Water column characteristics obtained by yoyo-CTD and mooring sensors and benthic organism abundance of a biologically rich seamount of the Mid-Atlantic Ridge

The turbulence regime near the crest of a biologically rich seamount of the Mid-Atlantic Ridge southwest of the Azores was registered in high spatial and temporal resolution. Internal tides and their higher harmonics dominate the internal wave motions, producing considerable shear-induced turbulent mixing in layers of 10±50 m thickness. This interior mixing of about 100 times open-ocean interior values is observed both at a high-resolution temperature sensor mooring-site at the crest, 770 m water depth being nearly 400 m below the top of the seamount, and a CTD-yoyo site at the slope off the crest 400 m horizontally away, 880 m water depth. Only at the mooring site, additionally two times higher turbulence is observed near the bottom, associated with highly non-linear wave breaking. The highest abundance of epifauna, notably sponges, are observed just below the crest and 100 m down the eastern slope (700±800 m) in a cross-ridge video-camera transect. This sponge belt is located in a water layer of depressed oxygen levels (saturation 63±2%) with a local minimum centered around 700 m. Turbulent mixing supplies oxygen to this region from above and below and is expected to mix nutrients away from this biodegraded layer towards the depth of highest abundance of macrofauna.

本数据集以高时空分辨率记录了亚速尔群岛西南侧大西洋中脊（Mid-Atlantic Ridge）一处生物富集海山（seamount）顶部附近的湍流状态（turbulence regime）。
内潮（Internal tides）及其高次谐波主导了区域内的内波运动，在厚度为10±50米的水层中产生显著的剪切诱导湍流混合（shear-induced turbulent mixing）。
观测到的该区域内部混合强度约为开阔大洋内部混合强度的100倍，相关观测分别在两处站位开展：一处为海山顶部的高分辨率温度传感器锚定站位，水深770米，距海山山顶近400米；另一处为海山侧翼距顶部水平距离400米的温盐深仪（CTD）往复观测站位，水深880米。
仅在该锚定站位的近底区域，观测到湍流强度较基准提升一倍，该现象与高度非线性的波浪破碎过程相关。
跨脊视频断面观测显示，底上动物（epifauna）尤以海绵（sponges）为代表的丰度最高值出现在海山顶部下方以及东坡向下100米处（水深700±800米）。
该海绵带所处水层的氧含量低于周边，氧饱和度为63±2%，局部最低值中心位于约700米深度处。
湍流混合从上下两个方向为该区域补给氧气，并可将营养物质从该生物降解层输运至大型底栖生物（macrofauna）丰度最高的深度区间。