Vital Signs

Estimates of the spatial extent of melting across the Greenland ice sheet in 2015, derived from spaceborne brightness temperatures recorded by the Special Sensor Microwave Imager/Sounder (SSMIS) passive microwave radiometer (e.g., Mote 2007; Tedesco 2007; Tedesco et al. 2013), show that melting occurred over more than half of the ice sheet for the first time since the exceptional melt events of July 2012…

Sea ice extent is the primary descriptor of the state of the Arctic sea ice cover. Satellite-based passive microwave instruments have been used to determine sea ice extent since 1979…

Summer sea surface temperatures (SSTs) 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, respectively. Solar warming of the ocean surface layer is influenced by the distribution of sea ice (with more solar warming in ice-free regions), and by cloud cover, water color and upper-ocean stratification…

Primary productivity is the rate at which atmospheric or aqueous carbon dioxide is converted by autotrophs (primary producers) to organic material. It occurs most commonly by photosynthesis (i.e., with light as an energy source) but it is also facilitated by chemosynthesis (i.e., using oxidation of methane or other reduced inorganic molecules as an energy source instead of light).

Until recently, the above-ground biomass of Arctic tundra vegetation had been increasing, i.e., vegetation has been “greening”, for at least the past three decades (Bhatt et al. 2013, Frost and Epstein 2014)…