An abyssal carbonate compensation depth overshoot in the aftermath of the Palaeocene-Eocene thermal maximum
An abyssal carbonate compensation depth overshoot in the aftermath of the Palaeocene-Eocene thermal maximum
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DOI：
10.1038/ngeo2757
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发表时间：
2016-08
影响因子：
18.3
通讯作者：
D. Penman;S. Turner;P. Sexton;R. Norris;A. Dickson;S. Boulila;A. Ridgwell;R. Zeebe;J. Zachos;A. Cameron;T. Westerhold;U. Röhl
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文献类型：
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作者：
D. Penman;S. Turner;P. Sexton;R. Norris;A. Dickson;S. Boulila;A. Ridgwell;R. Zeebe;J. Zachos;A. Cameron;T. Westerhold;U. Röhl
在大约5600万年前的古新世-始新世热盛期（PETM）期间，数千千兆克的碳在短短几千年内被释放到大气和海洋中，随后在大约20万年内逐渐封存。如果硅酸盐风化是去除这种碳的关键负反馈之一，那么在事件的恢复阶段，预计海水碳酸钙饱和度将超过事件前的水平。在海洋沉积物中，这应被记录为一个暂时的深度加深，在此深度以下没有方解石被保存-方解石补偿深度（CCD）。在前PETM CCD之上的站点的先前和新的沉积记录显示PETM之后碳酸盐累积增强。来自北大西洋一个位于PETM前CCD之下的深海遗址的新记录显示，在PETM开始后约7万年开始的碳酸盐保存期，为CCD过度加深提供了第一个直接证据。这一记录证实了在PETM恢复期间海洋碳酸盐饱和度的超调。两个地球系统模型的模拟支持PETM的情景，涉及大量的初始碳释放，随后是长期的低水平排放，与CCD加深在我们的记录的时间一致。我们的研究结果表明，这些碳排放的封存是最有可能的结果，全球增强方解石埋藏以上的CCD和，至少在北大西洋，CCD的过度深化。
During the Palaeocene–Eocene Thermal Maximum (PETM) about 56 million years ago, thousands of petagrams of carbon were released into the atmosphere and ocean in just a few thousand years, followed by gradual sequestration over approximately 200,000 years. If silicate weathering is one of the key negative feedbacks that removed this carbon, a period of seawater calcium carbonate saturation greater than pre-event levels would be expected during the event's recovery phase. In marine sediments, this should be recorded as a temporary deepening of the depth below which no calcite is preserved — the calcite compensation depth (CCD). Previous and new sedimentary records from sites that were above the pre-PETM CCD show enhanced carbonate accumulation following the PETM. A new record from an abyssal site in the North Atlantic that lay below the pre-PETM CCD shows a period of carbonate preservation beginning about 70,000 years after the onset of the PETM, providing the first direct evidence for an over-deepening of the CCD. This record confirms an overshoot in ocean carbonate saturation during the PETM recovery. Simulations with two earth system models support scenarios for the PETM that involve a large initial carbon release followed by prolonged low-level emissions, consistent with the timing of CCD deepening in our record. Our findings indicate that sequestration of these carbon emissions was most likely the result of both globally enhanced calcite burial above the CCD and, at least in the North Atlantic, an over-deepening of the CCD.