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1. Western North Pacific influences on the interannual to decadal variability of Barents-Kara Sea ice during spring

   https://doi.org/10.1126/sciadv.ady7939  

   Cao, Shutao; Duan, Anmin; Dai, Aiguo; Zhang, Chao; Zhang, Ping; Peng, Yuzhuo; Mao, Qi (December 2025, Science Advances)

   Spring sea ice cover in the Barents-Kara Seas (BKS) exhibits notable interannual to decadal variability with spatial patterns distinct from winter. While previous studies suggest that internal climate variability dominates, the specific drivers remain to be identified. Using observations and model simulations, we reveal that atmospheric teleconnection from the western North Pacific accounts for ~26 to 40% of the interannual to decadal variability of the BKS sea ice during February-March-April. A poleward-propagating Rossby wave train, forced by divergent winds associated with the Western Pacific (WP) pattern, links WP to BKS sea ice variability by inducing lower-atmospheric circulation anomalies over the North Atlantic that enhance poleward heat and moisture transport. Furthermore, decadal shifts in the WP pattern, potentially originating from the Pacific Decadal Oscillation, have modulated the sea ice trend over the BKS, driving accelerated retreat in the 2000s and a slowdown after 2015. A projected transition of WP to its negative phase may accelerate BKS sea ice loss in the coming decade. 

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2. Origins of Barents-Kara sea-ice interannual variability modulated by the Atlantic pathway of El Niño–Southern Oscillation

   https://doi.org/10.1038/s41467-023-36136-5  

   Luo, Binhe; Luo, Dehai; Ge, Yao; Dai, Aiguo; Wang, Lin; Simmonds, Ian; Xiao, Cunde; Wu, Lixin; Yao, Yao (December 2023, Nature Communications)

   Abstract Winter Arctic sea-ice concentration (SIC) decline plays an important role in Arctic amplification which, in turn, influences Arctic ecosystems, midlatitude weather and climate. SIC over the Barents-Kara Seas (BKS) shows large interannual variations, whose origin is still unclear. Here we find that interannual variations in winter BKS SIC have significantly strengthened in recent decades likely due to increased amplitudes of the El Niño-Southern Oscillation (ENSO) in a warming climate. La Niña leads to enhanced Atlantic Hadley cell and a positive phase North Atlantic Oscillation-like anomaly pattern, together with concurring Ural blocking, that transports Atlantic ocean heat and atmospheric moisture toward the BKS and promotes sea-ice melting via intensified surface warming. The reverse is seen during El Niño which leads to weakened Atlantic poleward transport and an increase in the BKS SIC. Thus, interannual variability of the BKS SIC partly originates from ENSO via the Atlantic pathway. 

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3. Mooring Observations of Air–Sea Heat Fluxes in Two Subantarctic Mode Water Formation Regions

   https://doi.org/10.1175/JCLI-D-19-0653.1  

   Tamsitt, Veronica; Cerovečki, Ivana; Josey, Simon A.; Gille, Sarah T.; Schulz, Eric (April 2020, Journal of Climate)

   Wintertime surface ocean heat loss is the key process driving the formation of Subantarctic Mode Water (SAMW), but there are few direct observations of heat fluxes, particularly during winter. The Ocean Observatories Initiative (OOI) Southern Ocean mooring in the southeast Pacific Ocean and the Southern Ocean Flux Station (SOFS) in the southeast Indian Ocean provide the first concurrent, multiyear time series of air–sea fluxes in the Southern Ocean from two key SAMW formation regions. In this work we compare drivers of wintertime heat loss and SAMW formation by comparing air–sea fluxes and mixed layers at these two mooring locations. A gridded Argo product and the ERA5 reanalysis product provide temporal and spatial context for the mooring observations. Turbulent ocean heat loss is on average 1.5 times larger in the southeast Indian (SOFS) than in the southeast Pacific (OOI), with stronger extreme heat flux events in the southeast Indian leading to larger cumulative winter ocean heat loss. Turbulent heat loss events in the southeast Indian (SOFS) occur in two atmospheric regimes (cold air from the south or dry air circulating via the north), while heat loss events in the southeast Pacific (OOI) occur in a single atmospheric regime (cold air from the south). On interannual time scales, wintertime anomalies in net heat flux and mixed layer depth (MLD) are often correlated at the two sites, particularly when wintertime MLDs are anomalously deep. This relationship is part of a larger basin-scale zonal dipole in heat flux and MLD anomalies present in both the Indian and Pacific basins, associated with anomalous meridional atmospheric circulation. 

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4. Physical Links from Atmospheric Circulation Patterns to Barents–Kara Sea Ice Variability from Synoptic to Seasonal Timescales in the Cold Season

   https://doi.org/10.1175/JCLI-D-23-0155.1  

   Yu Feng Siew, Peter; Wu, Yutian; Ting, Mingfang; Zheng, Cheng; Clancy, Robin; Kurtz, Nathan T.; Seager, Richard (November 2023, Journal of Climate)

   Abstract Previous findings show that large-scale atmospheric circulation plays an important role in driving Arctic sea ice variability from synoptic to seasonal time scales. While some circulation patterns responsible for Barents–Kara sea ice changes have been identified in previous works, the most important patterns and the role of their persistence remain unclear. Our study uses self-organizing maps to identify nine high-latitude circulation patterns responsible for day-to-day Barents–Kara sea ice changes. Circulation patterns with a high pressure center over the Urals (Scandinavia) and a low pressure center over Iceland (Greenland) are found to be the most important for Barents–Kara sea ice loss. Their opposite-phase counterparts are found to be the most important for sea ice growth. The persistence of these circulation patterns helps explain sea ice variability from synoptic to seasonal time scales. We further use sea ice models forced by observed atmospheric fields (including the surface circulation and temperature) to reproduce observed sea ice variability and diagnose the role of atmosphere-driven thermodynamic and dynamic processes. Results show that thermodynamic and dynamic processes similarly contribute to Barents–Kara sea ice concentration changes on synoptic time scales via circulation. On seasonal time scales, thermodynamic processes seem to play a stronger role than dynamic processes. Overall, our study highlights the importance of large-scale atmospheric circulation, its persistence, and varying physical processes in shaping sea ice variability across multiple time scales, which has implications for seasonal sea ice prediction. Significance StatementUnderstanding what processes lead to Arctic sea ice changes is important due to their significant impacts on the ecosystem, weather, and shipping, and hence our society. A well-known process that causes sea ice changes is atmospheric circulation variability. We further pin down what circulation patterns and underlying mechanisms matter. We identify multiple circulation patterns responsible for sea ice loss and growth to different extents. We find that the circulation can cause sea ice loss by mechanically pushing sea ice northward and bringing warm and moist air to melt sea ice. The two processes are similarly important. Our study advances understanding of the Arctic sea ice variability with important implications for Arctic sea ice prediction. 

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5. Wintertime extreme warming events in the high Arctic: characteristics, drivers, trends, and the role of atmospheric rivers

   https://doi.org/10.5194/acp-24-4451-2024  

   Ma, Weiming; Wang, Hailong; Chen, Gang; Qian, Yun; Baxter, Ian; Huo, Yiling; Seefeldt, Mark W (January 2024, Atmospheric Chemistry and Physics)

   Abstract. An extreme warming event near the North Pole, with 2 m temperature rising above 0 °C, was observed in late December 2015. This specific event has been attributed to cyclones and their associated moisture intrusions. However, little is known about the characteristics and drivers of similar events in the historical record. Here, using data from European Centre for Medium-Range Weather Forecasts Reanalysis, version 5 (ERA5), we study these winter extreme warming events with 2 m temperature over a grid point above 0 °C over the high Arctic (poleward of 80° N) that occurred during 1980–2021. In ERA5, such wintertime extreme warming events can only be found over the Atlantic sector. They occur rarely over many grid points, with a total absence during some winters. Furthermore, even when occurring, they tend to be short-lived, with the majority of the events lasting for less than a day. By examining their surface energy budget, we found that these events transition with increasing latitude from a regime dominated by turbulent heat flux into the one dominated by downward longwave radiation. Positive sea level pressure anomalies which resemble blocking over northern Eurasia are identified as a key ingredient in driving these events, as they can effectively deflect the eastward propagating cyclones poleward, leading to intense moisture and heat intrusions into the high Arctic. Using an atmospheric river (AR) detection algorithm, the roles of ARs in contributing to the occurrence of these extreme warming events defined at the grid-point scale are explicitly quantified. The importance of ARs in inducing these events increases with latitude. Poleward of about 83° N, 100 % of these events occurred under AR conditions, corroborating that ARs were essential in contributing to the occurrence of these events. Over the past 4 decades, both the frequency, duration, and magnitude of these events have been increasing significantly. As the Arctic continues to warm, these events are likely to increase in both frequency, duration, and magnitude, with great implications for the local sea ice, hydrological cycle, and ecosystem. 

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