Notes on Bower et al. (2009; Nature)

Summary

In this paper, using (Lagrangian) RAFOS floats and floats from a numerical simulation, the authors argue that, contradictory to the traditional picture, most of the recently-formed Labrador Sea Water does not flow continuously within the Deep Western Boundary Current (DWBC) but follows an interior pathway, recirculating into the subpolar gyre and crossing beneath the Gulf Stream into the subtropical gyre. This interior pathway is, furthermore, turbulent and eddy-driven (see Lozier 1997, Lozier 1999).

The interruption of the DWBC is located between 42N (Tail of the Grand Banks) and 45N (Flemish Cap). South of these latitudes, the water flowing within the DWBC “in the subtropical basin is mainly transporting waters that are recirculating north of the Gulf Stream and west of the Grand Banks in the Northern Recirculation Gyre”.

Notes

• Only 8% of the floats (3 over 40 floats) followed the DWBC.
• One possible cause for the interruption of the DWBC is the North Atlantic Current (NAC) when flow closer to the coast.
• Using “e-floats” launched in a numerical simulation, it is found that only after 10 years, some floats re-enter the DWBC from the subpolar gyre to be advected southward, thus “emphasizing the importance of recirculation in the Newfoundland Basin in slowing the equatorward transport of recently ventilated LSW in the DWBC”.
• The interior circulation from the subpolar to the subtropical gyre is eddy-driven: see Lozier (1997) and Lozier (1999).

References

• Bower, A. S. et al. (2009) : Interior pathways of the North Atlantic meridional overturning circulation. Nature 459, 243-247.
• Lozier, M. S. (1997) : Evidence for large-scale eddy-driven gyres in the North Atlantic. Science 277, 361–364.
• Lozier, M. S. (1999) : The impact of mid-depth recirculations on the distribution of tracers in the North Atlantic. Geophys. Res. Lett. 26, 219–222.