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Organic carbon in the top layer of mineral soils in cold regions is dominated by the particulate fraction, according to analyses in Arctic and alpine ecosystems.

Longer periods of biogeochemical connectivity in soil porewaters with a deeper active layer suggest early organic carbon transport during the dormant season, according to silicon isotope compositions of permafrost soil porewaters in Alaska.

Considering cryosphere and warming uncertainties together implies drastically increased risk of threshold crossing in the cryosphere, even under lower-emission pathways, and underscores the need to halve emissions by 2030 in line with the 1.5 °C limit of the Paris Agreement.

An international team of researchers finds high potential for improving climate projections by a more comprehensive treatment of largely ignored Arctic vegetation types, underscoring the importance of Arctic energy exchange measuring stations.

It is unclear whether climate driven phenological shifts of tundra plants are consistent across the plant growing season. Here the authors analyse data from a network of field warming experiments in Arctic and alpine tundra, finding that warming differentially affects the timing and duration of reproductive and vegetative phenology.

Mechanisms and consequences of the acclimation of soil respiration to warming are unclear. Here, the authors combine soil respiration, metagenomics, and functional gene results from a 7-year grassland warming experiment to a microbial-enzyme decomposition model, showing functional gene information to lower uncertainty and improve fit.

Analyses of inventory models under two climate change projection scenarios suggest that carbon emissions from abrupt thaw of permafrost through ground collapse, erosion and landslides could contribute significantly to the overall permafrost carbon balance.

Winter warming in the Arctic will increase the CO₂ flux from soils. A pan-Arctic analysis shows a current loss of 1,662 TgC per year over the winter, exceeding estimated carbon uptake in the growing season; projections suggest a 17% increase under RCP 4.5 and a 41% increase under RCP 8.5 by 2100.

Soil radiocarbon dating reveals that combusted ‘legacy carbon’—soil carbon that escaped burning during previous fires—could shift the carbon balance of boreal ecosystems, resulting in a positive climate feedback.

Permafrost loses carbon at a faster rate than previously thought as climate warms, according to direct soil carbon observations over five years in the field in Alaska’s tundra ecosystem.

The sudden collapse of thawing soils in the Arctic might double the warming from greenhouse gases released from tundra, warn Merritt R. Turetsky and colleagues.

The magnitudes of replenishment and priming, two important but opposing fluxes in soil organic carbon (SOC) dynamics, have not been compared. Here the authors show that the magnitude of replenishment is greater than that of priming, resulting in a net SOC accumulation after additional carbon input to soils.

A meta-analysis of soil incubation studies from the permafrost zone suggests that thawing under aerobic conditions, which releases CO₂, will strengthen the permafrost carbon feedback more than waterlogged systems, which releases CO₂ and CH₄.

Release of carbon previously locked in permafrost is a potentially important positive climate feedback. Now metagenomics reveal the vulnerability of active-layer soil carbon to warming-induced microbial decomposition in Alaskan tundra.

Research utilizing C isotopes to partition ecosystem respiration sources in a subarctic warming experiment shows that old soil contributions increased with soil temperature but that carbon losses were modulated by plant responses to warming.

The long-term loss of carbon from thawing permafrost in Northeast Greenland is quantified for 1996–2008 by repeated sediment sampling and incubation. Although the active layer has increased by >1 cm per year, there has not been a detectable decline in carbon stocks. Laboratory studies highlight the potential for fast carbon mobilization under aerobic conditions, but indicate that carbon at near-saturated conditions may remain largely immobilized for decades.

Northern soils will release huge amounts of carbon in a warmer world, say Edward A. G. Schuur, Benjamin Abbott and the Permafrost Carbon Network.

Ecosystems acquire nitrogen from the atmosphere, but this source can't account for the large nitrogen capital of some systems. The finding that bedrock can also act as a nitrogen source may help solve the riddle. See Letter p.78

Permafrost thaw and microbial decomposition is considered one of the most likely positive climate feedbacks from terrestrial ecosystems to the atmosphere in a warmer world, but the rate of carbon release from permafrost soil remains highly uncertain. Here, net ecosystem carbon exchange is measured in a tundra landscape undergoing permafrost thaw to determine the influence of old carbon loss on ecosystem carbon balance. The results reveal significant losses of soil carbon over decadal time scales, overwhelming the increased carbon uptake from plants.