Temporal variability in bottom water structures has been observed in 37-h high-resolution temperature data at the ocean bottom up to 67.4 m on the continental shelf of the northern South China Sea. The water temperature is generally hot (cold) in the downslope (upslope) flow, but rapid temperature change is associated with the cross-slope flow intensity changes. Downslope, wandering, and upslope phases are classified depending on the flow directions. Ellison scale method is used to evaluate the turbulent mixing. Intensive dissipation is observed in the wandering phase, the vertically integrated dissipation E_ɛ ∼ 322 mW/m² and the eddy diffusivity 〈K_z〉 in 0.01–0.15 m²/s, which is attributed to the critical interaction between the semidiurnal tides and the slope boundary. E_ɛ is gradually reduced to 38.1 mW/m² in the upslope phase, in which the topography is subcritical to the internal tides, while 〈K_z〉 is occasionally promoted to 0.077 m²/s owing to the weaker stratification. The bottom mixed layer is persistently exhibited, but highly intermittent around 13.9 m and varies from 0.2 m to greater than 67.4 m. Its thickness depends strongly on the water stratification and seems not to be directly linked with the turbulent mixing. The bottom unstable layer occurs mainly in the period slightly before and in the first half of the upslope flow phase. The induced convection makes a substantial contribution to the turbulent mixing when the overall mixing is relatively mild. In the intense mixing, even though the convectively driven mixing becomes much stronger, its contribution is less significant.

中文翻译：

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南海北部大陆坡底水结构的时间变化

在南海北部大陆架 67.4 m 海底的 37 小时高分辨率温度数据中观察到底水结构的时间变化。下坡（上坡）流水温一般为热（冷）温，但温度的快速变化与跨坡流强度变化有关。下坡、漂移和上坡阶段根据流向进行分类。埃里森标度法用于评估湍流混合。在漂移阶段观察到强耗散，垂直积分耗散E _ɛ ∼ 322 mW/ m ²和涡扩散系数 < K _z > 在 0.01–0.15 m ² / s，这归因于半日潮汐和斜坡边界之间的临界相互作用。E _ɛ在上升阶段逐渐降低到 38.1 mW/ m ²，其中地形对内部潮汐来说是次临界的，而 < K _z > 偶尔提升到 0.077 m ² / s由于分层较弱。底部混合层持续出现，但在 13.9 m 附近高度间歇，从 0.2 m 到大于 67.4 m 不等。它的厚度在很大程度上取决于水的分层，似乎与湍流混合没有直接关系。底部不稳定层主要发生在上坡流相的前半段和前半段。当整体混合相对温和时，诱导对流对湍流混合有很大贡献。在强烈混合中，即使对流驱动的混合变得更强，其贡献也不那么显着。