ALBERT

Description: Permafrost a common formation in the Arctic and Sub-arctic region: As a result of the strong negative temperature balance in the Polar region, almost 25 % of the land areas of the earth are underlain by permafrost. Permafrost dominates the landscape and ecosystems of the large tundra and boreal forest areas of Northern Eurasia and North America, where it can reach thicknesses of more than 1000 m. Formed in Siberia since the Late Pliocene, permafrost has the largest extension in lowland regions non-glaciated during the Pleistocene, where permafrost never disappeared completely during last warm phases. Due to the low global sea level in glacial periods, terrestrial permafrost has been formed on the large Arctic shelf, where now submerged subsea permafrost still exists as relict of up to 400 m depth below the sea bottom. The glacial-interglacial climate dynamics during the Quaternary are mirrored in permafrost and landscape dynamics in the Arctic and Subarctic. The relief of these regions is mainly controlled by periglacial and nival processes, where periglacial landforms are strongly connected to the formation or degradation of permafrost. Especially ice-rich permafrost is very sensitive to climate warming, which results in degradation processes, such as thermokarst, thermoerosion and coastal retreat. The observed warming of the Arctic results in an increasing of the active layer thickness, a rise in permafrost temperature, and in the disappearance of discontinuous permafrost at the southern boundary. The concurrent increase in the amounts of precipitation and melt water will further intensify thermokarst processes and thaw consolidation and will result in the formation of bogs and swamps. Permafrost degradation will result in complex changes of the geoecosystems, an increase of greenhouse gas emission due to enhanced organic matter decomposition, and a destabilization of permafrost regions, which are used by men for living and for economic use. Furthermore, anthropogenic activities lead to an additional destabilization of the thermal equilibrium of frozen ground affecting the stability of constructions and buildings.

Description: Arctic permafrost coasts are eroding at rates similar or greater than temperate coasts and release large quantities of organic carbon and nitrogen previously stored in permafrost. Estimates of organic carbon fluxes from ice-rich permafrost coasts of the Laptev Sea, where data is scarce, differ widely with estimates varying by two orders or magnitude. Here, we used high resolution datasets on coastal erosion, cryostratigraphy, organic carbon and geomorphology from the Bykovsky Peninsula, in the southern Laptev Sea, to compute below ground organic carbon and nitrogen pools and fluxes of organic carbon from the coast for the current period and the next hundred years. Frozen deposits of the peninsula contain 141.6 Tg of organic carbon, a number 27% lower than what it would contain if the surface had not been affected by permafrost thaw in the past. An additional 44.0 Tg of organic carbon is contained under the peninsula below current sea level. The current fluxes of organic carbon from the peninsula are estimated at 0.058 Tg C a-1 and future fluxes at 0.067 Tg C a-1, or even at 0.085 Tg C a-1 if below sea level organic carbon stocks are included in the calculation. Extrapolation of these measurements to the entire Yedoma coast of the Laptev Sea gives an maximum annual flux of organic carbon from coastal erosion of 6.95 Tg C a-1, which ranges between the previously published minimum and maximum estimations for the same area.s

Description: The transition from onshore to offshore permafrost during periods of low relative sea level rise is often the result of coastal retreat. Along the Laptev Sea coastline, ice-rich syngenetic permafrost is particularly susceptible to erosion due to changing climate, and coastal retreat floods about 10 km2 of permafrost each year. Changes to permafrost immediately after flooding provide an opportunity to study the mechanism of submarine permafrost degradation in general. Recent studies have drawn a link between observed methane release on the Laptev Sea shelf and surmised permafrost degradation. We combine direct observations of permafrost and methane to investigate the possibility of methane release from permafrost as a source. Our studies focus on a site in Buor Khaya Bay in the central Laptev Sea, for which coastal retreat rates have been studied. Following geophysical reconnaissance, we drilled a 52 m deep core in the near-shore zone of the eastern shore of Buor Khaya Bay and measured the permafrost temperature in the resulting borehole. Comparison of the submarine permafrost temperature to temperatures on land reveal warming of permafrost by 8 to 10 °C over a period of less than a millennium. During this time, the top of the ice-bearing permafrost (IBPF) degraded from 0 to 28.8 m b.s.l. at the borehole site, a mean degradation rate of almost 3 cm per year. Geoelectric resistivity measurements corroborate this observation and show a decline of the IBPF with increasing distance from shore. Similar to many other Siberian locations, the deeper permafrost at the study site contained less organic carbon by orders of magnitude when compared to the overlying syngenetic ice complex deposits. The same held true for methane concentrations in the frozen permafrost. Our data suggest that these comparatively low concentrations of methane are oxidized in the sediment column upon thawing. Analyses of the sediment and pore water chemistry demonstrate that sea water is probably advected to the IBPF, which contributes to permafrost degradation and provides sulfate for methane oxidation at the top of the thawing permafrost.

Description: The Lena River Delta in Northern Yakutia forms one of the largest deltas in the Arctic and its catchment area (2 430 000 km2) is one of the largest in the whole of Eurasia. The study site is one of the coldest and driest places on Earth, with a mean annual air temperatures of about -13 °C, a large annual air temperature range of about 44 °C and summer precipitation usually less than 150 mm. Permafrost plays a major role for storage and release of water to rivers and surface and subsurface water bodies. Very cold continuous permafrost of about −8.6°C underlays the area between about 400 and 600 m below the surface and since 2006 the permafrost has warmed more than 1°C at 10.7 m. Roughly half of the land surface is dominated by wet surfaces, such as polygons, thermokarst lakes and ponds. Ponds are generally well mixed and experience high water temperatures up to 23°C during the summer and therefore are hotspots for biological activity and CO2 emission. Compared to the gaseous emissions, however, the lateral export of dissolved carbon from the polygonal tundra was negligible due to the small volumes of runoff. The ponds in the study area freeze completely in winter, whereas the deeper thermokarst lakes do not freeze to the bottom. These deep thermokarst lakes are thermally stratified during winter and reach maximum water temperatures of up to 19°C during summer. There are distinct differences in the zooplankton community between ponds and lakes, depending on their hydrological and chemical characteristics. Most productive ecosystems are thermokarst ponds with a high abundance of zooplankton and biomass. The summer water balance at the catchment scale was found to be mainly controlled by vertical fluxes (precipitation and evapotranspiration). Overall, the long-term summer storage (precipitation minus evapotranspiration) in the polygonal tundra from 1958-2011 is reasonably balanced with an average surplus of 5 mm. But it is also characterized by high inter-annual variability due to changes in precipitation. During negative water balance years where evapotranspiration exceeds precipitation, shallow water bodies dry out. This indicates that the extent of wetlands and water bodies will shift with changes in vertical water fluxes as well as permafrost warming and thaw.

Description: Arctic permafrost coasts make up about one third of the global coastline and are likely to witness some of the most dramatic changes linked to changing environmental conditions in the 21st century. Increasing sea level, warming sea temperatures, longer open water season and increasing open-water area all bear the potential to increase the impact on sediment and nutrient pathways in the nearshore zone. In this study, we focus on a well studied location, the Bykovsky Peninsula, southern Laptev Sea, Russia to provide high resolution estimations of organic carbon release from its coastline. We build on recently published datasets from studies related to coastal geomorphology, paleogeography and oceanography, all available at large scale, to map and determine the fluxes of carbon coming from the coast throughout the second half of the twentieth century and to provide prospective numbers on the release of organic carbon in the years to come.

Description: The northern permafrost region contains approximately 50% of the estimated global below-ground organic carbon pool and more than twice as much as is contained in the current atmos-pheric carbon pool. The sheer size of this carbon pool, together with the large amplitude of predicted arctic climate change im-plies that there is a high potential for global-scale feedbacks from arctic climate change if these carbon reservoirs are desta-bilized. Nonetheless, significant gaps exist in our current state of knowledge that prevent us from producing accurate assess-ments of the vulnerability of the arctic permafrost to climate change, or of the implications of future climate change for global greenhouse gas (GHG) emissions. Specifically: • Our understanding of the physical and biogeochemical processes at play in permafrost areas is still insuffi-cient in some key aspects • Size estimates for the high latitude continental carbon and nitrogen stocks vary widely between regions and research groups. • The representation of permafrost-related processes in global climate models still tends to be rudimentary, and is one reason for the frequently poor perform-ances of climate models at high latitudes. The key objectives of PAGE21 are: • to improve our understanding of the processes affect-ing the size of the arctic permafrost carbon and nitro-gen pools through detailed field studies and monitor-ing, in order to quantify their size and their vulnerability to climate change, • to produce, assemble and assess high-quality datasets in order to develop and evaluate representations of permafrost and related processes in global models, • to improve these models accordingly, • to use these models to reduce the uncertainties in feed-backs from arctic permafrost to global change, thereby providing the means to assess the feasibility of stabili-zation scenarios, and • to ensure widespread dissemination of our results in order to provide direct input into the ongoing debate on climate-change mitigation. The concept of PAGE21 is to directly address these questions through a close interaction between monitor- ing activities, proc-ess studies and modeling on the pertinent temporal and spatial scales. Field sites have been selected to cover a wide range of environmental conditions for the validation of large scale mod-els, the devel- opment of permafrost monitoring capabilities, the study of permafrost processes, and for overlap with existing monitoring programs. PAGE21 will contribute to upgrading the project sites with the objective of providing a measurement baseline, both for process studies and for modeling programs. PAGE21 is determined to break down the traditional barriers in permafrost sciences between observational and model-supported site studies and large-scale climate modeling. Our concept for the interaction between site-scale studies and large-scale modeling is to establish and maintain a direct link be-tween these two areas for developing and evaluating, on all spatial scales, the land-surface modules of leading European global climate models taking part in the Coupled Model Inter-comparison Project Phase 5 (CMIP5), designed to inform the IPCC process. The timing of this project is such that the main scientific results from PAGE21, and in particular the model-based assessments will build entirely on new outputs and results from the CMIP5 Climate Model Intercomparison Project designed to inform the IPCC Fifth Assessment Report. However, PAGE21 is designed to leave a legacy that will en-dure beyond the lifetime of the projections that it produces. This legacy will comprise • an improved understanding of the key processes and parameters that determine the vulnerability of arctic permafrost to climate change, • the production of a suite of major European coupled climate models including detailed and validated repre- sentations of permafrost-related processes, that will reduce uncertainties in future climate projections pro-duced well beyond the lifetime of PAGE21, and • the training of a new generation of permafrost scien-tists who will bridge the long-standing gap between permafrost field science and global climate modeling, for the long-term benefit of science and society.

Description: Coastal erosion and relative sea-level rise inundate terrestrial permafrost with seawater and create submarine permafrost. Once flooded, permafrost begins to warm under marine conditions, which can destabilize the sea floor. The timing of inundation can be inferred from the rate of coastline retreat and the distance from the shoreline. Coastline retreat rates are inversely related to the inclination of the upper surface of submarine ice-bonded permafrost. Submarine permafrost thaw is considered to be a cause for recent observations of methane emissions from the seabed to the water column and atmosphere of the East Siberian shelf. A 52 m long core drilled from the sea ice in Buor Khaya Bay, central Laptev Sea revealed unfrozen sediment overlying ice-bonded permafrost. Dissolved methane and sulfate concentrations are inversely related along the core with higher methane and lower sulfate contents in the ice-bonded submarine permafrost relative to the overlying unfrozen sediment. The observed profiles of sediment pore water sulfate concentrations, as well as methane concentrations and methane stable carbon isotope ratios, indicate that methane from ice-bonded permafrost is oxidized at or immediately following thaw. Anaerobic oxidation of methane in the unfrozen sediment column between ice-bonded permafrost and the seabed makes it unlikely that methane from thawing submarine permafrost could reach the seabed.

Description: Our understanding of the physical and biogeochem- ical processes at play in permafrost areas has been greatly inadequate and significant gaps have existed in our current knowledge, hindering any accurate as- sessment of the vulnerability of Arctic permafrost to climate change, or of the implications of future climate change for global greenhouse gas (GHG) emis- sions. The PAGE21 project was designed to broaden our knowledge base by assessing the vulnerability of Arctic permafrost to climate change and by reducing the uncertainties in permafrost-related feedbacks to the global climate. In particular, the PAGE21 project has sought to answer the following questions: • What are the key processes and parameters in- fluencing and controlling the vulnerability of the carbon and nitrogen pools in Arctic permafrost to future climate change? • How large an effect will Arctic climate change feedback (due to changes in the carbon and ni- trogen pools contained in permafrost) have on anthropogenic global warming? The concept of PAGE21 was to address these ques- tions through a close interaction between monitoring activities, process studies and modeling on the per- tinent temporal and spatial scales. Field sites were selected to cover a wide range of environmental condi- tions for the validation of large scale models, the de- velopment of permafrost monitoring capabilities, the study of permafrost processes, and for overlap with existing monitoring programs. Interaction between site-scale studies and large-scale modeling was de- signed to establish and maintain a direct link between these two areas for developing and evaluating, on all spatial scales, the land-surface modules of lead- ing European global climate models taking part in the Coupled Model Intercomparison Project Phase 5 (CMIP5), designed to inform the IPCC process. The PAGE21 results to date have highlighted that the amount of carbon released from permafrost over the 21st century may not be as large as previously claimed. The project has found an average loss of about 50 Gt C by 2100, which is at the lower end of the IPCC estimate of 50 to 250 Gt C. However, we have found that, in a much warmer world, this carbon loss would continue over hundreds of years leading to the severe degradation of permafrost ecosystems and a large cumulative loss of previously frozen carbon

Description: The MEthane Remote sensing Lidar missioN (MERLIN) aims at demonstrating the spaceborne active measurement of atmospheric methane, a potent greenhouse gas, based on an Integrated Path Differential Absorption (IPDA) nadir-viewing LIght Detecting and Ranging (Lidar) instrument. MERLIN is a joint French and German space mission, with a launch currently scheduled for the timeframe 2021/22. The German Space Agency (DLR) is responsible for the payload, while the platform (MYRIADE Evolutions product line) is developed by the French Space Agency (CNES). The main scientific objective of MERLIN is the delivery of weighted atmospheric columns of methane dry-air mole fractions for all latitudes throughout the year with systematic errors small enough (〈3.7 ppb) to significantly improve our knowledge of methane sources from global to regional scales, with emphasis on poorly accessible regions in the tropics and at high latitudes. This paper presents the MERLIN objectives, describes the methodology and the main characteristics of the payload and of the platform, and proposes a first assessment of the error budget and its translation into expected uncertainty reduction of methane surface emissions.