Links between winter sea-ice retreat, mid-latitudes atmospheric circulation, and long range transport of black carbon in the Arctic

The ongoing shrinkage of the Arctic sea ice cover is likely linked to the global temperature rise, the amplified warming in the Arctic, and possibly weather anomalies in the mid-latitudes. By applying a novel statistical method in climate science, the Independent Component Analysis (ICA), to global atmospheric energy anomalies in winters from 1980 to 2015, we show the link between the sea ice melting in the Arctic and the combination of only three atmospheric oscillation patterns approximating observed spatial variations of near-surface temperature trends in winter. Two of these large scale atmospheric circulation patterns connect by independent dynamical processes the sea ice melting and related atmospheric perturbations in the mid-latitudes. At the same time, we investigated the possible feedbacks of these independent dynamical processes on the long range transport of pollutants from the mid-latitudes to the Arctic. We focused in particular on the transport and deposition on Arctic sea-ice of black carbon (BC) aerosol particles, which may further impact the regional and global climate, through direct radiative forcing and by modifying the snow and sea-ice albedo. Winter anomalies of meteorological fields from the global reanalysis are processed together with BC surface concentrations and deposition simulated by a general circulation model coupled with atmospheric chemistry and physics (ECHAM5-HAMMOZ). The feedback of winter sea-ice retreat and surface temperature warming on the transport of BC to the Arctic was quantified with Maximum Likelihood Estimates of atmospheric concentrations and deposition of BC in the Arctic associated to the three independent atmospheric patterns. We found that negative anomalies of the NAO likely favor the transport of BC in the upper troposphere, with small deposition over the Arctic sea-ice. Stable high pressure systems (atmospheric blocking) near Scandinavia favour the near surface transport directly from Western Europe towards the Barents Sea, with increasing deposition over the sea-ice.