Wednesday, May 22, 2013
Environmental Science and Engineering Seminar
Turbulence, submesoscales, and phytoplankton blooms at ocean fronts
John R. Taylor, University Lecturer, Department of Applied Mathematics and Theoretical Physics, University of Cambridge
Fronts, or regions with sharp density contrasts, are ubiquitous features of the upper ocean. There are indications that ocean fronts play an important role in the coupled atmosphere/ocean climate system as hotspots for air/sea exchange and biological activity. Here, I will describe recent efforts to understand how dynamical processes influence the vertical structure and strength of ocean fronts and micro-organisms living in the frontal zone. In particular, I will discuss the competition between `submeoscale' frontal instabilities on scales of 1-10km, which act to increase the stable vertical density stratification, and turbulent mixing, which tends to homogenize the fluid. The balance between re-stratification and mixing can dramatically affect growth rates of phytoplankton, tiny free-floating algae. When nutrients are relatively abundant but light levels are low, a reduction in turbulent mixing rates caused by frontal re-stratification can trigger explosive phytoplankton growth events known as blooms. This mechanism helps to explain isolated blooms detected using remote sensing, and may represent an important source of unresolved variability in global biogeochemical models.