Abstract
<jats:p>The northwest Atlantic shelf is one of the fastest-warming ocean regions on Earth, yet the cause of the warming has remained ambiguous between local atmospheric forcing and ocean heat advection. Combining satellite sea-surface temperature (1982&ndash;2025), the GLORYS12V1 reanalysis (1993&ndash;2024), atmospheric reanalyses, and in-situ hydrography, we show that the Mid-Atlantic Bight shelfbreak and Slope Sea warmed at 0.35&ndash;0.5 &deg;C per decade, driven mainly by ocean heat advection. Three independent pieces of evidence rule out local atmospheric forcing: the net air&ndash;sea heat-flux trend is flat in two atmospheric reanalyses, the warming is subsurface-intensified (peaking near 47 m), and it maximizes outside the cold season. In the GLORYS12V1 reanalysis, the Gulf Stream north wall migrated northward (+0.10&deg; lat (6 NM) per decade), the jet at Cape Hatteras grew warmer, saltier, and stronger (+0.14 PW per decade heat transport), and warm, salty Atlantic Temperate Slope Water occupied the Gulf of Maine inflow (+0.67 &deg;C per decade at ~150 m) as cold, fresh Labrador Slope Water retreated. A daily-resolved heat budget shows the advective heat supply repartitioning, with mean-flow heat convergence strengthening as transient-eddy convergence declines. Measuring the polar source by water-mass volume rather than temperature resolves an apparent paradox: the two sources oppose one another interannually yet warm the shelf together on the decadal scale. The thermodynamic signature of this mechanism is reproduced across independent products and in-situ observations, and the Gulf Stream strengthening is corroborated by an independent satellite-altimetry proxy; the velocity-based transport magnitudes remain those of a single eddy-permitting reanalysis.</jats:p>