How does friction slow ocean currents near the seafloor?

Ocean currents are slowed near the seafloor primarily through the influence of boundary-layer friction, often referred to as bottom drag.12

This process occurs because the motionless ocean floor acts as a physical boundary that removes momentum from the circulating water. In fluid dynamics, friction arises when layers of fluid move at different velocities; a faster-moving layer is slowed by a slower-moving one through the transfer of kinetic energy, which is eventually dissipated as heat through turbulence. As currents flow along the ocean bottom, this interaction between the moving water and the stationary seafloor exerts a drag force that reduces the current's velocity. This effect is a critical factor in modeling the trajectory of currents, such as dense overflows descending along the continental slope.12