Intensified currents associated with benthic storms underneath an eddying jet

Figure provided by Sean Chen

Benthic storms are episodes of intensified near‐bottom currents capable of sediment resuspension in the deep ocean. They typically occur under regions of high surface eddy kinetic energy (EKE), such as the Gulf Stream. Although they have long been observed, the mechanisms responsible for their formation remain poorly understood. In this study, we use an ocean circulation model to simulate the baroclinic instability of a surface current like the Gulf Stream, and to explore the effects of this instability on the abyssal flows near the bottom in an idealized zonal channel (panel a: domain and initial condition). We find that the unstable surface-intensified jet develops meanders and evolves into alternating, deep‐reaching cyclones and anticyclones (panel b, i-ii: normalized relative vorticity near surface and bottom, respectively). Simultaneously, EKE increases near the bottom due to the convergence of vertical eddy pressure fluxes, leading to near‐bottom currents comparable to those observed during benthic storms (panel b, iii: vertical section of EKE). The intensity of deep currents varies strongly with distance from the bottom, which creates turbulence and a well‐mixed layer adjacent to the deep seabed. In deep cyclones, particles from near the bottom can be transported upward through the entire well‐mixed layer (panel c, i-iv: initial particle positions; lateral particle distribution after 30 days; vertical distribution of particles after 30 days). Overall, our study shows that the physical environment near the bottom may exhibit a strong response to the instability of surface currents, which may have a potentially significant impact on the transport of fine sediment from the seafloor.