Effects of the tropospheric large-scale circulation on European winter temperatures during the period of amplified Arctic warming.

We investigate factors influencing European winter (DJFM) air temperatures for the period 1979-2015 with the focus on changes during the recent period of rapid Arctic warming (1998-2015). We employ meteorological reanalyses analysed with a combination of correlation analysis, two pattern clustering techniques, and back-trajectory airmass identification. In all five selected European regions, severe cold winter events lasting at least 4 days are significantly correlated with warm Arctic episodes. Relationships during opposite conditions of warm Europe/cold Arctic are also significant. Correlations have become consistently stronger since 1998. Large-scale pattern analysis reveals that cold spells are associated with the negative phase of the North Atlantic Oscillation (NAO-) and the positive phase of the Scandinavian (SCA+) pattern, which in turn are correlated with the divergence of dry-static energy transport. Warm European extremes are associated with opposite phases of these patterns and the convergence of latent heat transport. Airmass trajectory analysis is consistent with these findings, as airmasses associated with extreme cold events typically originate over continents, while warm events tend to occur with prevailing maritime airmasses. Despite Arctic-wide warming, significant cooling has occurred in northeastern Europe owing to a decrease in adiabatic subsidence heating in airmasses arriving from the southeast, along with increased occurrence of circulation patterns favouring low temperature advection. These dynamic effects dominated over the increased mean temperature of most circulation patterns. Lagged correlation analysis reveals that SCA- and NAO+ are typically preceded by cold Arctic anomalies during the previous 2-3 months, which may aid seasonal forecasting.

Decadal Bering Sea seascape change: consequences for Pacific walruses and indigenous hunters.

The most significant factors currently affecting the Pacific walrus (Odobenus rosmarus divergens) population are climate change and consequent changes in sea-ice morphology and dynamics. This paper integrates recent physical sea-ice change in the Bering Sea with biological and ecological conditions of walruses in their winter-spring reproductive habitat. Historically, walrus in winter-spring depended on a critical mass of sea-ice habitat to optimize social networking, reproductive fitness, feeding behavior, migration, and energetic efficiency. During 2003-2013, our cross-disciplinary, multiscale analysis from shipboard observations, satellite imagery, and ice-floe tracking, reinforced by information from indigenous subsistence hunters, documented change of sea-ice structure from a plastic continuum to a "mixing bowl" of ice floes moving more independently. This fragmentation of winter habitat preconditions the walrus population toward dispersal mortality and will also negatively affect the availability of resources for indigenous communities. We urge an expanded research and management agenda that integrates walrus natural history and habitat more completely with changing sea-ice morphology and dynamics at multiple scales, while also meeting the needs of local communities.

A major ecosystem shift in the northern Bering Sea.

Until recently, northern Bering Sea ecosystems were characterized by extensive seasonal sea ice cover, high water column and sediment carbon production, and tight pelagic-benthic coupling of organic production. Here, we show that these ecosystems are shifting away from these characteristics. Changes in biological communities are contemporaneous with shifts in regional atmospheric and hydrographic forcing. In the past decade, geographic displacement of marine mammal population distributions has coincided with a reduction of benthic prey populations, an increase in pelagic fish, a reduction in sea ice, and an increase in air and ocean temperatures. These changes now observed on the shallow shelf of the northern Bering Sea should be expected to affect a much broader portion of the Pacific-influenced sector of the Arctic Ocean.