Re-emergence memory of subtropical mode-water links Atlantic and Pacific multidecadal variability.

Understanding how the ocean provides the memory for maintaining decadal to multidecadal variability is key to climate prediction. An important question is what process could provide the observed significant time lag between the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO). Here, we show that the Pacific Ocean could store climate anomalies within the subtropical recirculation gyre for a decadal duration, providing a 'seeding' link between the AMO and the PDO. The AMO-induced multidecadal temperature anomalies in the Northwestern Pacific Ocean are subducted into the thermocline and sequestered in the North Pacific Subtropical Mode Water. These temperature anomalies propagate along the recirculation gyre and eventually rejoin the Kuroshio one decade later. Once re-emerged in the Kuroshio-Oyashio Extension region, the anomalies may engage with local air-sea feedback, triggering the PDO. Our findings demonstrate that the mode water could provide a much-needed ocean memory for the prediction of multidecadal variability.