Clearing the Water on Ecosystem-Level Effects of Seawater Turbidity on the North West European Shelf.

Seawater turbidity influences primary production, nutrient exchanges and the carbon cycle in our oceans. As turbidity is likely to increase throughout the twenty-first century, due to factors including the increased occurrence of storm events and anthropogenic pressures, the potential impacts on ecosystems must be investigated. Greater understanding of the relationship between light availability and ecosystem health will aid in forecasting the future biogeochemical state of shelf seas under a changing climate.

Seven sites across the North West European Shelf (NWES) are investigated to generate a picture of the impacts of turbidity in different environmental settings. For example, study sites with differing salinity concentrations, stratification or proximity to land represent the varied conditions around the British Isles. Hindcast data is crucial for depicting seasonal and interannual patterns in seawater turbidity on the shelf since 1990. We show that changes to chlorophyll increase turbidity on the NWES. Furthermore, the total optical absorption coefficient of water indicates turbidity across the shelf. In-situ measurement and earth observation data will also be used to calibrate model parameters and verify model outputs.

The hydrodynamic-ecosystem model ERSEM is used to represent the 1D water column. As light availability within the water column is determined by organic and inorganic particles, the specific shortwave backscattering properties (m²/mg C) of particulate organic matter (POM) are altered to represent greater turbidity. The effects on biogeochemistry, carbon, phytoplankton and zooplankton are studied to assess the response of the ecosystem to higher turbidity in European shelf seas. Results suggest that increasing the backscattering of POM has different impacts depending on environmental conditions. Increasing backscattering in the North Sea reduced microphytoplankton. Conversely, increased backscattering in the North Atlantic increased microphytoplankton.

Here we present the results of the 1D ERSEM turbidity analysis and supporting hindcast observational conclusions. Findings from the 1D ERSEM analysis and hindcast data will be utilized to inform the 3D ERSEM modelling of suspended particulate matter across the NWES. Future work will incorporate these findings into generating two environmental scenarios (such as increased temperature along with increased storminess and higher riverine discharge) to forecast the potential future of seawater turbidity on the NWES.