North Pacific Subtropical Mode Water Controlled by the Atlantic Multidecadal Variability

North Pacific Subtropical Mode Water (mode water hereafter) is a vertically homogeneous thermocline water mass, formed in the south of the Kuroshio Extension and occupying the whole subtropical Western Pacific Ocean. It transports mass, heat and nutrient from surface into subsurface ocean and provides memory of climate variability for climate prediction. Previous studies attributed decadal variability of the mode water to the Pacific Decadal Oscillation (PDO). Using available observations and reanalysis data, here we show that decadal to multi-decadal variability of the mode water mean temperature is controlled by the Atlantic Multi-Decadal Oscillation (AMO) rather than the PDO. During the AMO positive phase, warm sea surface temperature (SST) in the north Atlantic Ocean weakens the subtropical North Pacific westerlies by inducing anomalous easterlies in the subtropical west Pacific, which produce an enhanced northward Ekman transport of warm water into the Kuroshio Extension. This increases the mode water mean temperature through a subduction process and controls the upper-layer ocean heat content as well as the fish catches variability in the Northwestern Pacific. This mechanism is supported by a long-term pre-industrial model simulation and a pace-maker model experiment. Our finding suggests that the AMO is an important forcing of decadal climate and ecosystem variability and memory of prediction in the Kuroshio Extension region.