Shallow seamounts are becoming increasingly recognised as key habitats for conservation due to their role as biological refuges, particularly throughout oligotrophic oceans. Traditionally, Taylor caps have been invoked as the mechanism driving biomass aggregation over seamounts but emerging evidence based on higher resolution measurements highlights the importance of internal waves (IW) to the local ecosystem. These waves can flush the benthic habitat with cool water from depth and impact on nutrient supply over short time scales through turbulent mixing that may also influence fish behaviour. They are dependent on the regional stratification, however, and thus influenced by planetary-scale variability in oceanographic conditions. We present here detailed observations of the internal wave regime over a shallow seamount, called Sandes, in the central Indian Ocean throughout different phases of the Indian Ocean Dipole (IOD) that modulated the regional stratification. A deep thermocline, caused by the 2019 IOD event precluded internal wave activity over the summit, whereas a thermocline collocated with the summit during 2020 when the IOD reversed polarity resulted in a 30 m amplitude internal tide signal (t ∼ 12.5 h). A shallow thermocline, observed during 2022, resulted in propagation of IWs over the summit with less visible internal tide. Harmonic analysis shows the presence of high frequency waves (t ∼ 15 min) on both flanks of the seamount during 2020 & 2022, which are likely a result of local shear instability, whereas 2019 shows an asymmetric response, potentially due to the strong background current and suppression of the thermocline beneath the depth of the summit. The potential importance of the waves over the summit to the local ecosystem may be attributed to the elevated turbulence measured at the thermocline during internal wave propagation, with ε > 10 W kg-1 routinely observed. Our results highlight the ability of thermocline depth to act as a gating condition for internal wave evolution over the summit. These results show that, whilst the water column exhibits variability at short spatiotemporal scales compared to the frequently cited Taylor cap dynamics, it is also regulated by the wider basin scale processes. Thus, a more integrated approach is needed when assessing these dynamic and environmentally critical habitats to include the effects of physical oceanographic controls across multiple spatiotemporal scales.

中文翻译：

---

盆地尺度海洋过程对热带海山生态系统内波状况的调节


由于浅海山作为生物避难所的作用，特别是在整个贫营养海洋中，浅海山越来越被认为是重要的保护栖息地。传统上，泰勒帽被认为是驱动海山生物量聚集的机制，但基于更高分辨率测量的新证据强调了内波（IW）对当地生态系统的重要性。这些波浪可以用来自深处的冷水冲洗底栖栖息地，并通过湍流混合在短时间内影响营养供应，这也可能影响鱼类的行为。然而，它们取决于区域分层，因此受到海洋条件的行星尺度变化的影响。我们在这里展示了印度洋中部一个称为 Sandes 的浅海山上的内波状况的详细观测结果，该海山在印度洋偶极子 (IOD) 的不同阶段调节了区域分层。 2019 年 IOD 事件引起的深温跃层排除了山顶上的内波活动，而 2020 年 IOD 极性反转时，温跃层与山顶并置，导致了 30 m 幅度的内潮信号（t ∼ 12.5 h）。 2022 年观测到的浅温跃层导致内潮在山顶传播，而内潮则不太明显。谐波分析显示，2020 年和 2022 年期间海山两侧均存在高频波（t ∼ 15 分钟），这可能是局部剪切不稳定的结果，而 2019 年则显示出不对称响应，可能是由于强背景电流以及顶峰深度以下温跃层的抑制。 山顶波浪对当地生态系统的潜在重要性可能归因于内部波浪传播期间在温跃层测量到的湍流升高，经常观察到 ε > 10 W kg-1。我们的结果强调了温跃层深度作为顶峰内波演化的门控条件的能力。这些结果表明，虽然与经常引用的泰勒盖动力学相比，水柱在短时空尺度上表现出变化，但它也受到更广泛的盆地尺度过程的调节。因此，在评估这些动态和环境关键栖息地时，需要采取更加综合的方法，以包括跨多个时空尺度的物理海洋学控制的影响。