The warming and salinification of the northwards flowing water masses from the Southern Ocean to the tropics are studied with Lagrangian trajectories simulated using fields from an Earth System Model. The trajectories are used to trace the geographical distribution of the water mass transformation and connect it with the pathways of the upper limb of the overturning circulation in the Southern Hemisphere. In the Antarctic Circumpolar Current water gains heat just below the mixed layer, mainly when the layer is thin during Austral spring and summer. This gain is therefore suggested to be a consequence of heat flux from the atmosphere and mixing processes at the base of the mixed layer. In the Southern Hemispheric subtropical gyres on the other hand, a large warming and salinification of the northwards flowing water results from internal mixing with other warmer and more saline water masses. Close to the Antarctic shelf waters are getting fresher as a result of ice melting, whereas further north, in the Antarctic Circumpolar current, waters are getting more saline as a result of evaporation. Our results show that it is not only the heat and freshwater fluxes through the sea surface that control the heat and salt changes of the upper limb of the overturning circulation in the Southern Hemisphere. In fact, internal mixing accounts for 25% of the heat change, and 22% of the salinity change.

中文翻译：

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南半球翻转环流上肢水团的变化

使用来自地球系统模型的场模拟的拉格朗日轨迹研究了从南大洋向北流动的水团的变暖和盐化。这些轨迹用于追踪水团转换的地理分布，并将其与南半球翻转环流上肢的路径连接起来。在南极环极流中，水在混合层正下方获得热量，主要是在南方春季和夏季混合层很薄时。因此，这种增益被认为是来自大气的热通量和混合层底部的混合过程的结果。另一方面，在南半球副热带环流中，向北流动的水的大量变暖和盐化是由于与其他更温暖和更多咸水团的内部混合造成的。由于冰融化，靠近南极大陆架的水域变得更加新鲜，而在更北的南极环极流中，由于蒸发，水域变得更加咸。我们的研究结果表明，不仅是通过海面的热量和淡水通量控制了南半球翻转环流上肢的热量和盐分变化。事实上，内部混合占热量变化的 25%，盐度变化的 22%。由于蒸发，水变得越来越咸。我们的研究结果表明，不仅是通过海面的热量和淡水通量控制了南半球翻转环流上肢的热量和盐分变化。事实上，内部混合占热量变化的 25%，盐度变化的 22%。由于蒸发，水变得越来越咸。我们的研究结果表明，不仅是通过海面的热量和淡水通量控制了南半球翻转环流上肢的热量和盐分变化。事实上，内部混合占热量变化的 25%，盐度变化的 22%。