Atmospheric Δ14C reduction in simulations of Atlantic overturning circulation shutdown
Atmospheric Δ14C reduction in simulations of Atlantic overturning circulation shutdown
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DOI：
10.1002/gbc.20035
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发表时间：
2013-06
影响因子：
5.2
通讯作者：
Katsumi Matsumoto;Y. Yokoyama
中科院分区：
文献类型：
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作者：
Katsumi Matsumoto;Y. Yokoyama
大西洋纬向翻转环流（AMOC）的迅速减少可以显著地破坏全球热量输送，并可能引发末次冰期气候的突然变化。长期以来，人们一直认为AMOC的减缓会抑制大气和深海之间的碳交换，从而导致大气中产生的放射性碳（14 C）在大气中积累。事实上，先前的模型研究已经证明，AMOC的减少导致大气14 C丰度（Δ 14 C）升高。然而，这似乎不符合在海因里希1号和新仙女木stadial事件期间观察到的大气pCO2上升，以及新出现的观点，即这种CO2上升是由深海排放的“旧”碳造成的。使用地球系统模型，我们提供了一个替代方案，AMOC减速和伴随的动力学响应在南部（即，双极跷跷板）实际上会导致大气Δ 14 C的下降。当两极跷跷板和来自南大洋的旧碳通量足够大，以克服14C在大气中的积累，因为AMOC减少时，这种下降在模型中得以实现。我们描述的两极跷跷板引起了海洋遥相关，北大西洋的淡水扰动驱动了南部的Δ 14 C响应，但这并不一定排除大气遥相关。
A rapid reduction in the Atlantic meridional overturning circulation (AMOC) can significantly disrupt the global heat transport and likely triggered abrupt climate change during the last glacial cycle. A slowdown in AMOC has long been assumed to inhibit the exchange of carbon between the atmosphere and the deep ocean and thus cause radiocarbon (14C), which is produced in the atmosphere, to accumulate in the atmosphere. Indeed previous model studies have demonstrated that a reduction in AMOC leads to higher atmospheric 14C abundance (Δ14C). However, this seems inconsistent with the observed rise in atmospheric pCO2 during Heinrich 1 and the Younger Dryas stadial events and the emerging view that this CO2 rise resulted from the deep ocean venting “old” carbon. Using an Earth system model, we offer an alternative scenario that AMOC slowdown and an accompanying dynamical response in the south (i.e., the bipolar seesaw) can in fact lead to a decline in atmospheric Δ14C. This decline is realized in the model when the bipolar seesaw and thus the flux of old carbon from the Southern Ocean are sufficiently large so as to overcome the accumulation of 14C in the atmosphere as AMOC is reduced. The bipolar seesaw we describe invokes an oceanic teleconnection, whereby a freshwater perturbation in the North Atlantic drives a southern Δ14C response, but this does not necessarily preclude an atmospheric teleconnection.