North Pacific subtropical mode water, a vertically homogeneous thermocline water mass, occupies the entire subtropical Western Pacific Ocean. It transports mass, heat and nutrients from the surface to the subsurface ocean, providing memory of climate variability^{1,2,3,4,5,6,7,8,9,10,11}. Decadal variability of the mode water temperature has been attributed to the Pacific Decadal Oscillation (PDO)^2,3,12,13, but this is based on short data records. Here, using long records of observations, we show that decadal-to-multidecadal variability of the mode water mean temperature is instead controlled by the Atlantic Multidecadal Variability (AMV). During an AMV-positive phase, warm sea surface temperatures (SSTs) in the North Atlantic Ocean weaken the subtropical North Pacific westerlies; the associated anomalous easterlies in the subtropical west Pacific^4,5 drive a northward Ekman transport of warm water to the mode water formation area. Subduction of the warm water increases mode water temperature, influencing Northwestern Pacific upper ocean heat content and fish catches. A long pre-industrial model simulation with multiple AMV cycles and a pacemaker experiment support this mechanism—the AMV forcing alone can drive decadal variability of the mode water. Thus, the AMV provides important memory for prediction of decadal climate and ecosystem variability in the Pacific Ocean.

北太平洋副热带模态水是一种垂直均质的温跃层水团，占据整个副热带西太平洋。它将质量、热量和营养物质从地表输送到地下海洋，提供气候变化的记忆^{1,2,3,4,5,6,7,8,9,10,11}。模式水温的年代际变化归因于太平洋年代际振荡 (PDO) ^2,3,12,13，但这是基于短数据记录。在这里，使用长期的观察记录，我们表明模式水平均温度的年代际到年代际变率是由大西洋的年代际变率 (AMV) 控制的。在 AMV 阳性阶段，北大西洋温暖的海面温度 (SST) 削弱了副热带北太平洋西风带；副热带西太平洋相关的异常东风带^4,5将温水向北 Ekman 输送到模式水形成区域。暖水的俯冲增加了模态水温，影响了西北太平洋上层海洋的热量和鱼类捕捞量。具有多个 AMV 循环的长工业前模型模拟和起搏器实验支持这种机制——仅 AMV 强迫可以驱动模式水的年代际变化。因此，AMV 为预测太平洋的年代际气候和生态系统变率提供了重要的记忆。