Volume, Heat, and Freshwater Divergences in the Subpolar North Atlantic Suggest the Nordic Seas as Key to the State of the Meridional Overturning Circulation
Volume, Heat, and Freshwater Divergences in the Subpolar North Atlantic Suggest the Nordic Seas as Key to the State of the Meridional Overturning Circulation
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DOI：
10.1029/2019gl082110
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发表时间：
2019-05-16
影响因子：
5.2
通讯作者：
Rossby, T.
中科院分区：
文献类型：
--
作者：
Chafik, Leon;Rossby, T.
在副极地和北欧地区，经向翻转环流（MOC）迅速减少，温暖的上层由于强烈的热量损失而失去浮力，下沉并向南流动。 MOC 上肢的主要体积损失，类似于 18.4 +/- 3.4 Sv 中的 9.6 Sv，发生在冰岛盆地和伊尔明格海的俯冲过程中，而主要的热量损失（395 +/- 74 TW 中的 273 TW）与 MOC 分支有关，该分支继续进入北欧海，产生北大西洋深溢流水。副极地环流中的 122 +/- 79 TW 热通量收敛似乎明显大于对大气热损失的各种估计。 0.09 +/- 0.02 Sv 的淡水分歧大部分可能是由格陵兰陆架的径流平衡的。这些估计表明，北欧海，而不是拉布拉多海，是 MOC 状态的关键。 简单语言摘要 经向翻转环流是上层海洋暖水向北流动及其作为冷的深水和中水向南返回的二维视图。但暖冷转换的实际路径有多种，而且非常多样化：一个分支继续进入北欧海，在那里产生非常稠密的水，并最终溢出到北大西洋深处；另一个分支绕过整个副极地盆地和格陵兰岛南端，到达形成中间水的拉布拉多海；第三个分支是在格陵兰岛和苏格兰之间的副极地水域内发生的翻转。从体积上来说，这是最大的分支，但就北欧海洋的热量损失而言，分支向大气传递的热量远多于其他两个分支的总和。因此，它对于维持强大的经向翻转环流起着关键作用。
The meridional overturning circulation (MOC) decreases rapidly in subpolar and Nordic regions where the warm upper layer loses its buoyancy due to intense heat loss, sinks, and flows south. The major volume loss of the upper limb of the MOC, similar to 9.6 Sv out of 18.4 +/- 3.4 Sv, occurs as subduction across the Iceland Basin and Irminger Sea while the major heat loss, 273 TW out of 395 +/- 74 TW is associated with the MOC branch that continues into the Nordic Seas where North Atlantic deep overflow water is produced. The 122 +/- 79 TW heat flux convergence in the subpolar gyre appears to be significantly larger than various estimates of heat loss to the atmosphere. Much of the 0.09 +/- 0.02 Sv freshwater divergence is presumably balanced by runoff from the Greenland shelf. These estimates suggest that the Nordic Seas, not the Labrador Sea, are key to the state of the MOC.Plain language summary The meridional overturning circulation is a two-dimensional view of the flow north of upper-ocean warm water and its return south as cold deep and intermediate water. But the actual pathways of warm-to-cold conversion are several and remarkably diverse: One branch continues into the Nordic Seas where very dense water is produced and eventually spills back into the deep North Atlantic, another branch weaves its way around the entire subpolar basin and the southern tip of Greenland to the Labrador Sea where intermediate water is formed, and the third branch is an overturning that takes place within the subpolar waters between Greenland and Scotland. Volumetrically, this is the largest branch, but in terms of heat loss the Nordic Seas, branch surrenders far more heat to the atmosphere than the other two combined. It thus plays the key role in maintaining a strong meridional overturning circulation.