Differing roles of North Atlantic oceanic and atmospheric transports in the winter Eurasian Arctic sea-ice interannual-to- decadal variability

The decline trend and interannual-to-decadal variability of sea-ice was found to be crucial for surface air temperature warming over the Arctic in winter. This study shows the physical cause of the interannual-to-decadal variability of the Eurasian Arctic sea-ice and their relative contributions.
Published in Earth & Environment
Differing roles of North Atlantic oceanic and atmospheric transports in the winter Eurasian Arctic sea-ice interannual-to- decadal variability
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In recent decades, the winter sea-ice concentration (SIC) over the Arctic especially over the Barents-Kara Sea (BKS) has undergone an accelerated decline since the 1990s, which may be the combined consequence of the long-term declining trend and interannual-to-decadal variability of the Arctic SIC. Rapid Arctic SIC decline in winter was found to be crucial for Arctic amplification represented by a rapid surface air temperature (SAT) rise over the Arctic region, which influences weather extremes and climate in midlatitude continents. While the increasing carbon dioxide (CO2) dominates the long-term declining trend of the Arctic SIC, the oceanic and atmospheric processes also modulate the interannual-to-decadal variability of the Arctic SIC. However, it is not clear what are the optimal modes of the interannual and decadal variability of the Eurasian Arctic SIC, respectively. Thus, further exploring the physical cause of the interannual-decadal variability of the Eurasian Arctic SIC and estimating their relative contributions are needed, which can help us improve the understanding of the predictability of the Arctic SIC variability.

By performing the empirical orthogonal function (EOF) analysis of winter mean SIC anomaly in the Eurasian Arctic region during 1950-2021, we obtained two modes of the SIC variability, which are the interannual monopole mode with an in-phase variation between the BKS and EG and the decadal dipole mode with an antiphase variation between the BKS and EG (second row in Figure 1). For the interannual SIC monopole mode (first column in Figure 1), using regression and composite analysis it is revealed that the decline of the Eurasian Arctic SIC with a monopole structure mainly results from the enhanced meridional atmospheric heat and moisture transports, and ocean heat transport (OHT) across Barents Sea opening (BSO) associated with positive Arctic dipole (AD) mode consisting of positive North Atlantic Oscillation (NAO) and Ural blocking (UB) on interannual timescales. Meanwhile, the North Atlantic SST anomaly with a cold-warm-cold tripole structure can favor enhanced interannual OHT from the North Atlantic to BKS through BSO. As for the SIC decadal dipole mode (second column in Figure 1), the Eurasian Arctic SIC with a zonal dipole between the BKS and EG is mainly produced by the opposite decadal variation of the OHT and atmospheric transport between the BKS and East Greenland (EG), which is related to the phase of Atlantic Multidecadal Oscillation (AMO) and Arctic Oscillation (AO) via modulating the decadal variability of oceanic and atmospheric processes. When the AMO is in positive phase, the BSO OHT along the Norwegian warm Atlantic Current (NwAC) and the cold current from high latitude Arctic region to the EG are both enhanced, which lead to an increase in the EG SIC and a decrease in the BKS SIC. Moreover, the negative AO consisting of a negative NAO and UB also favors this Eurasian Arctic SIC dipole mode via the opposite variation of meridional atmospheric transports between EG and BKS.

Finally, we use the multiple linear regression model to approximately evaluate the relative contributions of the atmospheric transport and OHT to the Eurasian Arctic SIC on interannual and decadal timescales, respectively. It is found that during 1960-2017 the relative contributions of the interannual atmospheric transport and OHT to the interannual variability of the Eurasian Arctic SIC are 66% and 34%, respectively. It is further revealed that the relative contributions of the decadal atmospheric transport and OHT to the decadal variability of the Eurasian Arctic SIC are 19% and 81%, which become 48% and 52% during 2000–2017, thus indicating that the contribution of the decadal atmospheric transport is intensified during 2000–2017 compared to during 1960–1999.

Figure 1. Schematic diagram illustrating the mechanism of interannual-to-decadal variability of the Eurasian Arctic SIC and estimating the different contributions of atmospheric heat and moisture transports and ocean heat transport to the variability of Eurasian Arctic SIC on interannual-decadal timescales. The second row shows the SIC interannual and decadal variations, respectively. The first and third rows show the atmospheric circulation and ocean heat transport associated with the SIC variability. The first (second) column represents the mechanism of Eurasian Arctic SIC variations on interannual (decadal) timescales. The percentages are the relative contributions of atmospheric and oceanic processes to the variability of the Eurasian Arctic SIC during 1960-2017.

Figure 1. Schematic diagram illustrating the mechanism of interannual-to-decadal variability of the Eurasian Arctic SIC and estimating the different contributions of atmospheric heat and moisture transports and ocean heat transport to the variability of Eurasian Arctic SIC on interannual-decadal timescales. The second row shows the SIC interannual and decadal variations, respectively. The first and third rows show the atmospheric circulation and ocean heat transport associated with the SIC variability. The first (second) column represents the mechanism of Eurasian Arctic SIC variations on interannual (decadal) timescales. The percentages are the relative contributions of atmospheric and oceanic processes to the variability of the Eurasian Arctic SIC during 1960-2017.

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Atmospheric Science
Physical Sciences > Earth and Environmental Sciences > Earth Sciences > Atmospheric Science
Ocean Sciences
Physical Sciences > Earth and Environmental Sciences > Earth Sciences > Ocean Sciences

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