Shadowgraph profiles collected in the thermohaline staircase east of Barbados reveal nearly-horizontal banding—unlike the vertical banding that has been observed in other fingering-favorable parts of the ocean. A plausible interpretation of this optical microstructure is that vertical shear is tilting over fingers. This paper presents a model for shear-tilting of salt fingers. The Ri = 6 inertial wave shears observed in C-SALT would tilt over and damp out square planform (kx = ky) fingers so rapidly that they could not produce significant fluxes. Vertical sheets aligned with the shear (ky = 0) would behave like unsheared fingers if the shear was steady but oceanic shear is predominantly near-inertial so turns with time. Therefore, an across-sheet shear component will develop and initially-aligned sheets too will ultimately be tilted over. This happens slowly enough that sheets can grow to produce significant fluxes. When the growth of tilting sheets is limited by a critical inverse finger Richardson number, (∇ × V)2/N2 ∼ 3–16, the model produces microstructure and fluxes similar to those reported from C-SALT. However, this constraint does not explain the density ratio dependence in laboratory studies and numerical simulations. What constrains finger growth needs to be better understood.
Kunze, Eric. 1990. "The evolution of salt fingers in inertial wave shear." Journal of Marine Research 48, (3). https://elischolar.library.yale.edu/journal_of_marine_research/1977