Changes in vertical and spatial distributions of zooplankton and small pelagic fish impact the biological carbon pump and the distribution of larger piscivorous fish and marine mammal species. However, their distribution and abundance remain poorly documented at high latitudes because of the difficulties inherent to sampling relatively fast-moving organisms in ice-covered waters. This study documents the under-ice distribution of epipelagic and mesopelagic organisms at the Arctic-Atlantic gateway in spring, during the midnight sun period, using ice-tethered and ship-based echosounders. An epipelagic surface scattering layer composed of copepods consistently occupied the top 60 m and was associated with cold polar surface water (mean temperature of −1.5 °C). A mesopelagic deep scattering layer (DSL), partly composed of fish, persisted between 280 m and 600 m and was associated with modified Atlantic water. Backscattering strength within the DSL was higher than previously reported in the Arctic and north Atlantic, and increased by two orders of magnitude over the continental slope where one of the Atlantic water pathways enters the Arctic Ocean. Mesopelagic organisms did not perform diel vertical migrations. The consistent segregation between copepods at the surface and their predators at mesopelagic depths suggests limited predator–prey interactions during the midnight sun period, even under the ice cover. Predation on copepods by mesopelagic organisms, including fish, could thus be limited to very pulsed events during the seasonal vertical migration of copepods to and from overwintering depths. This suggests that the arctic mesopelagic food web may be decoupled from secondary production in the epipelagic layer throughout most of the year.

浮游动物和小型浮游鱼类的垂直和空间分布的变化会影响生物碳泵以及大型食鱼和海洋哺乳动物的分布。但是，由于在冰雪覆盖的水中采样相对快速移动的生物体固有的困难，因此在高纬度地区，它们的分布和丰度仍然缺乏记录。这项研究记录了春季，午夜太阳期间，北极和大西洋中冰层上层和中生层生物在冰下的分布，这些冰层和冰层回波探测器是通过船用冰栓式和基于船的回声测深仪进行的。由co足类动物组成的上表层表面散射层始终占据顶部60 m，并与冷极性地表水（平均温度为-1.5°C）相关。中生深散射层（DSL），部分由鱼组成，持续时间在280 m至600 m之间，并伴有改良的大西洋水。DSL内的反向散射强度高于先前在北极和北大西洋报道的强度，并且在大西洋水路之一进入北冰洋的大陆坡上增加了两个数量级。中古生力生物不执行diel垂直迁移。表面上的co足类与其中捕食者深度的食肉动物之间的持续隔离表明，即使在冰盖下，在午夜的太阳期间，食肉动物与猎物之间的相互作用也很有限。因此，中ela足动物（包括鱼类）对co足类的捕食可能仅限于co足类在越冬深度上下季节性季节性迁徙期间的非常脉冲化的事件。