The role of ocean gateways in the dynamics and sensitivity to wind stress of the early Antarctic Circumpolar Current
The role of ocean gateways in the dynamics and sensitivity to wind stress of the early Antarctic Circumpolar Current
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DOI：
10.1002/2014pa002675
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发表时间：
2015-03
期刊：
影响因子：
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通讯作者：
D. Munday;H. Johnson;D. Marshall
中科院分区：
文献类型：
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作者：
D. Munday;H. Johnson;D. Marshall
由于德雷克海峡和塔斯曼海道相对开放时间的不确定性，南极绕极流形成的日期存在争议。利用一个理想化的可解析涡旋的数值海洋模型，我们研究是否两个海洋通道都必须开放才能形成显著的绕极流。我们发现，只要能在障碍物周围找到一条绕极路径，重叠的大陆障碍物并不会阻碍超过50 Sverdrup（Sv）的绕极输送。然而，重叠障碍物的存在确实导致洋流体积输送对风应力变化的敏感性增加。这种敏感性的变化是根据大陆障碍物和水下地形的压力降在平衡表面风应力输入的动量方面所起的作用来解释的。具体而言，当跨大陆的压力降是动量的主要平衡汇时，纬向体积输送对风应力变化敏感。纬向体积输送的变化是通过改变绕极输送中与深度无关的部分而不是热成风切变引起的部分发生的。在这种情况下，等密度面在模型南大洋中继续陡峭倾斜，这意味着深海和表层海洋之间存在紧密联系。这可能会对经向翻转环流及其对风应力的敏感性产生影响。
The date of inception of the Antarctic Circumpolar Current is debated due to uncertainty in the relative opening times of Drake Passage and the Tasman Seaway. Using an idealized eddy-resolving numerical ocean model, we investigate whether both ocean gateways have to be open to allow for a substantial circumpolar current. We find that overlapping continental barriers do not impede a circumpolar transport in excess of 50Sv, as long as a circumpolar path can be traced around the barriers. However, the presence of overlapping barriers does lead to an increased sensitivity of the current's volume transport to changes in wind stress. This change in sensitivity is interpreted in terms of the role of pressure drops across continental barriers and submerged bathymetry in balancing the momentum input by the surface wind stress. Specifically, when the pressure drop across continents is the main balancing sink of momentum, the zonal volume transport is sensitive to changes in wind stress. Changes in zonal volume transport take place via altering the depth-independent part of the circumpolar transport rather than that arising from thermal wind shear. In such a scenario, isopycnals continue to slope steeply across the model Southern Ocean, implying a strong connection between the deep and surface oceans. This may have consequences for the meridional overturning circulation and its sensitivity to wind stress.