Towards understanding of future Arctic Ocean using high-resolution FESOM2 model

The Arctic Ocean is currently experiencing some of the most rapid, complex, and far-reaching climatic transformations on Earth. These changes are driven by intensified global warming and manifest through a combination of diminishing sea ice, altered ocean circulation, and shifting atmospheric interactions. Despite the Arctic's central role in regulating planetary climate feedbacks, most global climate models still lack the spatial resolution required to adequately represent mesoscale eddies. These eddies, which are typically on the scale of a few to tens of kilometres, are critical for capturing key processes such as lateral heat transport, vertical mixing, and the redistribution of tracers and momentum. Their influence is particularly pronounced in the Arctic, where steep gradients in temperature and salinity, along with seasonal sea-ice variability, create an environment highly susceptible to small-scale dynamical features. In this study, we apply a next-generation global sea ice–ocean model configured with kilometre-scale horizontal resolution, specifically optimized for high-latitude processes, to investigate how Arctic eddy activity responds under conditions of sustained warming. Our findings show that in a world that has warmed by 4 degrees Celsius, the average eddy kinetic energy increases significantly, approximately tripling relative to present-day levels. This robust increase is primarily attributed to stronger baroclinic instability, which arises due to intensified lateral density gradients and extensive sea-ice retreat. Beyond this energetic amplification, the simulations reveal notable structural changes in eddy distribution across depth layers. While the number of eddies in mid-to-deep waters decreases, those that remain tend to become larger in size, suggesting that energy is concentrated into fewer but more vigorous features. At the same time, the upper ocean experiences a sharp rise in the number and strength of near-surface eddies, driven by increased wind forcing and surface buoyancy fluxes in newly ice-free regions. Recognizing the essential role of mesoscale eddies in Arctic circulation and vertical heat exchange, we further examine how these evolving patterns affect sea-ice seasonality. Our analysis indicates that under accelerated warming, the probability of predominantly ice-free Arctic summers becomes considerably higher. A direct comparison between eddy-rich and eddy-present model configurations demonstrates that the higher-resolution configuration, which explicitly resolves mesoscale processes, produces a significantly extended open-water season by the end of the century. This extension is closely associated with enhanced upper-ocean vertical mixing, which results from elevated shear and weakened stratification linked to the intensification of near-surface eddies. Consequently, summer sea-ice melting begins earlier, while autumn freeze-up is delayed, revealing the high sensitivity of sea-ice regimes to fine-scale ocean dynamics. Taken together, these findings highlight the intricate and interconnected mechanisms by which the Arctic climate system responds to external forcing. From the substantial increase in eddy kinetic energy and the enlargement of deep eddy structures, to the intensification of surface eddy activity and the shift in sea-ice timing, our study underscores the importance of high-resolution ocean modeling in capturing these critical dynamics. In addition to its implications for sea-ice extent, enhanced eddy-driven mixing has broader consequences for marine heatwave development, nutrient cycling, and primary productivity, thereby influencing biodiversity and ecosystem resilience. Moreover, by shedding light on the interactions between mesoscale eddies and large-scale oceanic and atmospheric circulation patterns, our results provide an essential scientific basis for improving future projections of Arctic environmental change. To fully understand and predict the impacts of these evolving processes, we recommend a coordinated research effort that combines high-resolution modeling with comprehensive observational strategies. These should include advanced satellite measurements, expanded autonomous observing platforms, and targeted field campaigns designed to resolve fine-scale variability in ocean and ice dynamics. Such integrated approaches are vital for capturing the full spectrum of mesoscale influences on the Arctic system and for assessing their implications within the broader context of Earth system change.