Correlating ocean vertical transport and surface coherent structures

Vertical transport in the upper ocean impacts the transport of nutrients, surface mixing, and the ocean energy budget. Observing regions of significant vertical transport has proven to be difficult since vertical velocities in the ocean are often orders of magnitude smaller than horizontal velocities. What is available, however, is HF radar and satellite altimetry, which provide ocean surface velocities. While an Eulerian analysis of this field can yield some information, Lagrangian coherent structures prove to be more robust to noisy observational data. We correlate these structures on the surface to vertical transport below the surface. In particular, we compute the finite-time Lyapunov exponent (FTLE) field from just the surface velocity and compare this with the FTLE field for a full three-dimensional analysis and the corresponding vertical subduction. These correlations are tested on a high-fidelity simulation of a sheared submesoscale flow.