Antarctic sea-ice loss shifts the Pacific Decadal Oscillation toward a positive phase

Antarctic sea-ice loss can influence climate far beyond the Southern
Hemisphere, but its remote impacts and underlying mechanisms remain
uncertain. Using two global climate models, we show that reduced Antarctic
sea ice triggers a positive Pacific Decadal Oscillation (PDO)–like
response, characterized by sea-surface temperature (SST) cooling in the
western North Pacific and warming in the eastern and subpolar Pacific.
This transient adjustment unfolds over timescales of up to ~20 years, with
the pace depending on the model. Mechanistically, this response is
initiated by a strengthened Indo-Atlantic cross-equatorial SST gradient,
reflecting enhanced off-equatorial Southern Hemisphere warming, that
drives a southward shift of the Asian jet. Idealized zonal-wind nudging
experiments confirm that this jet shift generates low sea-level pressure
anomalies over the western North Pacific. These anomalies intensify cold
oceanic advection from the subpolar region and reduce downward shortwave
radiation, producing SST cooling that contributes to the positive PDO-like
response. In quasi-equilibrium, the tropical Pacific shifts toward either
El Niño– or La Niña–like states, depending on the model and internal
variability. These findings imply that Antarctic sea-ice decline can act
as a cross-hemispheric driver, potential to shift the recent negative PDO
pattern toward a positive phase over the next decade.