Report Card 2016

The Arctic sea ice cover is vast in areal extent covering millions of square kilometers, but is only a thin veneer a few meters thick. This ice cover plays many roles. It is a barrier limiting the exchange of heat, moisture, and momentum between the atmosphere and ocean; a home to a rich marine ecosystem, including human communities; and an indicator of climate change. Sea ice extent has been monitored using passive microwave instruments on satellite platforms since 1979. The months of September and March are of particular interest because they are the months when the Arctic sea ice typically reaches its maximum and minimum extent respectively.

Summer sea surface temperatures in the Arctic Ocean are set by absorption of solar radiation into the surface layer. In the Barents and Chukchi seas, there is an additional contribution from advection of warm water from the North Atlantic and Pacific Oceans (for a recent assessment of this in the Chukchi Sea, see Serreze et al., 2016). Solar warming of the ocean surface layer is influenced by the distribution of sea ice (with more solar warming in ice-free regions), cloud cover, water color, and upper-ocean stratification (river influxes influence the latter two).

Primary productivity is the rate at which atmospheric or aqueous carbon dioxide is converted by autotrophs (primary producers) to organic material. Primary production via photosynthesis is a key process within the ecosystem, as the producers form the base of the entire food web, both on land and in the oceans. The oceans play a significant role in global carbon budgets via photosynthesis. Approximately half of all global net annual photosynthesis occurs in the oceans, with ~10-15% of production occurring on the continental shelves alone (Müller-Karger et al. 2005). Primary productivity is strongly dependent upon light availability and the presence of nutrients, and thus is highly seasonal in the Arctic region. In particular, the melting and retreat of sea ice during spring are strong drivers of primary production in the Arctic Ocean and its adjacent shelf seas due to enhanced light availability…

Vegetation in the Arctic tundra has been responding dynamically over the course of the last several decades to environmental changes, many of which are anthropogenically-induced. These vegetation changes throughout the circumpolar Arctic are not spatially homogeneous, nor are they temporally consistent (e.g. Bhatt et al. 2013), suggesting that there are complex interactions among atmosphere, ground (soils and permafrost), vegetation, and herbivore components of the Arctic system. Changes in Arctic tundra vegetation may have a relatively small impact on the global carbon budget through photosynthetic uptake of CO₂, compared to changes in other carbon cycling processes (Abbott et al. 2016). However, tundra vegetation can have important effects on permafrost, hydrological dynamics, soil carbon fluxes, and the surface energy balance (e.g. Blok et el. 2010, Myers-Smith and Hik 2013, Parker et al. 2015). Tundra vegetation dynamics also control the diversity of herbivores (birds and mammals) in the Arctic, with species richness being positively related to vegetation productivity (Barrio et al. 2016). To improve our understanding of these complex interactions and their impacts on the Arctic and global systems, we continue to evaluate the state of the circumpolar Arctic vegetation.