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Permafrost soils store a substantial part of the global soil carbon and nitrogen. However global warming causes abrupt erosion and gradual thaw, which make these stocks vulnerable to microbial decomposition into greenhouse gases. Here, we investigated the microbial response to abruptin situpermafrost thaw. We sequenced the total RNA of a 1 m deep soil core consisting of up to 26’500-year-old permafrost material from an active abrupt erosion site. We analysed the microbial community in the active layer soil, the recently thawed, and the intact permafrost and found maximum RNA:DNA ratios indicating a microbial bloom in recently thawed permafrost. Several fast-growing prokaryotic taxa dominated thawed permafrost, including Sphingobacteriales, Burkholderiales, and Nitrosomonadales. Overall, the thaw state and soil moisture consistently explained changes in community composition, with especially the permafrost community being significantly distinct from thawed soils. Predation correlated with changes in prokaryotic composition. Bacterial grazers were dominated by Myxococcales and abundant in the active layer. In contrast, protozoa, especially Cercozoa and Ciliophora, doubled in relative abundance in thawed layers. Our findings highlight the ecological importance of a rapid development of microbial blooms as well as the successive predation as biological control mechanism in abruptly thawing permafrost.One sentence summaryUsing total RNA from an up to 26’500-year-old abruptly eroding permafrost site in Greenland, we described a microbial bloom and its controls, including bacterial and microeukaryotic predators.Abstract Figure

The Greenland Ecosystem Monitoring programme (GEM) is the most comprehensivelong-term ecosystem monitoring programme in the Arctic. Operationalsince 1995, GEM is now every year adding to more than 25 years of observationscovering ecosystems on land, ice, snow and in fresh and marine waters. GEM monitors seasonal fluctuations together with changes through the yearsand these time series are complemented by monitoring across a climate gradientstretching from high Arctic Zackenberg/Daneborg in North East Greenlandto Qeqertarsuaq, Disko Island on the boundary of the high and low Arcticand further south to low Arctic Nuuk.The long-term interdisciplinary data collection carried out by Greenlandic andDanish institutions makes GEM a key provider ofknowledge on status and changes in the arctic natural environments to ArcticCouncil working groups (AMAP andCAFF) and global assessmentorganizations like IPCC and IPBES. This is theAnnual report for the GEM programme in 2021.&nbsp

The continuous change in observed key indicators such as increasing nitrogen deposition, temperatures and precipitation will have marked but uncertain consequences for the ecosystem carbon (C) sink-source functioning of the Arctic. Here, we use multiple in-situ data streams measured by the Greenland Ecosystem Monitoring programme in tight connection with the Soil-Plant-Atmosphere model and climate projections from the high-resolution HIRHAM5 regional model. We apply this modelling framework with focus on two climatically different tundra sites in Greenland (Zackenberg and Kobbefjord) to assess how sensitive the net C uptake will expectedly be under warmer and wetter conditions across the 21st century and pin down the relative contribution to the overall C sink strength from climate versus plant trait variability. Our results suggest that temperatures (5–7.7 °C), total precipitation (19–110 %) and vapour pressure deficit will increase (32–36 %), while shortwave radiation will decline (6–9 %) at both sites by 2100 under the RCP8.5 scenario. Such a combined effect will, on average, intensify the net C uptake by 9–10 g C m−2 year−1 at both sites towards the end of 2100, but Zackenberg is expected to have more than twice the C sink strength capacity of Kobbefjord. Our sensitivity analysis not only reveals that plant traits are the most sensitive parameters controlling the net C exchange in both sites at the beginning and end of the century, but also that the projected increase in the net C uptake will likely be similarly influenced by future changes in climate and existing local nutrient conditions. A series of experiments forcing realistic changes in plant nitrogen status at both sites corroborates this hypothesis. This work proves the unique synergy between monitoring data and numerical models to assist robust model calibration/validation and narrow uncertainty ranges and ultimately produce more reliable C cycle projections in understudied regions such as Greenland.

The regional variability in tundra and boreal carbon dioxide (CO

The Arctic is changing in response to ongoing warming. Multiple effects have been documented in terms of sea-ice distribution, land-ice volume and ecosystems both in the marine and terrestrial realm, which are clear responses to the overall global warming. Targeted efforts documenting individual components of the arctic system build the base-line for quantification of these effects.Comprehensive ecosystem observational programs covering both glacial, terrestrial and marine components are rare in the Arctic but one such, the Greenland Ecosystem Monitoring (GEM) program, has now been operational for nearly 25 years at three main sites in Greenland. Zackenberg valley and Young Sund in NE Greenland is representing the high-arctic environment, Disko Island on the central west coast of Greenland at the border between the high and the low-arctic and Nuuk-Kobbefjord in SW Greenland the low-arctic.The GEM program at all three sites cover inter-annual variation in ecosystem dynamics of glacial, terrestrial and marine ecosystems with data gathered from more than 2000 parameters some of which being automatically recorded at very high frequencies (up to 20 Hz for micro-meteorological measurements). This present-day detailed, comprehensive and high-frequency monitoring of ecosystem dynamics calls for the question: Which historical sources may be used in order to anchor the environmental status of the monitored areas back in time?For the composite landscape dynamics including glacier, terrestrial and near-coastal environments it is of great value to study visual, mainly photographic evidences that are available from different parts of the portfolio of arctic exploration during the 19th and 20th centuries. We will in this presentation review available historical archival data (early photographs, paintings, drawings) from the GEM monitoring locations and their immediate surroundings.The different historical setting over the centennial timescale is briefly discussed and particular illustrative records from the individual sites are shown. The evidence of change hereby shown at the centennial time scale is evaluated in the perspective of results from decadal scale present day monitoring.