Benthic storms are episodes of exceptionally strong near-bottom currents in the abyssal ocean. They contribute greatly to the bottom energy dissipation rate in the ocean and are important for sediment transport and biogeochemistry. Characterized by speeds > 20 cm/s lasting from 10 to 30 days at abyssal depths, they generally occur in areas with high surface eddy kinetic energy, such as in the North Atlantic underneath the Gulf Stream. Recurring benthic storms lead to the formation of bottom mixed layers (BMLs) and benthic nepheloid layers (BNLs, particle-rich layers extending several hundred meters above the seafloor). However, the dynamical mechanisms responsible for the occurrence of benthic storms are not well understood. Here, idealized experiments with an eddy-resolving model with high vertical resolution are conducted in order to address two questions: (i) Can the instability of a baroclinic, surface-intensified current induce near-bottom (4000 m) flows that are strong enough to produce benthic storms? (ii) Can these abyssal flows also lead to the formation of BMLs and BNLs?               

We find that, in all numerical experiments, a baroclinic, surface-intensified, rectilinear jet becomes unstable, meanders, and ultimately produces a complex eddy field. Initially, the meanders deepen and move eastward, i.e., in the same direction as the parent current but more slowly. Deep cyclones and anticyclones form all along the jet under the meander troughs and crests, as an integral component of the baroclinic instability. The pressure anomalies associated with the eddies extend over the whole water column, consistent with the tendency of flow barotropization in geostrophic turbulence, increasing kinetic energy near the bottom. Simultaneously, a BML develops, with thickness ranging from 40 m to 80 m depending on the experiment. Near-bottom currents underneath the surface eddying current can reach sustained speeds > 20 cm/s, comparable to those observed during benthic storms in the western North Atlantic. Converging motion near the bottom of deep cyclones leads to upward velocities of O(10 m/d), greater than the estimated settling speeds of a large fraction of fine sediment particles in this basin. Fluid particle trajectories suggest that fine sediment may be stirred up to 500 m above the bottom under the collective influence of deep cyclones and anticyclones, supporting the notion that surface current instability can also generate BNLs. Our study yields insight into the effects of upper ocean dynamics on near-bottom processes and calls for further research on vertical energy transfer in the ocean.