This is the third cruise for the US Office of Naval Research’s Coherent Lagrangian Pathways from the Surface Ocean to Interior (Calypso) project.  The program is motivated by the understanding that the vertical movement of water from the surface to depth across the base of the mixed layer has implications for the transport of properties, gases, biogeochemistry, and the fate of drifting particles/objects. However, vertical velocities are weak (about a thousand times smaller than horizontal velocities) and difficult to detect. To represent these motions we need to answer the following questions: (1) How are water and properties from the surface boundary layer exported to depth?  (2) What coherent pathways act as conduits for exchange? (3) What dynamics shapes these pathways? (4) What are the Lagrangian trajectories? (5) What are the time and space scales of subduction? (6) Where does the water end up?  (7) Can we predict these pathways in 3 dimensions and what data are needed to aid or constrain predictive models?  Previous work has established the theoretical basis for predicting coherent Lagrangian structures in the ocean. Confirmation of the predictive theory has only been accomplished in the horizontal dimension and the observational study and confirmation of predictive theories for 3D plus time have not yet been demonstrated.

Calypso aims to: (1) Establish an understanding and predictive capability of the three-dimensional coherent pathways by which water carrying tracers and drifting objects is transported from the surface ocean to depths below the mixed layer. (2) Design and implement an observational study to test the theories, hypothesis, and predictions of the 3-D, time-evolving Lagrangian pathways.

Due to the need to sample across a range of scales, we have set up this two-ship study with numerous autonomous and Lagrangian platforms.  Eurofleets+ helped the observational program succeed via the award of ship time on R/V Pelagia.  During the cruise, most of the operations from R/V Pelagia focussed on repeat surveys at a front and a cyclonic eddy to the NE of the front with a variety of ship-based measurements and autonomous platforms.  Two-ship operations combined repeat small-scale surveys by R/V Pelagia , which were embedded within larger scale surveys by R/V Pourquois Pas.