Pycnocline Mixing in Shelf Seas

The continental shelf seas provide a transition zone between estuaries and the ocean across which carbon, nutrients, sediments and contaminants are exchanged. The currents and mixing on the NW European continental shelf are dominated by the tide interacting with the sea bed, with density stratification occurring during summer months across ~80% of the region. Significant levels of biological primary production occur in these regions. However, the exchange of nutrients and carbon across these critical interfaces of stratified fluid is poorly understood and so is poorly represented in numerical models.
This project aims to compile the world's largest observational data base of shelf sea pycnocline turbulence and hydrographic measurements and to exploit state-of-the-art computer modelling and new observational technology to investigate, quantify, and parameterise the physical mechanisms and processes responsible for the fluxes across this critical interface. In particular we will develop improved understanding of pycnocline turbulence and mixing promoted by shear instability. We will test the hypothesis that these mechanisms, or interaction between mechanisms, drives pycnocline shear to levels which exceed a critical threshold beyond which there is a catastrophic loss of stability resulting in episodic mixing. Parameterisations for this mixing will be developed and tested.

This project has potentially a wide range of beneficiaries. As well as the benefits to the academic community in synthesising the world's largest shelf sea microstructure data base; developing an LES tool that would work like a 1D mixing model; and delivering a parameterisation to a key aspect of shelf sea modelling, namely the ability to simulate vertical mixing in stratified waters, there are some significant indirect benefits:

Science into Policy: Marine turbulence is an underlying control of many ecosystem processes (e.g. primary production and plankton community structure, so up the food chain through fish to piscivorous fish, sea birds and marine mammals). Modelling is a crucial tool in developing an ecosystem approach to marine management, since it can take a 'whole-systems' approach and has the potential for predictive capability. Hence the model development proposed here directly benefits several areas of marine policy, specifically the Marine Strategy Framework Directive and our understanding of the descriptors of Good Environmental Status1 therein, and their vulnerability to change (Descriptor 3: Population of commercial fish / shell fish; Descriptor 4: Elements of marine food webs; Descriptor 5: Eutrophication; Descriptor 7: Alteration of hydrographical conditions). The potential beneficiaries are UK and European policy makers: DEFRA, European Environment Agency, OSPAR. These issues are generic and faced outside Europe, so there are many potential international beneficiaries, although engagement will be less direct.

Wealth creation for UK and the Green Economy:
Improving shelf sea modeling capability has wider implications for many areas of the economy. Improved ecosystem predictions provide benefits for environmental impact assessments of marine renewable energy installations, and predictions of impacts of marine carbon capture and storage programmes. Improved bottom temperature predictions have potential benefits to demersal fisheries and gas pipeline planning criteria - both act within specific temperature tolerances. The move towards ocean-atmosphere coupled weather forecasting at the UK Met Office (UKMO) means this work potentially benefits UK weather forecasts, with agricultural, defense and tourism implications.

Media Relations and Public Engagement:
As opportunities arise, we will seek to present our research to UK and international audiences. We will publish at least one popular science article in Planet Earth and have an outward looking project website. In this way the general public will also have appropriate access to our research.