Abstract
The Kuroshio transports warm water in the Pacific poleward from the tropics and plays a crucial role in modulating surrounding climate. Based on independent data sets, we demonstrated that the Kuroshio weakened downstream east of Taiwan, but intensified upstream east of Luzon Island during 1993–2013. The surface velocity (volume transport) of the Kuroshio has decreased 12.5% (4~5%) off east Taiwan but increased 18% (8~18%) off east Luzon. The discordant upstream–downstream trend was attributable to changes in oceanic eddies and basin surface winds: greater (lesser) cyclonic eddies, lesser (greater) anticyclonic eddies, and positive (negative) tendency in the Pacific Basin wind curl contributed to a weakened (intensified) downstream (upstream) Kuroshio. The difference in water mass between the upstream and downstream Kuroshio was balanced by an anomalous eastward flow, the southern branch of the Subtropical Counter Current which was enhanced and evacuated the redundant water eastward into the Pacific.
Highlights
In the late 1990s, global climate shifted into a cold regime that ended in 2012–20131,2
During 1993–2013, multi-decadal discordant trends in surface velocity occurred along the Kuroshio, which were tied to changes in the Pacific basin wind stress curl (WSC) and mesoscale eddies: off east Taiwan, the weakened Kuroshio during 1993–2013 was attributed to the positive WSC trend and increased ratio of cyclonic/anticyclonic eddies in the latitude of eastern Taiwan
The Kuroshio acts as a conduit to transport warm water poleward, and the discordant trends affected this transport
Summary
During 1993–2013, multi-decadal discordant trends in surface velocity occurred along the Kuroshio (intensified upstream and weakened downstream), which were tied to changes in the Pacific basin WSC and mesoscale eddies: off east Taiwan (east Luzon), the weakened (intensified) Kuroshio during 1993–2013 was attributed to the positive (negative) WSC trend and increased (decreased) ratio of cyclonic/anticyclonic eddies in the latitude of eastern Taiwan (eastern Luzon). (1) Increased activity of cyclonic eddies and decreased activity of anticyclonic eddies contributed to a weakened downstream Kuroshio east of Taiwan. (2) A positive (negative) trend in the Pacific WSC north (south) of 20°N weakened (intensified) the downstream (upstream) Kuroshio east of Taiwan (east of Luzon Island). The decreasing SSH resulted from mesoscale eddies and the increase in SSH in the Pacific warm pool produced a northward pressure gradient during 1993–2013, which contributed to the strengthening eastward S-STCC
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