Isopycnal mixing suppression by the Antarctic Circumpolar Current and the Southern Ocean Meridional Overturning Circulation

The meridional overturning circulation (MOC) in the Southern Ocean is investigated using hydrographic observations combined with satellite measurements of sea surface height. A three-dimensional (spatial and vertical) estimate of the isopycnal eddy diffusivity in the Southern Ocean is obtained using the theory of Ferrari and Nikurashin that includes the influence of suppression of the diffusivity by the strong, time-mean flows. It is found that the eddy diffusivity is enhanced at depth, reaching a maximum at the critical layer near 1000 m. The estimate of diffusivity is used with a simple diffusive parameterization to estimate the meridional eddy volume flux. This estimate of eddy volume flux is combined with an estimate of the Ekman transport to reconstruct the time-mean overturning circulation. By comparing the reconstruction with, and without, suppression of the eddy diffusivity by the mean flow, the influence of the suppression on the overturning is illuminated. It is shown that the...

本研究借助水文观测与卫星海面高度测量数据，对南大洋经向翻转环流（meridional overturning circulation, MOC）展开研究。基于Ferrari与Nikurashin提出的理论，研究人员获取了南大洋等密面涡动扩散率的三维（空间与垂向）估算结果，该理论纳入了强时间平均流对扩散率的抑制效应。研究发现，涡动扩散率在深层得到增强，在约1000米处的临界层达到峰值。将该扩散率估算结果与简单扩散参数化方案相结合，可估算经向涡动体积通量。将该涡动体积通量估算结果与埃克曼输运估算结果结合，即可重建时间平均翻转环流。通过对比考虑与不考虑平均流对涡动扩散率抑制作用的两种重建结果，阐明了该抑制效应对翻转环流的影响。研究表明，……