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, 129, e2023JC020743.
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 potentially
continuous trough‐scale 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 deep 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 the isopycnal layer of 26.6–27.3 kg/m3. It exhibits a characteristic speed of approximately O‐(1)
cm/s. Analyses and experiments suggest that the divergence of upwelling in the SCC layer (26.6–27.3 σ_θ
surface) gives rise to lateral potential vorticity transport, ultimately driving the deep cyclonic 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 in semi‐enclosed marginal seas.
Preprint (pdf)