Understanding the dynamics of the phytoplankton spring bloom and predicting its fate and impact on marine ecosystems in the Arctic Ocean of tomorrow

在世界海洋的大部分地区，浮游植物春季水华（PSB）提供了很大一部分的年度初级生产力（PP），最重要的是，几乎所有的新PP输出通过食物链和底部沉积物。在北冰洋（AO），光合细菌通常在冰缘附近发展。这种高度瞬变的现象在季节性冰区（SIZ）的任何给定位置持续约3周，并占AO年度PP的大部分。SIZ目前正在扩大规模，到2030年代可能覆盖整个AO。因此，人们可能会想，冰缘水华是否会通过显著的向北扩张，覆盖比过去大得多的区域。如果是这样的话，这些额外的浮游植物生物量将如何在沿着消退的冰盖上积聚。它是否会维持较高的中上层食物网次级生产和营养转移，从而使巨型动物受益？或者它会迅速下沉并产生新的海底热点，可能有助于增加沉积物中的碳固存？本项目的总体目标是了解控制北极光合细菌向北扩展的过程，并通过调查其相关的碳通量来确定其在生态系统中的命运。该项目的短期目标是了解北极光合细菌的动态，更具体地说，了解它是如何受到上层海洋的物理和化学特性以及水华期间浮游植物物种演替的控制。长期目标是在不断变化的AO中确定PSB的命运。我们推测，PP在高纬度地区将增加，在未来几十年内，因为向北扩展的SIZ和加强的浮游植物春季水华。浮游植物物候的变化可能对整个生态系统和食物链产生深远的影响。 将在巴芬湾监测PSB事件，从5月在融冰下开始，到7月在SIZ结束。将使用剖面浮标、滑翔器和配备物理和生物光学传感器的自主水下航行器，以不同比例描述相关的物理、化学和生物特性。将进行过程研究，以记录浮游植物生长、营养同化和碳通过食物网向沉积物转移的情况。关键的浮游植物物种将在实验室条件下分离和生长，以模拟其物种演替和对环境因素的反应。我们将使用海洋颜色遥感彻底研究北极PSB，浮游植物生物量的完整物候，以及由强迫事件（如陆架断裂上升）引发的短暂浮游植物水华。冰缘附近海水的光学特性及其在春季水华期间的变化将用于优化我们的海洋颜色算法，我们将建立一个泛北极PP的时间序列，在此期间，遥感海洋颜色数据可用。最后，一个耦合的物理-生物模型将被优化，以模拟北极光合细菌和预测浮游植物群落和食物网动态在各种时间尺度上的变化。 该项目是一项前所未有的努力，通过使用最先进的实地和实验室观测技术、海洋颜色遥感和复杂的建模工具，对AO中的PSB进行机械理解。从该项目中获得的知识将扩大我们的观测能力和对北极生态系统发生的快速变化的了解。

In most parts of the World Ocean, the phytoplankton spring bloom (PSB) provides a large fraction of the annual primary production (PP) and, most importantly, nearly all of the new PP exportable through the food chain and toward the bottom sediments. In the Arctic Ocean (AO) the PSB often develops around the ice-edge. This highly transient phenomenon lasts about 3 weeks at any given location in the seasonal ice zone (SIZ) and accounts for most of the annual PP in the AO. The SIZ is currently increasing in size and may cover the entire AO as of the 2030s. Therefore, one may wonder whether ice-edge blooms will cover a much larger area than they used to through a significant northward expansion. If so, what will be the fate of this additional phytoplankton biomass build-up along the retreating ice cover. Will it sustain higher secondary production and trophic transfer in the pelagic food web, thus benefiting megafauna? Or will it sink rapidly and create new benthic hotspots, possibly contributing increased carbon sequestration in the sediment? The overarching goal of the present project is to understand the processes that control the Arctic PSB as it expands northward and to determine its fate in the ecosystem by investigating its related carbon fluxes. The short-term objective of this project is to understand the dynamics of the Arctic PSB and, more specifically, how it is controlled by physical and chemical properties of the upper ocean and by phytoplankton species succession during the bloom. The long-term objective is to determine the fate of the PSB in a changing AO. We hypothesize that PP at high latitudes will increase in the coming decades because of a northward expansion of the SIZ and an intensification of the phytoplankton spring bloom. Changes in the phytoplankton phenology may have profound consequence on the entire ecosystem and food chain. A PSB event will be monitored in Baffin Bay from its onset under melting ice in May to its conclusion in the SIZ in July. Relevant physical, chemical and biological properties will be described at various scales using profiling floats, gliders and an autonomous underwater vehicle, equipped with physical and bio-optical sensors. Process studies will be conducted to document phytoplankton growth, nutrient assimilation and carbon transfer through the food web and towards the sediment. Key phytoplankton species will be isolated and grown under laboratory conditions to model their species succession and response to environmental factors. We will use ocean color remote sensing to thoroughly study the Arctic PSB, the full phenology of phytoplankton biomass, as well as transient phytoplankton blooms triggered by forcing events such as shelf-break upwellings. The optical properties of seawater in the vicinity of the ice edge and their variations during the spring bloom will be used to optimize our ocean colour algorithms and we will establish a time series of pan-Arctic PP over the period for which remotely sensed ocean colour data are available. Finally, a coupled physical-biological model will be optimized to simulate the Arctic PSB and predict changes in phytoplankton communities and food web dynamics over a variety of temporal scales. The project is an unprecedented effort for gaining a mechanistic understanding of the PSB in the AO through the use of state-of-the-art field and laboratory observation technologies, remote sensing of ocean colour and sophisticated modelling tools. The Knowledge gained from this project will expand our observational capacity and knowledge of the rapid changes taking place in Arctic ecosystems.