Bottom Ekman transport drives transverse flows to shape contourite moat and drift systems

Abstract

Despite six decades of investigation into deepwater sedimentary systems, the mechanisms that generate transverse flows to transfer sediments across contourite channel (moat) and drift systems have remained unclear. Here we present the direct evidence of driving mechanisms from in situ observations of contourite systems, both deep marine (South China Sea) and lacustrine (Lake Champlain) environments. In these Northern Hemisphere locations, bottom Ekman transport (arising from the combined effects of the Coriolis force and bottom friction) drove leftward deflection of near-bottom currents (relative to the direction of the frictionless main flow above), resulting in transverse flows across the contourite moat–drift systems. In the Southern Hemisphere, current deflection would be to the right. These findings are relevant to any rotating planet or moon that harbors substantial liquid water, where these processes could produce bottom current (contourite) features — invaluable archives of past changes in oceanic circulation and climate, on Earth and elsewhere. One-Sentence Summary: In situ observations show that bottom Ekman transport can result in transverse flows across contourite moat–drift systems.