Turbulent control of the physical structure of continental shelf seas
Large areas of our oceans undergo a seasonal cycle of stratification driven largely by the variable transfer of heat at the ocean surface balanced by contributions to ocean mixing from the wind and tides, with additional lesser contributions from surface waves and internal processes. Understanding the contribution that each of these processes makes to stratification and mixing is critical to understand and predict the physical structure of our seas so that the ocean contribution to global heat, momentum and carbon budgets can be determined. Gathering sufficient data on ocean turbulence and mixing processes to provide statistical certainty of such processes however, is difficult. The greatest uncertainties in the mixing conundrum are in the mid-water and upper ocean, where direct measurements are easily contaminated through interaction from ships and buoys and remote sensing methods from subsurface acoustic sensors is often out of range.
Ocean gliders have permitted a significant advance in the measurement of ocean turbulence in two ways 1) by enabling prolonged periods of measurements that were otherwise difficult and costly to achieve from ships and 2) by enabling these measurements to be extended to the near surface, where turbulent processes are traditionally under resolved. In this talk I will look at how these new data improve our understanding of how the balance between heating, convective and mixing mechanisms leads to the timing of spring stratification and the development and maintenance of physical structure in our shelf seas. These data show how the complex formation of multiple layers in the upper ocean can be largely described by the balance between wind mixing and solar heating, although some consideration is required from the mixing attributable to surface waves and internal mixing processes (such as internal waves) to balance the seasonal cycle.