エルニーニョによって引き起こされる大気中のCO2の酸素同位体の年間変動
Lisa R Welp1, Ralph F Keeling, Harro A J Meijer
1Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093-0244, USA. lwelp@ucsd.edu
Nature
|September 30, 2011
まとめ
大気中の二酸化炭素 (CO2) の安定した同位体比は,エルニニョ/南方振動との強い関連性を明らかにしています. この連結は,植物と海洋による地球規模の炭素吸収の推定を精査するのに役立ち,これまで考えられていたよりも速いCO2循環を示唆しています.
科学分野:
- 大気化学と生地化学のサイクル.
- イソトープ地化学. イソトープ地化学.
- 気候科学と炭素循環への影響.
背景:
- 大気中のCO2の安定イソトープ比 ((18) O/(16) Oと (13) C/(12) C) は,世界の炭素循環を理解するために監視されています.
- CO(2) の酸素同位体変動の解釈は,炭素と水のサイクルの両方の影響により複雑である.
- 以前の研究では,1990年代に減少した (18) O/(16) O比率に焦点を当て,それを土壌呼吸,作物の変化,環境条件などの要因に起因した.
研究 の 目的:
- スクリップス海洋研究所 (Scripps Institution of Oceanography) のグローバルフラッシュネットワークから,大気中のCO2に関する30年間の (18) O/(16) Oデータを分析する.
- 大気中のCO2イソトープの年次変動と気候パターン,特にエルニーニョ/南方振動 (ENSO) の間の関係を調査する.
- ENSOに関連する同位体信号を使用して,世界の総原産 (GPP) の見積もりを制限する.
主な方法:
- 世界的なボトルサンプリングネットワークからの30年間の大気中のCO2 (18) O / 16) O比率のデータセットを使用.
- ENSOイベントと,熱帯降雨と植物水における関連する変化と,年間の同位体変動を相関させる.
- 同位体記録のENSO異常の崩壊時間を分析して,CO2のサイクル時間を推論する.
主要な成果:
- 大気中のCO2 (18) O/(16) O比率の年間変動とエルニーニョ/南方振動との間に強い相関が認められた.
- ENSOによる熱帯の水分再分配の変化は,降雨と植物の水の (18) O/(16) O比に影響を及ぼし,これは大気中のCO2に転送される.
- ENSOイベントからの観測された急速な回復は,生物圏,海洋,大気間のCO2サイクル時間が,以前に推定されたよりも短いことを示唆しています.
結論:
- エルニーニョ/南方振動は,水循環と生物圏と大気間の交換に及ぼす影響を通じて,大気中のCO2イソトープ組成に大きく影響を与える.
- 現在の世界原産総量 (GPP) の見積もりは過小評価されている可能性があり,150〜175 Pg C yrの修正されたGPPを提案しています.
- この改訂されたGPP推定値は,地球生物圏の炭素循環モデルを評価するための新しい基準を提供します.
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