An Alternative Framework to Assess Marine Ecosystem Functioning in Shelf Seas (AlterEco)

大陆架海通常深度不到200米，可以用围绕大陆块的浅海来描述。由于其可达性，大陆架海域具有重要的商业和经济价值，仅英国大陆架海域的石油和天然气开采价值就高达每年370亿英镑。尽管陆架海只占表层海洋的7%，但它在全球碳循环和海洋生态系统中也发挥着重要作用。陆架海的生产力是公海的3-4倍，估计支持40%以上的碳固存，支持全球90%的鱼类捕捞，为不断增长的沿海人口提供了重要的食物来源。然而，陆架海也面临气候驱动和人为压力，这可能对其生物生产力、氧动力学和生态系统功能产生深远影响。造成这种威胁的许多进程都与经历垂直分层的区域有关。当陆架海的底层与大气通风的近表层分离时，这一过程就会发生。在温带大陆架海域，分层主要发生在太阳加热超过潮汐和风驱动的混合，产生温暖的表层，导致欧洲西北部大陆架海域的大片地区出现季节性分层。与表层的物理分离和底层生物耗氧量的增加，再加上上层海洋分层所支持的生产力的提高，可能导致底层氧气浓度急剧降低。当氧气水平如此之低时，它们就被归类为缺氧，这对底栖生物和远洋海洋生物来说可能是一个问题，对生态系统功能有不利影响。AlterEco团队成员提出的证据表明，北海地区季节性缺氧的增加，以及大陆架海和沿海缺氧的全球范围的增加，迫切需要增加氧气的时空测量，并更好地了解导致大陆架海底缺氧的过程。生态系统功能的自然复杂性、气候变化的影响、大陆架海洋不同区域之间的连通性以及来自海洋和大气的大规模外部强迫，严重阻碍了这一需求。由于观测范围的分辨率较低，目前的方法在解决这种复杂性方面受到严重限制，这需要一种新的观测和监测海洋生态系统和环境状况的战略。AlterEco试图通过开发一种新的监测框架来解决这一挑战，从而更好地了解关键的大陆架海洋生态系统驱动因素。我们将利用英国最近在海上自动驾驶车辆和规划能力方面的投资，调查北海在整个季节周期中经历各种物理、化学和生物条件的区域，包括确定在夏季经历低底层氧气水平的区域。海洋滑翔机将用于在约150公里的距离上进行重复横断面，足以捕捉重要的大陆架海洋特征；比如锋面和漩涡。AlterEco战略将采用小型车队来捕捉这些中尺度特征（通常为100公里），但也可以解决亚中尺度变化（约100米）。我们将从最近开创性的水下滑翔机部署中获得成功和经验教训，并使用一套能够对关键生态系统指标进行高分辨率同步测量的传感器。结合AlterEco团队的专业知识，我们不仅将提供具有全球可转移性的海洋观测新框架，而且还将提供诊断能力，以提高对陆架海洋生态系统健康和功能的理解。

Continental shelf seas are typically less than 200m deep and can be described by the shallow ocean surrounding continental land masses. Due to their accessibility, shelf seas are commercially and economically important, with oil and gas extraction alone in UK shelf seas valued at £37B pa. Despite occupying only 7% of the surface ocean, shelf seas also play a major role in the global carbon cycle and marine ecosystem. Shelf seas are 3-4 times more productive than open-ocean, are estimated to support more than 40% of carbon sequestration and support 90% of global fish catches providing a critical food source for growing coastal populations. However, shelf seas are also exposed to climate driven and anthropogenic stress that could have a profound impact on their biological productivity, oxygen dynamics and ecosystem function. Many processes contributing to this threat are related to regions that undergo vertical stratification. This process occurs when the bottom layer of shelf seas becomes detached from the atmospherically ventilated near surface layer. In temperate shelf seas stratification predominantly occurs as solar heating outcompetes the tide and wind-driven mixing to produce a warm surface layer, resulting in seasonal stratification over large areas of the NW European shelf seas. A combination of physical detachment from the surface and increased biological oxygen consumption in the bottom layer, accentuated by the enhanced productivity that stratification also supports in the upper ocean, can result in a drastically reduced bottom layer oxygen concentration. When oxygen levels get so low, they are classified as being oxygen deficient and this can be problematic for benthic and pelagic marine organisms and have a detrimental effect on ecosystem function. Evidence of increasing seasonal oxygen deficiency in the regions of North Sea by members of the AlterEco team and a recognised global increase in the extent of shelf sea and coastal oxygen deficiency calls for an urgent need to increase the spatial and temporal measurement of oxygen and a better understanding of the processes that lead to oxygen deficiency in shelf sea bottom waters. This need is severely impeded by the natural complexity of ecosystem functioning, the impact of a changing climate, connectivity between different regions of our shelf seas and large-scale external forcing from ocean and atmosphere. Current methods are severely restricted in resolving this complexity, due to the poor resolution in observational coverage, which calls for a new strategy for observing and monitoring marine ecosystem and environmental status.AlterEco seeks to address this challenge within the framework of the given call by the development of a novel monitoring framework to deliver improved understanding of key shelf sea ecosystem drivers. We will capitalise on recent UK investments in marine autonomous vehicles and planning capability to investigate an area of the North Sea known to undergo variable physical, chemical and biological conditions throughout an entire seasonal cycle, including areas identified to experience low bottom layer oxygen levels during summer months. Ocean gliders will be used to undertake repeat transects over a distance of ~150km, sufficient to capture important shelf sea features; such as fronts and eddies. The AlterEco strategy will employ small fleets of vehicles to capture these meso-scale features (typically ~100km in scale) but will also resolve sub-mesoscale variability (~100m). We will benefit from successes and lessons learnt from recent, pioneering deployments of underwater gliders and use a suite of sensors that permit high-resolution coincident measurements of key ecosystem indicators. Combining the expertise within the AlterEco team we will not only provide a new framework for marine observations that has global transferability, but also the diagnostic capability to improve understanding of shelf sea ecosystem health and function.