Abrupt North Atlantic circulation changes in response to gradual CO2 forcing in a glacial climate state
Abrupt North Atlantic circulation changes in response to gradual CO2 forcing in a glacial climate state
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DOI：
10.1038/ngeo2974
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发表时间：
2017-07
影响因子：
18.3
通讯作者：
Xu Zhang;G. Knorr;G. Lohmann;S. Barker
中科院分区：
文献类型：
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作者：
Xu Zhang;G. Knorr;G. Lohmann;S. Barker
冰川气候的特点是突然的，千年尺度的气候变化被称为丹斯加德-奥施格周期。最明显的stadial冷却，海因里希事件，与大规模的冰山排放到北大西洋。这些事件与大西洋纬向翻转环流强度的变化有关。然而，导致强环流和弱环流之间突然转变的因素仍然不清楚。在这里，我们表明，在一个完全耦合的大气-海洋模式中，大气CO2浓度的逐渐变化可以触发气候突变，与大西洋纬向翻转环流在中间冰川条件下的双稳定性制度。我们发现，大气CO2浓度的变化改变了整个中美洲的大气水分的运输，从而调节北大西洋的淡水预算，因此深水形成。在我们的模拟中，大气中CO2水平的变化约为15 ppmv的变化在丹斯高-奥施格周期包含海因里希事件，足以导致弱stadial和强stadial间环流模式之间的过渡。由于大西洋纬向翻转环流的变化被认为会改变大气CO2水平，我们推断，大气CO2可能作为一个负反馈强，弱环流模式之间的转换。
Glacial climate is marked by abrupt, millennial-scale climate changes known as Dansgaard–Oeschger cycles. The most pronounced stadial coolings, Heinrich events, are associated with massive iceberg discharges to the North Atlantic. These events have been linked to variations in the strength of the Atlantic meridional overturning circulation. However, the factors that lead to abrupt transitions between strong and weak circulation regimes remain unclear. Here we show that, in a fully coupled atmosphere–ocean model, gradual changes in atmospheric CO2concentrations can trigger abrupt climate changes, associated with a regime of bi-stability of the Atlantic meridional overturning circulation under intermediate glacial conditions. We find that changes in atmospheric CO2concentrations alter the transport of atmospheric moisture across Central America, which modulates the freshwater budget of the North Atlantic and hence deep-water formation. In our simulations, a change in atmospheric CO2levels of about 15 ppmv—comparable to variations during Dansgaard–Oeschger cycles containing Heinrich events—is sufficient to cause transitions between a weak stadial and a strong interstadial circulation mode. Because changes in the Atlantic meridional overturning circulation are thought to alter atmospheric CO2levels, we infer that atmospheric CO2may serve as a negative feedback to transitions between strong and weak circulation modes.