Comprehensive Observational Features for the Kuroshio Transport Decreasing Trend During a Recent Global Warming Hiatus

• Published in: Geophysical research letters 2021-09, Vol.48 (18), p.n/a
• Main Authors: Liu, Zhao‐Jun, Zhu, Xiao‐Hua, Nakamura, Hirohiko, Nishina, Ayako, Wang, Min, Zheng, Hua
• Format: Article
• Language: English
• Subjects: Acoustic Doppler Current Profiler; Advection; Anomalies; Boundary currents; Climate change; Doppler sonar; dynamical topography; Geostrophy; Global warming; Height anomalies; Kuroshio; Latitude; Offshore; Propagation modes; Pycnocline; Pycnoclines; Sea surface; Shoaling; Straits; Subtropical circulation; Thermocline; Tokara Strait; Transport; Trapped waves; Trends; volume transport; Water masses; Wave propagation; Wind; Wind stress; Wind stress curl
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL094169

Linear trends in Kuroshio transport during a recent global warming hiatus (1998–2013) were evaluated using long‐term ferryboat ADCP (acoustic Doppler current profiler) data and tidal gauge data in the Tokara Strait south of Japan. The Kuroshio exhibited a remarkable weakening trend of approximately 0.05 Sv year−1 (1 Sv = 106 m3 s−1). The pycnocline in the weakened Kuroshio was relaxed and displayed shoaling at the offshore edge, which was attributed to vertical thermocline displacement rather than to water mass modification. Importantly, Kuroshio transport trends in the Tokara Strait were affected by sea surface height anomalies, which were driven by the combined effects of the clockwise baroclinic‐mode coastal trapped wave propagation along the southern coast of Japan and downstream Kuroshio advection in the East China Sea. Both features were induced by wind stress curl changes related to the global warming hiatus over the North Pacific. Plain Language Summary The Kuroshio is the western boundary current in the wind‐driven subtropical circulation of the North Pacific. It exits the East China Sea and flows into the North Pacific through the Tokara Strait between the Yakushima and Amami Oshima Islands to the south of Kyushu, Japan. This study revealed that the Kuroshio transport through the Tokara Strait showed a remarkable weakening trend along with a northward shift during 1998–2013. Changes in the wind stress curl in the high (low)‐latitude band over the North Pacific during the global warming hiatus exhibited negative (positive) tendencies, leading to anomalously high (low) sea surface heights. The high (low) sea surface height anomaly arrived at the onshore (offshore) side of Tokara Strait from the high (low)‐latitude band decreasing Kuroshio transport because of geostrophy. Key Points Kuroshio transport in the Tokara Strait south of Japan decreased by ∼4% during 1998–2013, indicating a rate of about 0.05 Sv year−1 Shoaling of the offshore pycnocline in the Kuroshio was due to vertical thermocline displacement rather than to modified water mass Dynamic‐topography propagation pathways from the northern and southern interior regions caused weakened Kuroshio transport in the hiatus