Deep Lagrangian connectivity in the global ocean inferred from Argo floats

The connectivity between ocean basins and sub-basin regions strongly influences the transport of ocean tracers and thus plays a role in regulating climate and ocean ecosystems. We describe the application of a new technique from nonlinear dynamical systems to infer the Lagrangian connectivity of the deep global ocean. We approximate the dynamic Laplacian using Argo trajectories from January 2011 to January 2017 and extract the eight dominant coherent (or dynamically self-connected) regions at 1500m depth. Our approach overcomes issues such as sparsity of observed data, and floats continually leaving and entering the dataset; only 10% of floats record continuously for the full six years. The identified coherent regions maximally trap water within them over the six-year time frame, providing a distinct analysis of the deep global ocean, and relevant information for planning future float deployment. A key result is that the coherent regions are highly stationary, showing minimal displacement over the six-year period. While our study is concerned with ocean circulation at a multi-year, global scale, the dynamic Laplacian approach may be applied at any temporal or spatial scale to identify coherent structures in ocean flow from positional time series information arising from observations or models.