The stratosphere is connected to tropospheric weather and
climate. In particular, extreme stratospheric circulation events are known to
exert a dynamical feedback on the troposphere1. However, it is unclear whether
the state of the stratosphere also affects the ocean and its circulation. A
co-variability of decadal stratospheric flow variations and conditions in the
North Atlantic Ocean has been suggested, but such findings are based on short
simulations with only one climate model2. Here we assess ocean reanalysis data
and find that, over the previous 30 years, the stratosphere and the Atlantic
thermohaline circulation experienced low-frequency variations that were similar
to each other. Using climate models, we demonstrate that this similarity is
consistent with the hypothesis that variations in the sequence of stratospheric
circulation anomalies, combined with the persistence of individual anomalies,
significantly affect the North Atlantic Ocean. Our analyses identify a
previously unknown source for decadal climate variability and suggest that
simulations of deep layers of the atmosphere and the ocean are needed for
realistic predictions of climate.