Energetics of the abyssal ocean account greatly for the redistribution and dissipation of global oceanic energy. In this study, we characterize the intraseasonal fluctuations in the deep South China Sea (SCS) and evaluate the relevant energy budget using observations and numerical simulations. The results indicate substantial geographical inhomogeneity in the intraseasonal energy reservoir. The high-energy zones are located in the northwest of the Luzon Strait, northern slopes, deep western boundary current region, and southwestern cyclonic gyre region, where the intraseasonal fluctuations account for about 70% of the deep energy variability. Vorticity and divergence patterns of the intraseasonal motions are suggestive of quasigeostrophic dynamics, which are mostly attributed to the hybrid topographic–planetary Rossby waves. The flow field exhibits a weak lateral shear and appears to have symmetric instability with negative vorticity skewness, particularly over the sloping topography. Energetics analysis demonstrates that the intraseasonal fluctuations in the abyssal SCS obtain energy primarily from the upper layer through pressure work, while secondarily from advective transport and cross-scale transfer due to instability of the deep circulation. To reach equilibrium, the energy gained is mostly damped by dissipations. As another reference in the marginal sea with intensive mixing, our study highlights the potential universality in how the intraseasonal energy is fueled and dissipated in the abyss.

深海能量在很大程度上解释了全球海洋能量的重新分配和耗散。在这项研究中，我们描述了南海深处（SCS）的季节性波动，并使用观测和数值模拟评估了相关的能量收支。结果表明季节性内能源库存在很大的地理不均匀性。高能区位于吕宋海峡西北部、北坡、深西边界流区和西南气旋环流区，深部能量变率的70%左右是季节内波动。季节内运动的涡度和发散模式暗示了准地转动力学，这主要归因于混合的地形-行星罗斯贝波。流场表现出弱横向剪切，并且似乎具有负涡度偏度的对称不稳定性，特别是在倾斜地形上。能量学分析表明，深海南海的季节内波动主要通过压力功从上层获取能量，其次是由于深部环流的不稳定性，从平流输送和跨尺度转移获得能量。为了达到平衡，获得的能量主要被耗散所抑制。作为边缘海中强烈混合的另一个参考，我们的研究强调了季节内能量如何在深渊中被激发和消散的潜在普遍性。能量学分析表明，深海南海的季节内波动主要通过压力功从上层获取能量，其次是由于深部环流的不稳定性，从平流输送和跨尺度转移获得能量。为了达到平衡，获得的能量主要被耗散所抑制。作为边缘海中强烈混合的另一个参考，我们的研究强调了季节内能量如何在深渊中被激发和消散的潜在普遍性。能量学分析表明，深海南海的季节内波动主要通过压力功从上层获取能量，其次是由于深部环流的不稳定性，从平流输送和跨尺度转移获得能量。为了达到平衡，获得的能量主要被耗散所抑制。作为边缘海中强烈混合的另一个参考，我们的研究强调了季节内能量如何在深渊中被激发和消散的潜在普遍性。