Abstract
Based on satellite and analysis data and in situ observations acquired during May 23, 2017 to May 19, 2018, the spatiotemporal variations of the along-slope counter-flow off northeastern Taiwan were investigated. It was observed that the along-slope counter-flow in the subsurface layer was uplifted and lowered significantly during the study period. The counter-flow was significantly uplifted (lowered) while the sea surface was during an interval of positive (negative) geostrophic velocity anomaly (GVA) curl. The vertical migration of the counter-flow was also found closely linked with the Kuroshio intrusion (KI) to the northeast of Taiwan. The depths of both the upper boundary and the axis of the counter-flow were found proportional to the KI variance along the western continental slope off northeastern Taiwan. More importantly, it was established that the variation of the KI to the northeast of Taiwan had better correlation with the counter-flow than the Kuroshio derived from altimetry data. Thus, further study of the variation and mechanism of the along-slope counter-flow is needed to improve the understanding and prediction of the KI in the area of northeastern Taiwan, as well as the biochemical systems and marine economy in the East China Sea in the future.
Highlights
The Kuroshio is the strongest western boundary current in the Pacific Ocean, transporting warm, salty and nutrient-rich water from the seas off eastern Philippines northward to the seas off eastern Japan [1,2]
The depth of the bottom of the counter-flow at the in situ observation sites was deeper than the depth of the deployed acoustic Doppler current profiler (ADCP) and it could not be determined in this study
The depths of the upper boundary and axis of the counter-flow rose during the summer months (May–October) and fell during the winter months (November–April); the transition times were at the end of April and at the end of October (Figure 3)
Summary
The Kuroshio is the strongest western boundary current in the Pacific Ocean, transporting warm, salty and nutrient-rich water from the seas off eastern Philippines northward to the seas off eastern Japan [1,2]. The Kuroshio has significant influence on the marginal seas, atmosphere and climate while traveling northward along the continental shelf west of the Pacific Ocean [3,4,5,6,7]. It is a unique and significant phenomenon that the Kuroshio current intrudes onto the East China Sea shelf off northeastern Taiwan [5,8,9,10]. Despite the northward-flowing Kuroshio water, a unique along-slope counter-flow exists in the subsurface layer below the depth of 150 m [21,22].
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