The North Atlantic subpolar gyre is a key region for the North Atlantic phytoplankton bloom (NAB), the foundation of the regional foodweb. The NAB is dependent on nutrients seasonally introduced into the surface ocean by deep winter convection. Under climate change, this pattern is threatened by increasing water column stratification, and the NAB may “collapse” as a result, representing a potential “tipping point” in the Earth system. We investigate change in winter mixing and the impacts on the SPG and the broader northern North Atlantic using 1. a spread of future projections from a low-resolution Earth system model (UKESM) and 2. a single, high-warming projection of a high-resolution ocean-only configuration of the same model (NEMO-MEDUSA). For both models we find significant declines in the strength of the NAB during the 21st century. In UKESM, this occurred across all projections, but with low spatiotemporal coherence. In NEMO-MEDUSA, changes in upper mixed layer depth, surface nutrients and chlorophyll concentrations were noticeably abrupt and more highly spatiotemporally-correlated. We also find a large (>30 day) phenological shift in the peak of the bloom aligned with the timing of this change, which may affect foodweb dynamics. Overall, defining “collapse” as a halving of surface chlorophyll, we find that the NAB collapses by the end of the century regardless of future projection. However, the timing, abruptness and coherence of this collapse differs in high and low resolution models, suggesting the need for higher resolution for prediction of abrupt and irreversible changes, especially those involving ecosystem dynamics.