Diagram showing the proposed mechanism of the weakening of the Ryukyu Current.
Schematic of the proposed mechanism of the weakening of the Ryukyu Current from 1993 to 2018. The gray 3D surface shows the bathymetry. The color section plots indicate the trends of the current from Taiwan to Amamioshima (blue: decrease, red: increase), and the black contours show the mean velocity during this period. Blue arrows in 3 sections indicate the onshoreward shifts of the Ryukyu Current axis. The orange arrows show the typical paths of the Kuroshio and Ryukyu Currents. Kerama Gap (KG) and Tokara Strait (TK) are labeled. Inset denotes the vertical section across the Ryukyu Current. Black line indicates the density surface. The up and down arrows indicate the shoaling and deepening of the density layer, respectively. Credit: Liu et al. [2022], Figure 8
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Journal of Geophysical Research: Oceans

Many ocean currents are found to be strengthened by global warming. However, recent studies point out that there was a hiatus in warming that is considered have slowed down the Kuroshio in the East China Sea.

The Ryukyu Current is a unique western boundary current of the North Pacific accompanied by the subsurface velocity maxima, which flows northeastward off the eastern coast of Ryukyu Island chain and merges into the Kuroshio, south of the Japanese island of Kyushu.

Using ocean reanalysis data, Liu et al. [2022] found that the Ryukyu Current also slowed down during a 1993-2018 global warming hiatus. Their results also suggest that signals of the weakened Kuroshio in the Tokara Strait and that of the Kerama Gap overflow propagate southward along the eastern coast of Ryukyu Island chain as topographic Rossby waves, leading to the shoaling of density layers on the shore side. Further, the increased number of westward traveling anticyclonic eddies propagating into the regions uplifted density layers on the offshore side. These combined effects are found to be responsible for the weakening of the Ryukyu Current.

Citation: Liu, Z.-J., Zhu, X.-H., Nakamura, H., Wang, M., Nishina, A., Qiao, Y.-X., & Zhu, Z.-N. (2022). Response of the Ryukyu Current to climate change during 1993–2018: Is there a robust trend? Journal of Geophysical Research: Oceans, 127, e2022JC018957. https://doi.org/10.1029/2022JC018957

—Takeyoshi Nagai, Editor, JGR: Oceans

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