Global carbon cycle perturbation across the Eocene-Oligocene climate transition
Global carbon cycle perturbation across the Eocene-Oligocene climate transition
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DOI：
10.1002/2015pa002818
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发表时间：
2016-02
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影响因子：
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通讯作者：
D. A. McKay;T. Tyrrell;P. Wilson
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作者：
D. A. McKay;T. Tyrrell;P. Wilson
始新世-渐新世转变(EOT)，约34 Ma，标志着新生代温室向冰库气候转变的一个转折点。古记录揭示了跨EOT的逐步快速冷却和冰的增长，与短暂的海底13℃漂移和碳酸盐补偿深度(Ccd)的主要和永久加深密切相关。基于生物地球化学盒模型，Merico等人。(2008)提出，(1)冰川隆起海平面下降导致陆架盆地碳酸盐埋藏分馏和(2)陆架碳酸盐风化可以解释碳循环扰动，但这一发现受到了质疑。提出的替代机制包括增加海洋通风，减少碳酸盐埋藏，增加有机碳埋藏，增加硅酸盐风化，以及增加海洋钙浓度。在这里，我们使用Merico等人的生物地球化学盒模型的改进版本。(2008)为了重新评估这些相互矛盾的假设和一个额外的机制，扩大“碳电容器”，如永久冻土和泥炭地。我们发现，钙浓度、硅酸盐风化和碳酸盐或有机碳埋藏的变化都产生了与古记录的形式和/或标志根本不一致的响应。陆架盆地碳酸盐埋藏分馏作用(Ccd变化)，加上陆架碳酸盐风化作用，富含12C的碳被封存到碳电容器中，以及可能增加的海洋通风(13C漂移)，提供了与古记录最匹配的结果。需要进一步的工作来理解为什么EOT碳循环扰动是如此独特，而假设的责任机制(冷却和冰增长)并不是这一事件所特有的。
The Eocene-Oligocene transition (EOT), ~34?Ma, marks a tipping point in the long-term Cenozoic greenhouse to icehouse climate transition. Paleorecords reveal stepwise rapid cooling and ice growth across the EOT tightly coupled to a transient benthic ?13C excursion and a major and permanent deepening of the carbonate compensation depth (CCD). Based on biogeochemical box modeling, Merico et al. (2008) suggested that a combination of (1) glacioeustatic sea level fall-induced shelf-basin carbonate burial fractionation and (2) shelf carbonate weathering can account for the carbon cycle perturbation, but this finding has been questioned. Alternative proposed mechanisms include increased ocean ventilation, decreased carbonate burial, increased organic carbon burial, increased silicate weathering, and increased ocean calcium concentration. Here we use an improved version of the biogeochemical box model of Merico et al. (2008) to reevaluate these competing hypotheses and an additional mechanism, the expansion of “carbon capacitors” such as permafrost and peatlands. We find that changes in calcium concentration, silicate weathering, and carbonate or organic carbon burial each yield a response that is fundamentally at odds with the form and/or sign of the paleorecords. Shelf-basin carbonate burial fractionation (CCD change), plus shelf carbonate weathering, sequestration of 12C-enriched carbon into carbon capacitors, and possibly increased ocean ventilation (?13C excursion), offers the best fit to the paleorecords. Further work is needed to understand why the EOT carbon cycle perturbation is so unique when the forcing mechanisms hypothesized to be responsible (cooling and ice growth) are not peculiar to this event.