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

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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.