Collaborative Research: Atmospheric Forcing and the North Atlantic Spring Bloom

这项提议的目标是确定容易观察到的物理过程是否控制了北大西洋浮游植物水华的启动。该假说认为，水华是由冬末早春的混合减少引发的，此时热量损失和风力减弱。对于一个具有广泛生物参数的简单浮游植物-营养系统，水华在春季表层冷却转变为加热时，在现实的上层海洋对流湍流模型中发展起来。这项工作假设，湍流的变化很容易从可观察到的特性中预测出来，并且足够强烈，足以在任何允许它们的生物模型中引发水华。与之前对生物相互作用的细节非常敏感的解释不同，这种大气强迫假说可以用远程和现场数据进行检验，这些数据可以比生物数据更好地约束物理参数。这个项目将扩展我们现有的水华启动标准，以考虑风强迫、蒸发和降水。将评估该标准适用的生物学模型和参数的范围。这一理论将使用数值模拟、新的滑翔机数据(有待收集)、已建立的英国时间序列站和可用的卫星数据进行验证。关于控制水华形成的过程的持续激烈的辩论在很大程度上是由于缺乏可检验的假说和合适的现场数据。经过生物海洋学界对这一主题60年的研究，理论和技术现在已经足够先进，我们可以解决物理过程和水华发生时间之间相互作用的基本悬而未决的问题。因此，这项建议以短期(渔业)和长期(气候变化)与社会相关的主题为目标。该提案通过培训一名研究生和一名博士后，在对我们理解气候系统日益重要的问题上进行跨学科研究，具有很强的教育成分。与英国同事的国际合作收集相关数据是另一个重要方面。

The goal of this proposal is to determine whether easily observed physical processes control phytoplankton bloom initiation in the North Atlantic. The hypothesis is that blooms are triggered by a reduction in mixing in late winter/early spring when heat loss and winds weaken. For a simple phytoplankton-nutrient system with a wide range of biological parameters, blooms develop in realistic models of convective turbulence in the upper ocean when the surface cooling changes into heating in spring. This work hypothesizes that the change in turbulence is readily predicted from observable properties and is strong enough to spark a bloom in any biological model that admits them. Unlike previous explanations which are very sensitive to details of the biological interactions which are both poorly understood and difficult to quantify, this atmospheric forcing hypothesis is testable with remote and in-situ data which can constrain physical parameters much better than biological ones. This project will extend our existing criterion for bloom initiation to account for wind forcing, evaporation and precipitation. The range of biological models and parameters for which the criterion works well will be assessed. The theory will be tested using numerical simulations, new glider data (to be collected), an established UK time-series station, and available satellite data. The proposed project is a timely, unique and cost-effective opportunity to address one of the longest-running and most intensively studied problems in oceanography.The spring bloom, an annual population explosion that dominates the seasonal cycle of phytoplankton abundance in much of the global ocean, exemplifies the interplay between ocean biology and physics. The continuing lively debate on the processes controlling bloom initiation is driven largely by the paucity of testable hypothesis and suitable in-situ data. After 60 years of research into this topic by the biological oceanography community, theory and technology has now advanced sufficiently to the point where we can resolve fundamental outstanding questions on the interactions between physical processes and bloom timing. By coupling modern turbulence and biological models, driving them by observed atmospheric forcings, and comparing results with observations, we will determine the degree to which aspects of the bloom can be predicted simply by knowing the forcing and gain a deeper understanding of the phenomenon.Phytoplankton blooms in the North Atlantic are important for driving ocean carbon uptake and supporting ecosystems, including the fisheries of the North Americas and Europe. Hence this proposal targets topics of relevance for society both in the short term (fisheries) and long term (climate change). The proposal has a strong educational component through the training of a graduate student and a postdoc in interdisciplinary research on topics of growing importance for our understanding of the climate system. The international collaboration with UK colleagues to collect relevant data is another important aspect.