Fig. 4: The Lagrangian heat and salt divergence.

Zonally integrated Lagrangian heat (GW m−1; using equation (5)) and salt (kg s−1 m−1; derived from equation (7)) divergence of the Arctic outflows (a, b) and Atlantic inflows (c, d) that have exited the eastern Subpolar North Atlantic Ocean (SPNA) southward. The blue, black, and red line corresponds to total divergence, divergence below the mixed layer depth (MLD), and divergence within the MLD respectively. The magenta line shows the northern latitudinal limit ( ≈ 70 °N) within which we have employed the Eulerian surface watermass transformation framework. The cyan color indicates no divergence in heat and salt.