This study aims to investigate variability of the deep South China Sea (SCS) circulation using the Hybrid Coordinate Ocean Model (HYCOM) global reanalysis product. The results reveal that annual cycle is a dominant component in the deep SCS circulation. Meanwhile, the boundary circulation strength is the weakest in January and peaks between June and September. The eastern and southern boundary currents strengthen/weaken one to three months earlier than that in the western and northern boundaries. Vector Empirical Orthogonal Functions (VEOF) analysis results reveal that semiannual and intraseasonal fluctuations are significant components, of which the spatial patterns are mainly confined in the northern and western boundary areas as well as the southwestern sub-basin. Wavelet analysis results show the strength of significant fluctuation varies year to year. Trend analysis results indicate a decadal weakening in the deep SCS circulation. An anomalous anticyclonic circulation, 50–70 km apart from the slope break, tends to weaken the cyclonic boundary circulation in the western and northern boundaries as well as the southwestern sub-basin. This trend is similar to the observed decadal weakening in the North Atlantic deep circulation. Thus, the findings of this study reveal that the variation of the deep SCS circulation has a remarkable response to the climate change. The mechanisms responsible for the variation are worth pursuing if more observations are available.

Yaohua Zhu;Guojiao Cao;Yonggang Wang;Shujiang Li;Tengfei Xu;Dingqi Wang;Fei Teng;Zexun Wei

First Institute of Oceanography,and Key Laboratory of Marine Science and Numerical Modeling,Ministry of Natural Resources,Qingdao 266061,China;Laboratory for Regional Oceanography and Numerical Modeling,Pilot National Laboratory for Marine Science and Technology(Qingdao),Qingdao 266237,China;Shandong Key Laboratory of Marine Science and Numerical Modeling,Qingdao 266061,China;Navigation College,Jiangsu Maritime Institute,Nanjing 211100,China;College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao 266100, China

海洋学报（英文版）

[1]Yaohua Zhu;Guojiao Cao;Yonggang Wang;Shujiang Li;Tengfei Xu;Dingqi Wang;Fei Teng;Zexun Wei-.Variability of the deep South China Sea circulation derived from HYCOM reanalysis data)[J].海洋学报（英文版）,2022(07):54-64

VEOF,semiannual

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