Submesoscale Ocean Fronts and Turbulence (SOFT) observatory

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Ocean fronts separate waters of different temperatures and salinities over distances ranging from a few tens of kilometers down to hundreds of meters, a range called submesoscale. The ocean surface is populated with a convoluted web of submesoscale fronts, featuring rapid subsurface vertical velocities of 10 to 100 meters per day, an order of magnitude stronger than in the rest of the ocean. They may therefore play an important part in the exchange of heat and gases between the atmosphere and the ocean interior, and in the supply of nutrients to the sun-lit zone where photosynthesis takes place. However, computing performances will not be sufficient for the foreseeable future to resolve submesoscales in global ocean models. We must therefore develop parameterizations that realistically reproduce the collective effect of submesoscale processes on the resolved larger scales. Submesoscale-resolving numerical simulations are now being run in idealized or regional settings, but observations of submesoscale processes have remained sparse. The most detailed observations have been obtained from short-term ship-borne campaigns, due to the necessity of sampling the vertical and horizontal structure of the upper ocean at high resolution over extended areas. There is a lack of long-term continuous observations to provide a statistical view of submesoscale dynamics in a wide range of environmental conditions. One of the goals of this proposal is to start filling this observational void. As a first step, in the next five years, the Lower St-Lawrence Estuary will provide a natural laboratory to acquire long-term continuous observations of submesoscale processes, using high-frequency radars and moored vertical profilers. These observations are intended to guide the development of parameterizations of the cumulative effects of submesoscale on larger-scale processes, based on the simplest dynamics able to reproduce the main observed features.