Cui, X., D. Yang, A. J. Miller, B. Yin and J. Yang, 2024:
Trough-scale slope countercurrent over the East China Sea shelf break driven
by upwelling divergence.
Journal of Geophysical Research-Oceans, sub judice.
Abstract.
Observations have revealed the existence of persistent slope countercurrents (SCCs) that
flow southwestward beneath the Kuroshio Current at several locations over the East China Sea
(ECS) continental slope. It was not clear whether these flows are localized circulation features or
segments of a trough-scale circulation system in the Okinawa Trough (OT). We demonstrate that
there indeed exists a continuous SCC along the ECS slope that is associated with an OT-wide
cyclonic circulation using high-resolution model simulations and physical interpretations. The
detailed features of the bottom OT circulation are illustrated by the trajectories of the Lagrangian
drifters and the time-varying distributions of passive tracers. The SCC in the ECS is
characterized by its weak yet persistent nature, typically located in narrow sloping regions at
depths ranging from 500 to 1000 meters. It exhibits a characteristic speed of approximately
O~(1) cm/s. Analyses and experiments suggest that the divergence of upwelling in the SCC
layer (500-1000 m) gives rise to lateral potential vorticity flux, ultimately driving the deep
oceanic OT circulation. Furthermore, the SCC also displays a substantial connection with the
onshore intrusion of the Kuroshio Current, particularly to the northeast of Taiwan Island. The
SCC may potentially play a crucial role in the transport of heat and nutrients, as well as in
regulating sediment distributions within the deep OT. This mechanism offers fresh insights into
explaining the presence of undercurrents beneath the western boundary currents in the global
ocean.
Preprint (pdf)