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

大陆架海通常不到200米深，可以用大陆大陆块周围的浅海来描述。由于其通达性，陆架海具有重要的商业和经济价值，仅英国陆架海的石油和天然气开采就价值37Bpa。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%以上的碳固定，并支持90%的全球渔获量，为不断增长的沿海人口提供关键的食物来源。然而，陆架海也暴露在气候驱动和人为压力下，这可能对其生物生产力、氧气动力学和生态系统功能产生深远影响。造成这一威胁的许多过程与经历垂直分层的区域有关。当陆架海的底层从近表层的大气通风中分离出来时，这个过程就会发生。在温带陆架海，层结主要是由于太阳加热胜过潮汐和风驱动的混合而产生温暖的表层，导致欧洲西北部陆架海大片地区的季节性层结。表层的物理脱离和底层生物耗氧量的增加，再加上上层海洋中层化所支持的生产力的提高，可能会导致底层氧气浓度急剧下降。当氧气水平变得如此低时，它们被归类为缺氧，这可能会给海底和远洋海洋生物带来问题，并对生态系统功能产生不利影响。有证据表明，AlterEco小组成员发现北海地区季节性缺氧症日益严重，而且全球陆架海和沿海缺氧症的严重程度已得到公认，迫切需要加强对氧气的空间和时间测量，并更好地了解导致陆架海底水缺氧的过程。生态系统功能的自然复杂性、气候变化的影响、陆架海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压力严重阻碍了这一需求。目前的方法在解决这一复杂性方面受到严重限制，因为观测覆盖的分辨率很低，这需要一种新的战略来观察和监测海洋生态系统和环境状况。AlterEco试图在特定呼吁的框架内通过开发新的监测框架来解决这一挑战，以更好地了解关键的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方面的投资和规划能力，对北海一个已知在整个季节性周期中经历不同物理、化学和生物条件的区域进行调查，包括被发现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公里的距离内进行重复横断面，足以捕捉重要的陆架海洋特征；例如锋面和涡流。AlterEco战略将使用小型车队来捕捉这些中尺度特征(通常为约100公里)，但也将解决亚中尺度变化(约100米)。我们将从最近开创性地部署水下滑翔机的成功经验和教训中受益，并使用一套传感器，使关键生态系统指标的高分辨率符合测量成为可能。结合AlterEco团队的专业知识，我们不仅将为具有全球可转换性的海洋观测提供新的框架，而且还将提供诊断能力，以提高对大陆架海洋生态系统健康和功能的了解。

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.