Transient and Equilibrium Responses of the Atlantic Overturning Circulation to Warming in Coupled Climate Models: The Role of Temperature and Salinity
Transient and Equilibrium Responses of the Atlantic Overturning Circulation to Warming in Coupled Climate Models: The Role of Temperature and Salinity
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DOI：
10.1175/jcli-d-21-0912.1
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发表时间：
2022-08-01
影响因子：
4.9
通讯作者：
Rugenstein, Maria
中科院分区：
文献类型：
--
作者：
Bonan, David B.;Thompson, Andrew F.;Rugenstein, Maria
大西洋纬向翻转环流（AMOC）对气候变化的长期响应仍然知之甚少，部分原因是与运行大气-海洋环流模式（GCM）平衡相关的计算费用。在这里，我们使用的千年长度的GCM模拟的集合来检查的瞬态和平衡的AMOC的大气二氧化碳突然翻两番的反应。我们发现，GCM一贯模拟的AMOC减弱在第一世纪，但表现出不同的行为在较长的时间尺度，表现出不同的恢复水平。为了解释AMOC的行为，我们使用热风表达式，它将翻转环流与深水形成区和大西洋盆地之间的纬向密度差联系起来。使用这个表达式，我们属性的AMOC在不同的时间尺度上的温度和盐度的变化，在不同的区域的演变。最初的AMOC变浅和减弱发生在百年的时间尺度上，并归因于深水形成区域的变暖。在接下来的几个世纪中，AMOC会部分恢复，这与大西洋盆地的同时变暖和高纬度盐度的正异常有关。后者减少了地下分层，使深水地层重新活跃起来。表现出长期AMOC减弱的GCM往往具有较小的高纬度盐度异常和增加的北极海冰损失。几千年后，由于低纬度大西洋的变暖，一些GCM中的AMOC比初始状态更强。这些结果强调了在长时间尺度上研究AMOC演变的过去和未来演变时考虑高纬度淡水变化的重要性。海洋全球翻转环流对变暖的长期反应仍然知之甚少，主要是因为运行最先进的气候模型成本高昂。这项研究利用了来自不同气候模式的千年气候模拟的独特集合，以研究大西洋翻转环流对长时间尺度变暖的响应。我们发现，气候模式一致模拟大西洋翻转环流在变暖后的第一个世纪减弱，但不同意长期的变化，表现出不同的恢复水平的大西洋翻转环流。使用一个简单的表达式，它模拟气候模型中的大西洋翻转环流的演变，我们表明，气候模型几乎没有恢复往往有一个小的北大西洋盐度异常，而气候模型具有较强的恢复往往有一个大的北大西洋盐度异常。这些结果突出了监测高纬度淡水资源在整个二十一世纪的重要性，并考虑到温度和盐度变化的相对作用时，审查未来和过去的演变大西洋翻转环流的长时间尺度。
The long-term response of the Atlantic meridional overturning circulation (AMOC) to climate change remains poorly understood, in part due to the computational expense associated with running atmosphere-ocean general circulation models (GCMs) to equilibrium. Here, we use a collection of millennial-length GCM simulations to examine the transient and equilibrium responses of the AMOC to an abrupt quadrupling of atmospheric carbon dioxide. We find that GCMs consistently simulate an AMOC weakening during the first century but exhibit diverse behaviors over longer time scales, showing different recovery levels. To explain the AMOC behavior, we use a thermal-wind expression, which links the overturning circulation to the meridional density difference between deep-water formation regions and the Atlantic basin. Using this expression, we attribute the evolution of the AMOC on different time scales to changes in temperature and salinity in distinct regions. The initial AMOC shoaling and weakening occurs on centennial time scales and is attributed to a warming of the deep-water formation region. A partial recovery of the AMOC occurs over the next few centuries, and is linked to a simultaneous warming of the Atlantic basin and a positive high-latitude salinity anomaly. The latter reduces the subsurface stratification and reinvigorates deep-water formation. GCMs that exhibit a prolonged AMOC weakening tend to have smaller high-latitude salinity anomalies and increased Arctic sea ice loss. After multiple millennia, the AMOC in some GCMs is stronger than the initial state due to warming of the low-latitude Atlantic. These results highlight the importance of considering high-latitude freshwater changes when examining the past and future evolution of the AMOC evolution on long time scales. Significance StatementThe long-term response of the ocean's global overturning circulation to warming remains poorly understood largely because it is expensive to run state-of-the-art climate models. This study makes use of a unique collection of millennial-length climate simulations from different climate models to examine the response of the Atlantic overturning circulation to warming on long time scales. We find that climate models consistently simulate a weakening of the Atlantic overturning circulation during the first century after warming, but disagree on long-term changes, showing different recovery levels of the Atlantic overturning circulation. Using a simple expression, which emulates the evolution of the Atlantic overturning circulation in climate models, we show that climate models with little to no recovery tend to have a small North Atlantic salinity anomaly while climate models with a stronger recovery tend to have a large North Atlantic salinity anomaly. These results highlight the importance of monitoring high-latitude freshwater sources throughout the twenty-first century and considering the relative role of temperature and salinity changes when examining the future and past evolution of the Atlantic overturning circulation on long time scales.