生産性と二酸化炭素の吸収を増加させる鉄の肥料化仮説に疑問を呈した.
科学分野:
- パレオセアノグラフィー
- マリン・バイオジオケミストリー
- 気候科学 気候科学
背景:
- 氷河期における大気中の二酸化炭素の減少は,しばしば海洋植物プランクトンの生産性の増加によって説明される.
- 鉄の肥料化仮説によると,鉄粉が増えると窒素の固定が刺激され,植物プランクトンの成長とCO2の吸収が促進される.
研究 の 目的:
- 氷河期における海洋生産性の規制における栄養素の利用可能性と窒素固定の役割を調査する.
- 栄養素のダイナミクスを調べることによって,現存する鉄の肥料化仮説に異議を唱える.
主な方法:
- メキシコの北西の大陸の縁からの堆積物核の分析.
- 氷河期におけるデニトリフィケーションとフォスフォライト形成率の再構築.
主要な成果:
- 氷河期の間,デニトリフィケーションとリン酸塩の形成は減少し,海洋の窒素とリン酸の在庫が増えました.
- は窒素よりもゆっくりと増加し,N/P比が上昇した.
- 増加したN/P比は,鉄の肥料化仮説に反して,窒素固定を抑制した可能性がある.
結論:
- 氷河期における栄養素の在庫の増加や鉄の供給により,海洋の生産性は向上しなかった可能性が高い.
- 鉄刺激による窒素固定の提案されたメカニズムは,氷河におけるCO2濃度の低下を説明できないかもしれない.
- 海洋の栄養循環とN/P比は,海洋の生産性と炭素の吸収を規制する上で重要な役割を果たします.
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