Mean Currents on Bottom Slopes: A Semiglobal View

Abstract Currents in the deep ocean are infrequently measured and thus largely unknown. This paper analyzes the time-mean currents at the seafloor in high-resolution numerical simulations for the Atlantic basin, Pacific basin, and Indian Ocean Basin. The bottom speeds are largest on topographic slopes, and the geographical distribution of is complex, as is the variety of topographic shapes. Nevertheless, we identify and characterize representative regimes of bottom flow associated with wind-gyre western boundary currents, wind-driven boundary upwelling currents, thermohaline-forced deep western boundary currents, tidal residual currents, eddy-driven along-isobath (topostrophic) currents, mixing-driven abyssal upwelling currents, and ridge and canyon flows. The bottom currents are highly intermittent in their spatial statistics, but they are predominately prograde along-isobath currents and downhill across isobaths. Their statistics support the widespread occurrence of eddy-driven topostrophic flows with tidal rectification as an important secondary influence.