An Alternative Framework for Assessing Marine Ecosystem Functioning in Shelf Seas (AlterEco)

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.

In the UK alone, marine data collection costs approximately £80 million per year, but there is increasing pressure across sectors to reduce these costs. Coupled with public demand for open access, verifiability and the need for sharing data across different stakeholders and users, has led to the creation of the UK Integrated Marine Observing Network (UK-IMON). AlterEco will help achieve the aim of UK-IMON to provide the evidence base for future assessments of environmental status.

The UK government singled out "Robotics and autonomous systems" as one of "eight great technologies" with large economic growth potential (www.gov.uk/government/publications/eight-great-technologies-robotics-and-autonomous-systems). In the marine community alone, RCUK, Higher Education Institutions and industry have recently invested over £100 million in Smart and Autonomous Observing Systems. AlterEco will capitalise on this investment by using novel platforms and sensors to provide high-quality observations of shelf-sea dynamics, nutrient and carbon cycling. In turn, this will demonstrate how these new capabilities can be used together with existing techniques to help fulfill the UK's statutory requirements for monitoring water quality and Good Environmental Status, as mandated by the Marine Strategy Framework Directive (MSFD), the Convention on Biological Diversity and the OSPAR Convention. AlterEco will thus be of interest to stakeholders such as agencies with marine monitoring obligations (Defra, Cefas, Marine Scotland and AFBI) as well as the community of glider and sensor manufacturers and users as a whole. It will allow them to optimise target locations of their monitoring programme, make it more efficient and feed into future policy requirements.

Under the umbrella of the UK Marine Science Coordination Committee (MSCC), the UK Marine Assessment and Reporting Group oversees and coordinates the activities of the four UK Marine Monitoring and Assessment Strategy (UKMMAS) evidence groups (Clean and Safe Seas Evidence Group, Healthy and Biologically Diverse Seas Evidence Group, Productive Seas Evidence Group, Ocean Processes Evidence Group). AlterEco will provide part of the evidence required by these groups, in particular the latter three.

The data gathered by AlterEco will be archived at the British Oceanographic Data Centre (BODC), to make them available for historic analyses, model validation and testing. BODC, as well as NERC, Cefas, Marine Scotland and SAMS are partners of the Marine Environmental Data and Information Network (MEDIN), which provides a contractual framework and single-point of access portal and software tools to retrieve data from the network of specialist data archive centres contributing to it. Project results will also feed into international data infrastructures provided by the International Council for the Exploration of the Sea (ICES) and the European Marine Observation and Data Network (EMODNet).

The UK Met Office (UKMO) will be providing output to AlterEco from their coupled physical-biogeochemical NEMO-ERSEM model. In turn, real-time data from our project will be used for operational trialing of the assimilation of glider data into UKMO models, starting with temperature and salinity in September 2017 (from historical collated datasets), but then rapidly moving on to include biogeochemical variables (September 2018: chlorophyll a fluorescence; September 2019: oxygen concentrations), entraining real-time AlterEco data from our planned North Sea mission.

Other members of the ERSEM modelling community in the UK (NOC, PML, Cefas, UEA) and beyond will also greatly benefit from long-endurance, high-frequency physical and biogeochemical measurements delivered by AlterEco. This includes the consortium addressing Challenge 2 of the Autonomous Observations programme and will provide improved estimates and forecasts of oxygen deficiency in UK shelf seas.