Pan-Arctic Acoustic Archives: Quantifying zooplankton behaviours in a changing Arctic

北极正在迅速变化。最明显的变化之一是夏季海冰的范围和厚度的减少。由于气候变暖，预计未来几年冰的损失将会增加。到2030年，北极可能没有夏季海冰。至关重要的是，冰对阳光起到了遮阳的作用，当它退缩时，它使开阔的水域暴露在光照下，导致海洋植物（浮游植物）的生长迅速增加。这些植物从大气中消耗二氧化碳，因此是地球气候系统的重要组成部分。一旦形成，浮游植物就成为食草浮游动物的食物，食草浮游动物能够将这种碳源运送到更深的水域，在那里它被排泄并埋在沉积物中。这一过程被称为“生物泵”，它将碳从大气中转移并封存起来。了解冰、浮游植物、浮游动物和碳之间的关系是很重要的，这些关系可以在生物地球化学循环模型中进行模拟。这个链条的关键一环是食草浮游动物。它们有一种特殊的行为，称为“diel垂直迁移”（DVM），这是许多海洋生态系统的一个突出特征。这些动物在黎明和黄昏前后快速垂直移动数十到数百米，这是地球上生物量最大规模的周期性变化。经典观点认为，DVM是个体在获取食物和躲避捕食者之间进行的一种权衡。浮游动物在夜间向上移动，在近地表觅食，在那里进行初级生产。在这里，在黑暗的掩护下，视觉捕食者的风险降到最低。这种向上/向下的迁移将靠近地表的光合作用固定的碳重新分配到更深的水域，并且可能从大气中去除比其他情况下更多的二氧化碳，从而降低大气中二氧化碳积累的速度。由于通道和冰层覆盖，在北极全年研究浮游动物是很困难的。记录DVM行为的一种成功技术是使用一种称为声学多普勒电流分析器（ADCP）的仪器。在过去的十年里，许多adcp被部署在北极测量洋流，但声学信号也记录了浮游动物的迁徙。通常，分析这些数据只是为了了解仪器所在区域的洋流。我们正处于北极研究的关键时刻，我们必须对海洋过程采取更广泛的“泛北极”观点。我们建议与国际组织合作，整理、处理和存档ADCP数据，为研究DVM创造一个独特的资源。规律的、有节奏的行为意味着我们可以使用数字技术（昼夜节律分析）来量化迁徙行为的强度和规律性，并将其与现有的生物群落、光照水平和海冰覆盖量联系起来。我们将利用这些知识来改进浮游动物如何通过粪便将碳输送到深海的模型。了解浮游动物DVM很重要，原因有很多。量化DVM的行为将使我们能够提高预测海冰变化如何改变碳在多产的北极海洋中被捕获和储存方式的能力。这将使我们更深入地了解动物如何以及为什么进行这种有规律的迁徙，以及如何控制这些迁徙的时间。通过将声学数据与物种数据联系起来，我们将能够了解浮游动物在北极生态系统中的作用，如果要对依赖浮游生物的鱼类物种的影响进行预测，这一点尤为重要。

The Arctic is changing rapidly. One of the clearest changes is a reduction in the extent and thickness of summer sea ice. The loss of ice 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. Critically, the ice acts as a shade to sunlight and as it retreats it exposes open water to illumination causing a rapid increase in the growth of marine plants (phytoplankton). These plants use up carbon dioxide (CO2) from the atmosphere and are therefore an important component of Earth's climate system. Once formed, the phytoplankton become food for herbivorous zooplankton who are able to transport this source of carbon to deeper waters where it is excreted and buried in the sediments. This process, called the 'biological pump', transfers carbon from the atmosphere and locks it away. It is important that we understand the relationships between ice, phytoplankton, zooplankton and carbon and these relationships can be simulated in models of biogeochemical cycles. The critical link in this chain is the herbivorous zooplankton. They have a particular behaviour called 'diel vertical migration' (DVM) which is a prominent feature of many marine ecosystems. The 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. Zooplankton move upwards to feed at night into the nearsurface where primary production occurs. Here, under the cover of darkness, the risk from visual predators is minimised. This upward/downward migration redistributes carbon fixed by photosynthesis near the surface to deeper waters, and may remove larger quantities of CO2 from the atmosphere than would otherwise be the case, reducing the rate of CO2 accumulation in the atmosphere. Studying zooplankton in the Arctic year round is difficult because of access and ice cover. One successful technique for recording DVM behaviour uses an instrument called an acoustic Doppler current profiler (ADCP). Many ADCPs have been deployed in the Arctic over the last decade to measure currents but the acoustic signals also record zooplankton migrations. Usually these data are only analysed to understand the ocean currents within the localised region where the instrument was deployed. We are at a critical time in Arctic research where we must take a wider, 'pan-Arctic' view of marine processes. We propose to work with international groups to collate, process and archive the ADCP data, creating a unique resource for studying DVM. The regular, rhythmic behaviour means that we can use numerical techniques (circadian rhythm analysis) to quantify how strong and regular the migration behaviour is and relate this to the biological communities that are present, the level of illumination and the amount of sea ice cover. We will use this knowledge to improve models of how zooplankton transport carbon, through their faecal material, to depth. Understanding zooplankton DVM is important for many reasons. Quantifying DVM behaviour will allow us to improve our ability to predict how changes in sea ice might alter changes in the way carbon is captured and stored in the productive Arctic seas. It will give us a greater insight into how and why animals undertake such regular migrations and how the timing of these migrations is controlled. By relating the acoustic data with species data we will be able to understand the role of zooplankton in Arctic ecosystems and this is of particular importance if predictions on the effect of plankton-dependent fish species are to be made.