Atlantification drives recent strengthening of the Arctic overturning circulation.

The Arctic Ocean is the northern terminus of the Atlantic Meridional Overturning Circulation (AMOC), whose dense water masses are key to the global ocean circulation. The Arctic climate is rapidly changing, and it is not known how the Arctic Ocean overturning circulation is responding. Here, we use a high-resolution ocean reanalysis, corroborated by observations, to show that a poleward expansion of warm Atlantic waters and corresponding sea-ice loss, a phenomenon referred to as an "Atlantification" of the Arctic, has caused a poleward shift of the dense water source regions in recent decades (1993-2020). This is manifested in enhanced surface water mass transformation in the Arctic Ocean, compensating for a reduction in the Nordic Seas. The associated strengthening of the Arctic Ocean overturning circulation has ensured that the transport of dense overflow waters across the Greenland-Scotland Ridge to the AMOC's lower limb has remained stable. Our results thus provide evidence for a resilient northern overturning circulation in a warming climate.