Unveiling North Atlantic Deep Water pathways using nonlinear dynamics techniques

The Atlantic meridional overturning circulation, a cornerstone of the conveyor belt paradigm, is characterized by the large-scale poleward surface currents, the formation of deep water in the Norwegian, Greenland and Labrador seas and the equatorward deep water currents. This equatorward spread from high latitudes was expected to be largely contained along the Deep Western Boundary Current. Since the turn of this century, observations from moorings and Lagrangian floats within these water masses have defied this expectation. Instead, myriad interior pathways have been revealed across the North Atlantic.

Using surface trajectory data from the Global Drifter Program, along with deep trajectory data from the Argo Program, WOCE Subsurface Float Data Assembly Center, and OSNAP (Overturning in the Subpolar North Atlantic Program), a Markov-chain model representation of the surface and deep water dynamics in the North Atlantic is constructed. From a spectral analysis of its associated discrete transfer operator, we construct a quasi 3D Lagrangian geography formed by basins of attraction for time-asymptotic almost-invariant attracting sets. This enables an assessment of long-term fate of surface and deep waters as well as sources of deep water production. We also investigate preferred pathways of North Atlantic Deep Water using tools from transition path theory built on the constructed Markov chain.