AlterEco will be managed through four workpackages, three of which will address key scientific challenges and a final synthesis workpackage that will draw together results to address the overarching aim of this proposal.
Team: Mark Inall, Matthew Palmer, Karen Heywood, Rob Hall, Andrew Dale and Matt Toberman.
Hypothesis to address: Inter-annual variability in the seasonal cycle of shelf seas physical structure is predominantly driven by large scale boundary forcing.
- Research shows that the physical structure of European shelf seas form and change seasonally, the timing, duration and magnitude of the seasonal cycle is controlled primarily by ocean boundary and atmospheric exchange. The second order processes such as density currents and baroclinic circulations are dependent of the previous years’ physical conditioning of the shelf seas. This is demonstrated by the variable level of coupling over inter-annual variability over European Shelf seas and the coastal seas with North Atlantic.
To understand inter-annual variability across the shelf sea interior requires detailed knowledge of the connectivity between hydro-climatic forcing, seasonal and shorter time-scale cycles and meso to sub-mesoscale physical features.
- Demonstrate the effectiveness of the chosen observational strategy to resolve both tidal-to-seasonal and micro-to-mesoscale variability in temperature, salinity and meteorological conditions.
- Assess historical and sustained observational data to relate open-ocean physical forcing to central North Sea variability.
- Provide interpretation of new observations of meso and sub-mesoscale physical features and variability collected during AlterEco relative to large-scale and hydro-climatic conditioning.
- Provide suitable indices for North Sea physical conditioning and conditions for comparison with chemical and biological analytical products arising from WP2 and 3.
- Collated, multi-decadal time-series of North Atlantic physical conditioning of North Sea physical structure.
- Quantifiable correlative statistics describing open-ocean and central North Sea physical connectivity.
- Time series of vertical and horizontal fluxes and transports of physical properties from collected AlterEco and partner deployments and surveys.
Team: Jan Kaiser, Tim Smyth, Jeroen van der Kooij, Angus Atkinson, Ben Loveday and Bastien Queste.
Hypothesis to address: Spatial gradients in the duration and the intensity of stratification control the distribution of phytoplankton and zooplankton biomass and annually integrated productivity.
- Phytoplankton spring bloom, triggered and controlled by the physical conditions of stratification on the water column, is a key event in the shelf sea as it is the major source of food to higher trophic levels. Following the spring bloom shelf seas undergo prolonged periods of limited primary production that is dependent on subtle physical and biogeochemical interactions within the stratified water column. Autumn and winter conditions eventually break down the stratification, often producing a second phytoplankton bloom with reintroduction of nutrients from deeper water to the surface. While these seasonal cycles are loosely understood, ecosystem response to subtle variations in seasonal physical conditioning is not resolved: currently it is not possible to predict the timing, duration and intensity of a bloom or the effects of this variability on food web structure and ecosystem function.
For systematic understanding of ecosystem function and health, key physical and biogeochemical drivers must be directly connected to ecosystem response. This requires sustained, high-resolution observations over temporally and spatially varying conditions.
- Demonstrate the use of autonomous vehicles for quantitative assessment of the spatial variability in winter nitrate, oxygen and chlorophyll a concentrations.
- Assess the relationship between nutrients, phytoplankton and zooplankton along a gradient of distinct physical regimes over 4 key periods in the seasonal cycle.
- Estimate rates of net and gross biological production using oxygen and nitrate mass balances, vertical irradiance and chlorophyll a profiles.
- Assess the drivers of patchiness in plankton abundance and productivity rates.
- Depth, seasonally and spatially resolved distribution of nitrate, oxygen and chlorophyll a concentrations.
- Depth, seasonally and spatially resolved variability in net and gross phytoplankton production.
- Surface phytoplankton abundance and community size structure.
- Calibrated depth, seasonally and spatially resolved variability in zooplankton and fish abundance and distribution.
- Identify key zooplankton indicators that can be measured with state-of-the-art echosounders.
Team: Claire Mahaffey, Jonathan Sharples, Naomi Greenwood, Matthew Palmer.
Hypothesis to address: Spatial gradients in stratification, water depth and productivity control the development and intensity of oxygen deficiency in the North Sea.
- Oxygen deficiency in the bottom mixed layer is observed during summer in the seasonally stratifying regions of the North Sea. It is controlled by the seasonal duration of the stratification, volume and the productivity of the bottom mixed layer however, the relative contribution of multiple factors and how their contributions vary in time over different physical and meteorological conditions are poorly understood.
As the intensity and the extent of oxygen depletion increases, there is an urgent need to better understand the relative importance of physical versus biological drivers of the development of oxygen deficient regions.
- Resolve spatial and temporal variation in oxygen concentrations and saturation in the North Sea, alongside physical and biological drivers of oxygen deficiency.
- Assess the relationship between oxygen saturation and nitrate to quantify the magnitude of organic matter remineralisation in the bottom mixed layer.
- Quantify the role of turbulence in the exchange of oxygen between the oxygen replete surface waters and the oxygen deplete bottom mixed layer in the North Sea over seasonal and spatial scales.
- Estimate the relative contribution of thermal stratification, productivity and organic matter remineralisation, bottom mixed layer volume and turbulent mixing in driving spatial and temporal variation in bottom mixed layer oxygen deficiency in the North Sea.
- A continuous seasonal time-series of oxygen concentration covering temporally and spatially variable physical and biological conditions that are descriptive of European shelf seas.
- Time-series of turbulent diffusion of oxygen and nutrient gradients covering several spring-neap cycles during critical seasonal transition periods.
- Correlative diagnostics of linkages between oxygen concentration, turbulent mixing, stratification, water column depth, plankton biomass, productivity and remineralisation.
Team: Matthew Palmer, Naomi Greenwood, Jonathan Sharples, Tim Smyth, Jan Kaiser and Mark Inall.
Hypothesis to address: Long-term variability of dominant physical and biogeochemical drivers mean that static “baseline” conditions for shelf seas do not exist.
- The concept of “baseline” or reference conditions against which current sttus or function can be compared is fundamental to all assumptions of good environmental status (GES) and marine ecosystem assessment. Evidence suggests however that many of the descriptors and indicators of GES of marine ecosystems undergo significant inter-annual or multi-year variability, underwritten by long-term hydro-climatic trends and complex ecosystem feedbacks, resulting in an ever-shifting “baseline”.
Interpretation of current environmental status requires an improved definition of baselines that incorporates the consequences of inter-annual variability in both pre-conditioning and seasonal development of ecosystems.
- Bring together the physical, chemical and biological results and findings from WP1-3.
- Assess the effectiveness of the chosen methodology in deliver the AlterEco overarching aim “to developa novel monitoring framework to deliver improved spatio-temporal understanding of key shelf sea ecosystem drivers”.
- Deliver key datasets and knowledge to Challenge 2 of this call to contribute to efforts to “more efficiently predict and monitor the status of the shelf sea ecosystem”.
- Work with Challenge 2 to achieve the overarching aim of the call to “accelerate the use of autonomous measurements and combined observational-model outputs in meeting long-term science need and statutory policy requirements”.
- A quality controlled, high-resolution, seasonal time series including identified key parameters for assessment of ecosystem function and health.
- Assessment of the AlterEco experimental framework in providing long-term measurement and monitoring capacity in the UK shelf seas.