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The sea‐ice cover in the Barents and Kara Seas (BKS) displays pronounced interannual variability. Both atmospheric and oceanic drivers have been found to influence sea‐ice variability, but their relative strength and regional importance remain under debate. Here, we use the Liang‐Kleeman information flow method to quantify the causal influence of oceanic and atmospheric drivers on the annual sea‐ice cover in the BKS in the Community Earth System Model large ensemble and reanalysis. We find that atmospheric drivers dominate in the northern part, ocean heat transport dominates in the central and northeastern part, and local sea‐surface temperature dominates in the southern part. Furthermore, the large‐scale atmospheric circulation over the Nordic Seas drives ocean heat transport into the Barents Sea, which then influences sea ice. Under future sea‐ice retreat, the atmospheric drivers are expected to become more important. Plain Language Summary: The sea ice in the Barents and Kara Seas (BKS) is melting due to Arctic warming, but this is overlaid by large natural variability. This variability is caused by variations in the ocean and the atmosphere, but it is not clear which is more important in which parts of the region. We use a relatively new method that allows us to quantify cause‐effect relationships between sea ice and atmospheric and oceanic drivers. We find that in the north of the BKS, the atmosphere has the biggest impact, in the central and northeastern parts, it is the heat from the ocean, and in the south, it is the local sea temperature. We also find that wind patterns over the Nordic Seas affect how much oceanic heat comes into the Barents Sea, and that, in turn, affects the sea ice. Looking ahead, as the ice is expected to melt more in the future, the atmosphere is likely to become more important in driving sea ice variability in the BKS. This study helps us better understand how the ocean and atmosphere work together to influence the yearly changes in sea ice in this region. Key Points: Ocean heat transport drives sea‐ice variability in the central and northeastern Barents SeaAtmospheric temperature drives sea‐ice variability in the northern Barents‐Kara SeasAtmospheric circulation over the Nordic Seas drives ocean heat transport, which then influences sea‐ice variability [ABSTRACT FROM AUTHOR]

The Arctic sea-ice cover is strongly influenced by internal variability on decadal timescales, affecting both short-term trends and the timing of the first ice-free summer. Several mechanisms of variability have been proposed, but how these mechanisms manifest both spatially and temporally remains unclear. The relative contribution of internal variability to observed Arctic sea-ice changes also remains poorly quantified. Here, we use a novel technique called low-frequency component analysis to identify the dominant patterns of winter and summer decadal Arctic sea-ice variability in the satellite record. The identified patterns account for most of the observed regional sea-ice variability and trends, and they thus help to disentangle the role of forced and internal sea-ice changes over the satellite record. In particular, we identify a mode of decadal ocean–atmosphere–sea-ice variability, characterized by an anomalous atmospheric circulation over the central Arctic, that accounts for approximately 30 % of the accelerated decline in pan-Arctic summer sea-ice area between 2000 and 2012 but accounts for at most 10 % of the decline since 1979. For winter sea ice, we find that internal variability has dominated decadal trends in the Bering Sea but has contributed less to trends in the Barents and Kara seas. These results, which detail the first purely observation-based estimate of the contribution of internal variability to Arctic sea-ice trends, suggest a lower estimate of the contribution from internal variability than most model-based assessments. [ABSTRACT FROM AUTHOR]

The Arctic winter sea ice cover is in retreat overlaid by large internal variability. Changes to sea ice are driven by exchange of heat, momentum, and freshwater within and between the ocean and the atmosphere. Using a combination of observations and output from the Community Earth System Model Large Ensemble, we analyze and contrast present and future drivers of the regional winter sea ice cover. Consistent with observations and previous studies, we find that for the recent decades ocean heat transport though the Barents Sea and Bering Strait is a major source of sea ice variability in the Atlantic and Pacific sectors of the Arctic, respectively. Future projections show a gradually expanding footprint of Pacific and Atlantic inflows highlighting the importance of future Atlantification and Pacification of the Arctic Ocean. While the dominant hemispheric modes of winter atmospheric circulation are only weakly connected to the sea ice, we find distinct local atmospheric circulation patterns associated with present and future regional sea ice variability in the Atlantic and Pacific sectors, consistent with heat and moisture transport from lower latitudes. Even if the total freshwater input from rivers is projected to increase substantially, its influence on simulated sea ice is small in the context of internal variability. Significance Statement: The winter sea ice cover in the Arctic is declining due to global warming, but the decline is quite variable because of the chaotic nature of the climate system. We want to understand what causes this variability, both for the present and the next decades, and for different regions of the Arctic. We find that now and in the future, variability in the winter sea ice is influenced by transport of oceanic heat and atmospheric heat and moisture from the Pacific and Atlantic side of the Arctic. These findings improve our understanding of what influences changes in the winter sea ice cover, and could help to improve predictions of sea ice in the Arctic. [ABSTRACT FROM AUTHOR]