Enhanced weathering and CO2 drawdown caused by latest Eocene strengthening of the Atlantic meridional overturning circulation
Enhanced weathering and CO2 drawdown caused by latest Eocene strengthening of the Atlantic meridional overturning circulation
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DOI：
10.1038/ngeo2888
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发表时间：
2017-03-01
影响因子：
18.3
通讯作者：
Yang, Simon
中科院分区：
文献类型：
--
作者：
Elsworth, Genevieve;Galbraith, Eric;Yang, Simon
在明显大于105年的时间尺度上，大气p（CO2）是由地幔脱气速率相对于硅酸盐风化反馈的设定点控制的。风化设定点已被证明取决于暴露在地球表面的岩石的分布和特性、植被类型和地形。在这里，我们认为，海洋环流变化引起的大规模气候影响也可以改变风化设定点，并有证据表明这在始新世-渐新世边界南极冰盖的建立中发挥了作用。在我们的模拟中，德雷克海峡的构造加深导致南大洋的清新和分层，加强大西洋纬向翻转环流，从而提高温度，加强陆地上的降雨。这些模拟的变化是一致的始新世晚期构造重建，显示德雷克通道加深，并与沉积物记录，揭示南大洋分层，北大西洋深水的出现，和半球不对称的温度变化。这些因素可能会导致硅酸盐风化加剧，从而可以解释与南极冰盖生长有关的二氧化碳减少。我们认为，这种机制说明了另一种方式，海洋-大气气候动力学可以通过与地质碳循环的相互作用引入非线性阈值行为。
On timescales significantly greater than 105 years, atmospheric p(CO2) is controlled by the rate of mantle outgassing relative to the set-point of the silicate weathering feedback. The weathering set-point has been shown to depend on the distribution and characteristics of rocks exposed at the Earth's surface, vegetation types and topography. Here we argue that large-scale climate impacts caused by changes in ocean circulation can also modify the weathering set-point and show evidence suggesting that this played a role in the establishment of the Antarctic ice sheet at the Eocene-Oligocene boundary. In our simulations, tectonic deepening of the Drake Passage causes freshening and stratification of the Southern Ocean, strengthening the Atlantic meridional overturning circulation and consequently raising temperatures and intensifying rainfall over land. These simulated changes are consistent with late Eocene tectonic reconstructions that show Drake Passage deepening, and with sediment records that reveal Southern Ocean stratification, the emergence of North Atlantic Deep Water, and a hemispherically asymmetric temperature change. These factors would have driven intensified silicate weathering and can thereby explain the drawdown of carbon dioxide that has been linked with Antarctic ice sheet growth. We suggest that this mechanism illustrates another way in which ocean-atmosphere climate dynamics can introduce nonlinear threshold behaviour through interaction with the geologic carbon cycle.