Stratification and mixing regimes in oceanic thin layers

Emily Shroyer¹

The vertical distribution of plankton is often marked by coherent patches with vertical scales of order one meter. The structure and maintenance of these layers can play an important role within the local ecosystem, potentially influencing predator behavior and foraging interactions. Here, I will detail measurements of thin layers observed over the New Jersey shelf in the summer of 2006. The observed layers were differentiated into two types based on their position in the water column, fluorescence intensity, and either community composition or cell condition. Both layer types were associated with stratification gradients, while the turbulent mixing environment for the two layer types differed significantly. Shallow layers were located in regions of relatively strong gradients and were exposed to strong mixing events within the surface mixed layer. Consequently, turbulent mixing of buoyancy and presumably nutrients may have been a key factor in maintaining shallow layers. In contrast, weak gradients and mixing indicate that turbulent processes may have been less critical for deep layers. This work highlights the need to understand the detailed statistics of mixing at time and vertical scales relevant to thin layers, more specifically the need to discern the time history of mixing of the fluid that composes layers.

¹College of Earth, Ocean and Atmospheric Sciences, OSU