Investigating Arctic Ocean Mixing and Heat Transport Using High-Resolution FESOM2 Simulation

The Arctic Ocean plays a significant role in amplifying regional climate warming, with ocean heat transport (OHT) and vertical mixing influencing surface temperature and sea-ice evolution. Yet, the pathways and timescales of heat redistribution remain poorly constrained due to limited observations and coarse model resolution. We employ simulations of the Finite-volumE Sea ice-Ocean Model version 2 (FESOM2) using coarse- and high-resolution meshes to investigate OHT and mixing conditions in the Arctic Ocean. Passive and idealised tracers are implemented in FESOM2 to evaluate the simulated circulation in the Arctic Ocean and to quantify water-mass mixing within the Inverse Gaussian Transit Time Distribution framework. The high-resolution FESOM2 substantially reduces tracer biases from the matching in-situ measurements compared to the coarse-resolution FESOM2 and other models, indicating improvements in the representation of mixing, advection pathways, and ventilation structures. High-resolution model results highlight distinct regional trends in the Arctic Ocean’s upper-ocean mixing and heat content during 1979–2018. Most of the Eurasian sector shows increased mixing and warming, thinning of the cold halocline, and pronounced sea-ice reduction. Conversely, the Canadian sector exhibits reduced mixing and heat content, halocline thickening, and weaker ice reduction. These contrasting patterns may indicate enhanced OHT from Atlantic and Pacific waters into the Eurasian upper-ocean layers, whereas the Canadian sector experiences comparatively limited heat penetration. These contrasting regional dynamics highlight the role of altered mixing driven by OHT in amplifying surface warming in the Eurasian sector, helping to explain why this region experiences faster surface warming compared to the Canadian sector.