Model sensitivity of the Weddell and Ross seas, Antarctica, to vertical mixing and freshwater forcing
Model sensitivity of the Weddell and Ross seas, Antarctica, to vertical mixing and freshwater forcing
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DOI：
10.1016/j.ocemod.2015.08.003
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发表时间：
2015-10
期刊：
影响因子：
3.2
通讯作者：
J. Kjellsson;P. Holland;G. Marshall;P. Mathiot;Y. Aksenov;A. Coward;S. Bacon;A. Megann;J. Ridley
中科院分区：
文献类型：
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作者：
J. Kjellsson;P. Holland;G. Marshall;P. Mathiot;Y. Aksenov;A. Coward;S. Bacon;A. Megann;J. Ridley
我们使用海洋-海冰模式研究了韦德尔海和罗斯海对垂直混合和表层淡水强迫的敏感性。高纬度南大洋是非常弱的层结，整个跃层的冬季盐度差只有∼0.2PSU。我们发现，垂直混合不足、来自南极冰盖的淡水供应或初始海冰导致混合层中盐度偏高，从而侵蚀了层结，并导致了过度的深部对流。这导致了韦德尔海和罗斯海的垂直均质化，海冰中的冰川开放，亚极圈和南极绕极流不切实际的旋转。模型中的淡水收支表明，∼的任何一个分量只要有30%的误差，就可以在大约十年内使海洋分层。我们发现，模式中的淡水强迫在南极海岸线上应该是足够的，以平衡由于密集的海岸水不能沉入深海而引起的盐度偏差。我们还表明，低初始海冰面积在边缘冰区引入了盐度偏差。我们论证了需要同时约束垂直混合、淡水强迫和初始海冰条件，才能在模式中再现南大洋水文、环流和海冰。例如，垂直混合不足将导致韦德尔海和罗斯海的过度对流，即使在存在大的表层淡水强迫和初始海冰覆盖的情况下。
We examine the sensitivity of the Weddell and Ross seas to vertical mixing and surface freshwater forcing using an ocean–sea ice model. The high latitude Southern Ocean is very weakly stratified, with a winter salinity difference across the pycnocline of only ∼0.2 PSU. We find that insufficient vertical mixing, freshwater supply from the Antarctic Ice Sheet, or initial sea ice causes a high salinity bias in the mixed layer which erodes the stratification and causes excessive deep convection. This leads to vertical homogenisation of the Weddell and Ross seas, opening of polynyas in the sea ice and unrealistic spin-up of the subpolar gyres and Antarctic Circumpolar Current. The model freshwater budget shows that a ∼30% error in any component can destratify the ocean in about a decade. We find that freshwater forcing in the model should be sufficient along the Antarctic coastline to balance a salinity bias caused by dense coastal water that is unable to sink to the deep ocean. We also show that a low initial sea ice area introduces a salinity bias in the marginal ice zone. We demonstrate that vertical mixing, freshwater forcing and initial sea ice conditions need to be constrained simultaneously to reproduce the Southern Ocean hydrography, circulation and sea ice in a model. As an example, insufficient vertical mixing will cause excessive convection in the Weddell and Ross seas even in the presence of large surface freshwater forcing and initial sea ice cover.