The Weakened Upwelling at the Upstream Kuroshio in the East China Sea Induced Extensive Sea Surface Warming

The interannual sea surface temperature trend of the Kuroshio in the East China Sea (ECS‐Kuroshio) is significantly different from that of the ECS‐shelf region. Based on 33 years (1982–2014) of observational temperature data in the ECS, the upstream ECS‐Kuroshio, as an upwelling region, shows an opposite temperature trend to the downstream ECS‐Kuroshio, creating a horizontal “dipole” structure. Vertical heat transport modulated by upwelling variability in the upstream ECS‐Kuroshio can be the main factor for the distinct temperature trend in the upstream ECS‐Kuroshio. This upstream trend can expand to downstream areas through horizontal advections. As a result, the weakened upwelling triggered a significant warming trend in the entire upper layer of the ECS‐Kuroshio during the warming period (1999–2014). The weakening trend of upwelling and global rewarming conditions may lead to robust warming in the Kuroshio region in the middle of this century. Plain Language Summary The trend of sea surface temperature (SST) is used as a climate change indicator over global areas. The recent temperature trend in the Kuroshio can be separated into three stages, namely, the cooling period (1982–1998), the warming period (1999–2014) and the rapid warming period (2014‐present). However, the SST trend in the Kuroshio region in the East China Sea (ECS‐Kuroshio) was much weaker or even opposite to that in the ECS‐shelf, which means that different mechanisms may act strongly on this western boundary current area. Based on 33 years (1982–2014) of three‐dimensional observational data, this study investigated an opposite temperature trend in the ECS‐Kuroshio region in comparison with the global temperature trend. Furthermore, a “dipole” structure of temperature trends between the upstream and downstream of the ECS‐Kuroshio occurred during both periods. The upwelling variability in the upstream ECS‐Kuroshio region, which varies with the intensity of the ECS‐Kuroshio, is responsible for the opposite variability and “dipole” structure of temperature trends. A wider area was affected by weakened upwelling than was affected by strong upwelling, indicating that a weakening Kuroshio can be more sensitive to the climate system and may affect robust warming in the future. Key Points The interannual temperature trend upstream of the Kuroshio in the East China Sea (ECS) is opposite to the trend of the adjacent shelf The trends upstream and downstream of the Kuroshio also show opposite signs,