Evaluation of sea ice variability in three ocean reanalyses and two regional models in the Barents and Kara Seas in 1991–2020

Satellite measurements indicate that the Barents and Kara Seas have experienced some of the most significant sea ice declines and increases in sea surface temperature in the Arctic. Understanding the processes driving these changes is of utmost importance to assess the implications of climate change in the Arctic and globally. Given the observational limitations in these high-latitude areas, coupled models and reanalysis products play a key role. However, it is essential to determine how reliably these products represent the observed sea ice decline and mixed-layer warming. Models are often evaluated on a pan-Arctic scale, but the model skill might differ when considering sub-regions. This study examines two coupled regional climate models (HIRHAM–NAOSIM 2.2 and RASM), two regional ocean reanalyses (RARE 1.15.2 and TOPAZ 4B), one global ocean reanalysis (ORAS5), and OSI SAF satellite observations over the period 1991–2020. We focus on spring (March–May) and autumn (August–October) sea ice area and sea ice concentration, the edge of the sea ice, and the temperature of the mixed layer. We also examine correlations between sea ice and mixed-layer temperature anomalies and five climate indices to assess how the datasets respond to large-scale climate variability. The results show a statistically significant decrease in sea ice area and sea ice concentration in the satellite measurements and in all reanalyses. However, HIRHAM–NAOSIM shows only a near-significant decline in the Barents Sea, RASM shows no long-term change, and none of the two models shows a significant trend in the Kara Sea. Additionally, the reanalyses show a more pronounced warming of the mixed layer than the coupled models, particularly in autumn and in the Kara Sea. ORAS5 and TOPAZ agree most closely with the observed sea ice, partly because assimilated observations constrain their historical states, whereas RARE reproduces the decreasing trends but overestimates sea ice and shows anomalous mixed-layer temperature behaviour in the Barents Sea. The reanalyses also represent the relationships with the climate indices more consistently than the coupled models, particularly for the Atlantic Multidecadal Oscillation and the Northern Hemisphere ocean heat content. Among the coupled models, HIRHAM–NAOSIM represents changes in the Barents Sea better than RASM, but in the Kara Sea, where none of the models captures the decreasing trends, RASM has a more realistic mean sea-ice state. Although the coupled models reproduce interannual variability, the results indicate that in particular the effects of large-scale changes of the ocean circulation are not realistically reproduced in the coupled models.