Impact of Arctic sea-ice retreat on zooplankton foraging behaviour and vertical carbon flux

浮游动物昼夜垂直迁移是许多海洋生态系统的显著特征。动物在黎明和黄昏时垂直移动数十到数百米，这是地球上生物量最大的周期性迁移。经典的观点是DVM是个体在食物获取和捕食者回避之间的权衡。食草性浮游动物在夜间在黑暗的掩护下向上移动，在近地表觅食，那里发生初级生产，但视觉捕食者的风险最大。这种向上/向下的迁移将地表附近通过光合作用固定的C重新分配到更深的沃茨，并可能降低大气CO2积累的速率。在公海，DVM的周期性随纬度和季节的变化而变化，因为白天的长度不同。其发生和幅度也可能随着光照强度的变化而变化，导致在高纬度地区连续日光下出现不寻常的模式。海冰覆盖对底层沃茨的物理（如阴影）和生物（如减少光合作用和排除表面潜水捕食者）产生影响，因此可能影响浮游动物的丰度/行为。然而，由于与冰下取样有关的重大后勤困难，对那里浮游生物的行为知之甚少。北极的海冰已经在减少，由于气候变暖，预计未来几年的损失率将增加。到2030年，北极可能没有夏季海冰。冰的损失很可能会改变浮游生物的行为，并对该地区的碳循环产生重大影响。此外，大多数冰最初将在北极边缘周围的浅水沿海地区消失，那里的渔业产量最大：如果要预测依赖南极洲的鱼类物种的影响，了解浮游动物的后果也至关重要。我们建议利用斯瓦尔巴特群岛无冰和季节性冰层覆盖的峡湾中已有的系泊设施（科学仪器悬挂在固定在海床上的浮标上）（由"海洋2025"和挪威研究理事会支持）。80度在大西洋），以探索浮游动物的行为全年在这些对比鲜明的环境。系泊设备配备了声学多普勒海流剖面仪（ADCP），可以跟踪浮游生物的迁移，沉积物捕集器，收集浮游生物及其粪便，以及温度和盐度探头，以监测水柱的物理特性。站点之间的任何明显差异都将有助于了解冰损失如何影响这一敏感区域的海洋生态，并将有助于预测冰退缩后目前被冰覆盖的位置的未来变化。这项工作符合海洋2025战略目标13“北极大陆架时间序列”。数据将在一个模型框架中进行探索，该模型框架将告诉我们浮游动物产生的粪便颗粒有多少通过饱足下沉的过程被输出到深处，即在表面进食并沉入海洋内部消化，这可能会在白天和晚上发生多次。如果没有这种行为，大多数粪便颗粒将留在表层并被回收。然而，在浮游动物进行饱足下沉的地方，被隔离在海洋内部的C粒子的量可能增加10 - 25%。冰的存在和持续的光照可能会影响饱足下沉，我们将衡量这些因素对碳封存的影响。我们在浮游生物迁移和海冰系统方面有相当丰富的工作经验。我们在这里的合作努力有可能为已经资助的系泊部署提供更多的附加值，并提高预测北极变化的生态系统后果的能力。该项目将加强英国机构与在斯瓦尔巴群岛和更广泛的北极地区工作的其他欧洲/斯堪的纳维亚组织之间的合作。

Diel vertical migration (DVM) by zooplankton is a prominent feature of many marine ecosystems. Animals move quickly tens to hundreds of meters vertically around dawn and dusk in migrations that comprise the most massive periodic shifts in biomass on Earth. The classical view is that DVM occurs as a trade off by individuals between food acquisition and predator avoidance. Herbivorous zooplankton move upwards to feed at night under the cover of darkness in the near-surface where primary production occurs but where the risk from visual predators is greatest. This upward/downward migration redistributes C fixed by photosynthesis near the surface to deeper waters, and may reduce the rate of atmospheric CO2 accumulation. In the open sea DVM periodicity varies with latitude and season as day length varies. The occurrence and amplitude may also vary as a function of light intensity, resulting in unusual patterns at high latitudes during continuous daylight. Sea ice cover impacts underlying waters physically (eg shading) and biologically (eg reducing photosynthesis and excluding surface diving predator) and so may impact zooplankton abundance/behaviour. However, due to major logistic difficulties associated with sampling under ice, little is known about the behaviour of plankton there. Sea ice in the Arctic is already reducing, and the rate of loss is predicted to increase in the coming years as a consequence of climatic warming. There may be no summer sea ice in the Arctic by 2030. The loss of ice may well change the behaviour of plankton and impact significantly on C cycling in the region. Furthermore, most ice will be lost initially around the Arctic rim, over the shallow coastal seas where fisheries production is greatest: understanding consequences to zooplankton will also be vital if predictions on the effect of plankton-dependent fish species are to be made. We propose taking advantage of moorings (scientific instruments suspended in mid water on floats anchored to the seabed) already in place (supported by 'Oceans 2025' and the Norwegian Research Council) in ice-free and seasonally ice-covered fjords at Svalbard (c. 80 deg N in the Atlantic) to explore zooplankton behaviour year-round in these contrasting environments. The moorings are equipped with acoustic Doppler current profilers (ADCPs) that can track plankton migrations, sediment traps that collect plankton and their fecal matter, and temperature and salinity probes to monitor watercolumn physical properties. Any apparent differences between sites will give useful insights into how ice loss may affect the marine ecology of this sensitive region, and will help to predict future changes in presently ice-covered locations following ice retreat. This work fits with Oceans 2025 Strategic Objective 13 'Arctic Shelf Time Series'. Data will be explored in a model framework that will tell us how much fecal pellet production by zooplankton is exported to depth through the process of satiation sinking i.e. feeding at the surface and sinking into the ocean interior to digest, which can occur many times over the day and night. When this behaviour is absent most fecal pellets will remain in the surface layers and be recycled. Where zooplankton perform satiation sinking however, the amount of C particles sequestered in the ocean interior may be increased by 10-25%. The presence of ice and also of continuous light is likely to affect satiation sinking, and we will gauge what effect these factors have on carbon sequestration. We have considerable experience working on plankton migrations and on sea-ice systems. Our collaborative efforts here have the potential to provide much added value to already-funded mooring deployments, and to lead to an improved capacity to predict ecosystem consequences of change in the Arctic. The project will strengthen collaborations between UK institutions and other European/Scandinavian organisations working in Svalbard and in the wider Arctic.