KR Miner1, CE Miller1, Rachel Mackelprang2, Arwyn Edwards3

1. Jet Propulsion Laboratory, California Institute of Technology
2. California State University at Northridge, California USA
3. Aberystwyth University, Wales, UK

Climate change accelerates permafrost degradation throughout the Arctic, introducing known and unknown biotoxicological hazards previously sequestered in permafrost.1

While infrastructure failures due to permafrost thaw are well documented, the biological, chemical and radiation hazards released as permafrost thaws are less understood. Both point source and disperse biotoxicological hazards present a diversity of potentially overlapping risks as the Arctic thaws. Only minimally characterized, the emergence of methanogenic bacteria, unclassified viruses, bacteria, and pathogens notably bring unknown paleo-ecosystem dynamics into the modern age.2 These species join various anthropogenic materials, including banned organic pesticides, mercury, oil, and nuclear remnants. However, variability within Arctic permafrost environments results in additional uncertainty in the location, timing, and rate of emergence for these hazards. The known locations of point-source dispersal include mining areas (Arsenic (As), Cd, Nickel (Ni)), Camp Century (~240km from Thule, Greenland), and nuclear test and submarine scuttle sites in the Russian Arctic (Kara and Barents Sea).1 Secondary, or non-point source emissions include the release of organochlorine pollutants from glaciers,3 atmospheric mercury deposition and environmental transport of microbes.

In order to understand the dynamics of this emergent risk from the new Arctic, there is an urgent need to quantify the risks before they emerge. To do this, a combination of remote sensing, in situ, and modeling are needed to better integrate micro-scale dynamics (including permafrost thaw) into Earth systems models. Paralleling the growing impacts of carbon transformation and release as methane, biotoxicological hazards are poised to become a new source of toxins in the environment as the New Arctic continues to change.


1. Miner, K. R. et al. Emergent biogeochemical risks from Arctic permafrost degradation. Nat. Clim. Chang. (2021) doi:https://doi.org/10.1038/s41558-021-01162-y.
2. Edwards, A. et al. Microbial genomics amidst the arctic crisis. Microb. Genomics 6, 1–20 (2020).
3. Miner, K. R. et al. A screening-level approach to quantifying risk from glacial release of organochlorine pollutants in the Alaskan Arctic. J. Expo. Sci. Environ. Epidemiol. 29, (2018).

Carbon dioxide (CO2) and methane (CH4) have been recognized by the International Panel of Climate Change (IPCC) as the most important of the Earth's greenhouse gases which are directly modified by human activities and which are the main contributors to global warming.
In order to reliably predict the climate of our planet, and to help inform political conventions on greenhouse gas emissions such as the Paris Agreement of 2015, adequate knowledge of both natural and anthropogenic sources of these greenhouse gases (GHG) and their feedbacks is needed. Despite the recognized importance of this issue, our current understanding about sources and sinks of CO2 and CH4 is still inadequate. This is particularly true for the Arctic, where large wetlands and permafrost areas constitute the most relevant but least quantified ecosystems for the global carbon budget.

The Arctic is warming twice as fast as the global average, making climate change’s polar effects more intense than anywhere else in the world. The Arctic accounts for half of the organic carbon stored in soils, and rising temperatures and thawing permafrost threaten its stability. The release of CO2 and CH4 from thawing permafrost will amplify global warming and further accelerate permafrost degradation. Fires in boreal forests and tundra peatlands are direct sources of CH4 and CO2 and also accelerate the thawing of permafrost, leading to the release of carbon. There is increasing, but divergent, evidence that a changing climate in the modern period has already shifted these ecosystems from net sinks of carbon to net sources, or will do so in the near future. The high-latitude natural sources also overlap with geologic CH4 sources (e.g. natural gas seeps in the Mackenzie delta), as well as anthropogenic sources from fossil fuel excavation in e.g. Alaska or Alberta, making the separation of natural vs. anthropogenic signals difficult.

Two methodologies are used to infer GHG emissions in order to understand the global carbon budget: The bottom-up approach assesses emissions by aggregating inventories fed by data about fuel consumption, local activity data, and vegetation models. In contrast, the top-down approach is based on atmospheric measurements and inverse modelling. While the latter offers the potential to verify reported emissions with independent measurements, the two approaches still disagree to a degree that prevents accurate budgeting of the major greenhouse gases and fails to fully explain recent atmospheric trends.

Three prerequisites are required to optimally apply the top-down methodology: First, the atmosphere must be measured at high spatial and temporal resolution via networks of ground-based stations and aircraft. Second, remote sensing is necessary, from satellites to give global coverage, from the ground to calibrate the satellite data, and from aircraft to bridge the scales. Third, modelling is needed, to synthesize the results and convert the concentration measurements to surface fluxes.

The CoMet 2.0 mission intends to address this objective with a multi-disciplinary approach providing relevant measurements from Arctic regions using a sophisticated suite of scientific instrumentation onboard the German research aircraft HALO to support state-of-the-art Earth system models. At the same time, CoMet intends to support and improve current and future satellite missions, which struggle to make high-quality measurements given the low sun elevation, low albedo, and adverse cloud conditions in the Arctic.
CoMet 2.0 Arctic is foreseen for a six-week intensive operation period from August to mid-September 2022 targeting boreal wetlands and permafrost areas in the Alaskan and Canadian Arctic and potentially embedded oil and gas extraction sites. A total of 120 flight hours, including transfer flights from Germany, are planned, enabling approximately 11-13 scientific flights on site.
CoMet 2.0 is a sequel to CoMet 1.0, which was successfully carried out in Europe in 2018 and concentrated on anthropogenic emissions and instrument tests. CoMet 2.0 shall now transfer the methodologies developed during the first mission to the Arctic region (and, at a later stage, into the tropics).

The High Altitude and LOng Range Research Aircraft (HALO) is a research platform for atmospheric and Earth system research, operated by the German Aerospace Center (DLR) on behalf of a consortium consisting of major German research centers and universities. Originally a standard Gulfstream G550 twin-engine jet aircraft, the aircraft has been significantly modified to make it suitable for scientific use. HALO has a maximum range of about 10 000 km or > 10-h endurance, a ceiling altitude of 14.5 km and is able to carry a scientific payload of up to 3000 kg.

For the CoMet 2.0 mission, HALO will be equipped with a suite of sophisticated instruments measuring the CO2 and CH4 columns between the aircraft and the ground using remote sensing, as well as in-situ instruments. The remote sensing package comprises the CH4 and CO2 lidar CHARM-F (Amediek et al., 2017) and the imaging spectrometer MAMAP2DL. Both instruments act as demonstrators for upcoming greenhouse gas missions. CHARM-F is operated by DLR and designed as the airborne demonstrator for the upcoming German-French MERLIN mission (Ehret et al. 2017). MAMAP2DL is operated by University of Bremen with significant similarities to the spectrometer foreseen for the Copernicus CO2 Monitoring Mission (CO2M) (Janssens-Maenhout et al., 2020). The remote sensors are supported by several in-situ instruments to measure the main greenhouse gases and related trace species as well an air sampler that collects air samples at flight level for later analysis in the laboratory. Furthermore, instruments to provide detailed information about the standard meteorological parameters (pressure, wind, humidity) will also be on board. In order to link those in-flight data to profiles, the launch of small meteorological sondes is foreseen.

CoMet 2.0 Arctic will be coordinated in conjunction with the Arctic-Boreal Vulnerability Experiment (ABoVE) which is a NASA Terrestrial Ecology Program field campaign conducted in Alaska and Western Canada (Miller et al., 2019). ABoVE is a large-scale study of environmental change and its implications for social-ecological systems focused on gaining a better understanding of the vulnerability and resilience of Arctic and boreal ecosystems to environmental change and providing the scientific basis for informed decision-making to guide societal responses from local to international levels. Both missions, ABoVE and CoMet 2.0, are linked through the transatlantic initiative AMPAC (Arctic Methane and Permafrost Challenge) that has recently been inaugurated by the US and European Space Agencies, NASA and ESA.

 
References:

Amediek, A., G. Ehret, A. Fix, M. Wirth, C. Büdenbender, M. Quatrevalet, C. Kiemle, and C. Gerbig, "CHARM-F—a new airborne integrated-path differential-absorption lidar for carbon dioxide and methane observations: measurement performance and quantification of strong point source emissions," Appl. Opt. 56, 5182-5197 https://doi.org/10.1364/AO.56.005182 (2017).

Ehret, G., P. Bousquet, C. Pierangelo, M. Alpers, B. Millet, J.B. Abshire, H. Bovensmann, J.P. Burrows, F. Chevallier, P. Ciais, C. Crevoisier, A. Fix, P. Flamant, C. Frankenberg, F. Gibert, B. Heim, M. Heimann, S. Houweling, H.W. Hubberten, P. Jöckel, L. Law, A. Löw, J. Marshall, A. Agusti-Panareda, S. Payan, C. Prigent, P. Rairoux, T. Sachs, M. Scholze, M. Wirth, “MERLIN: A French-German Space Lidar Mission Dedicated to Atmospheric Methane,” Remote Sens. 9, 1052 https://doi.org/10.3390/rs9101052 (2017).

Fix, A., A. Amediek, C. Büdenbender, G. Ehret, C. Kiemle, M. Quatrevalet, M. Wirth, S. Wolff, H. Bovensmann, A. Butz, M. Gałkowski, C. Gerbig, P. Jöckel, J. Marshall, J. Nęcki, K. Pfeilsticker, A. Roiger, J. Swolkień, M. Zöger and the CoMet team “CH4 and CO2 IPDA Lidar Measurements During the Comet 2018 Airborne Field Campaign,” EPJ Web Conferences 237, 03005 https://doi.org//10.1051/epjconf/202023703005 (2020).

Janssens-Maenhout, G., Pinty, B., Dowell, M., Zunker, H., Andersson, E., Balsamo, G., Bézy, J.-L., Brunhes, T., Bösch, H., Bojkov, B., Brunner, D., Buchwitz, M., Crisp, D., Ciais, P., Counet, P., Dee, D., Denier van der Gon, H., Dolman, H., Drinkwater, M. R., Dubovik, O., Engelen, R., Fehr, T., Fernandez, V., Heimann, M., Holmlund, K., Houweling, S., Husband, R., Juvyns, O., Kentarchos, A., Landgraf, J., Lang, R., Löscher, A., Marshall, J., Meijer, Y., Nakajima, M., Palmer, P. I., Peylin, P., Rayner, P., Scholze, M., Sierk, B., Tamminen, J., & Veefkind, P. (2020). Toward an Operational Anthropogenic CO2 Emissions Monitoring and Verification Support Capacity, Bulletin of the American Meteorological Society, 101(8), E1439-E1451. https://doi.org/10.1175/BAMS-D-19-0017.1 (2020).

Miller, C. E., Griffith, P., Goetz, S., Hoy, E., Pinto, N., McCubbin, I., Thorpe, A. K., Hofton, M. M., Hodkinson, D. J., Hansen, C., Woods, J., Larsen, E. K., Kasischke, E. S., and Margolis, H. A.: An overview of ABoVE airborne campaign data acquisitions and science opportunities, Environ. Res. Lett. 14(8), 080201, https://doi.org/10.1088/1748-9326/ab0d44 (2019).

The inability to accurately quantify methane (CH4) emissions across spatial scales has led to large uncertainties in the Arctic CH4 budget and its future contributions to the permafrost carbon feedback. Our analysis of AVIRIS data from the Arctic Boreal Vulnerability Experiment (ABoVE) Airborne Campaigns revealed microtopographic CH4 hotspots in diverse ecosystems across the ABoVE domain [Elder 2020]. We quantified relationships of these CH4 hotspots with extraordinary fluxes and sub-surface permafrost thaw at local scales [Elder 2021] and with geomorphological controls at regional scales [Baskaran 2021; Elder 2021]. In parallel, we developed a novel L-band SAR algorithm to measure bubbles trapped in winter ice to quantify CH4 ebullition in lakes [Engram 2020], giving us unprecedented insights into terrestrial and aquatic CH4 hotspots. The scaling analyses that we have pioneered in the ABoVE domain anticipate the extension of these methods to the pan-Arctic with the launch of the NASA-ISRO SAR mission (NISAR, LRD 2023), NASA’s Surface Biology and Geology mission (SBG, LRD 2028) as well as ESA’s Copernicus expansion missions CHIME (LRD 2028) and ROSE-L (LRD 2028). Similarly, comparisons of our AVIRIS and SAR products with the CHARM-F and MAMAP2D CH4 products to be acquired during the 2022 ABoVE-CoMet 2.0 Arctic campaign in Alaska and NW Canada [Fix 2018] will accelerate science return from the MERLIN (LRD 2027) and CO2-M (LRD 2026) missions. These analyses will provide critical insights into the CH4 component of the permafrost carbon feedback and enable the use of satellites to monitor its trajectory on interannual to decadal time scales.

References
Baskaran, L, CD Elder, DR Thompson, AA Bloom, S Ma, CE Miller, Geomorphological Patterns of Remotely Sensed Methane Hot Spots in the Mackenzie Delta, Canada, Environmental Research Letters (ABoVE Special Collection), Manuscript No.: ERL-112521, accepted

Elder, C. D., Thompson, D. R., Thorpe, A. K., Hanke, P., Walter Anthony, K. M., & Miller, C. E. (2020). Airborne mapping reveals emergent power law of Arctic methane emissions. Geophysical Research Letters, 47, e2019GL085707. https://doi.org/10.1029/2019GL085707

Elder, Clayton D., David R. Thompson, Andrew K. Thorpe, Latha Baskaran, Philip J. Hanke, Stephanie James, Burke Minsley, Neal Pastick, Katey M. Walter Anthony, Charles E. Miller, 2021. Characterizing Extreme Methane Emissions from Thermokarst Hotspots, Global Biogeochemical Cycles, Advance Online: 2 December 2021. https://doi.org/10.1029/2020GB006922

Engram, M., Anthony, K.W., Sachs, T., Kohnert, K., Serafimovich, A., Grosse, G. and Meyer, F.J., 2020. Remote sensing northern lake methane ebullition. Nature Climate Change, 10(6), pp.511-517. https://doi.org/10.1038/s41558-020-0762-8

Fix, A., Amediek, A., Bovensmann, H., Ehret, G., Gerbig, C., Gerilowski, K., Pfeilsticker, K., Roiger, A. and Zöger, M., 2018. CoMet: An airborne mission to simultaneously measure CO2 and CH4 using lidar, passive remote sensing, and in-situ techniques. In EPJ Web of Conferences (Vol. 176, p. 02003). EDP Sciences. https://doi.org/10.1051/epjconf/201817602003

Atmospheric methane concentration has been constantly increasing over the past decades with a record-high growth rate in 2020 since the systematic measurements began in 1984. The measurements suggest a significant increase in atmospheric methane from the high latitudes in 2020 but what role Arctic methane emissions were playing is still unclear. One of the major challenges for resolving this question is the limited understanding of methane fluxes from natural wetlands during the non-growing season, which constitute up to 40% of annual Arctic methane emissions based on ground-based measurements. However, current process-based models largely underestimate the methane fluxes during the non-growing season. This leads to bias in the seasonality of Arctic methane fluxes and thus affects the estimates of Arctic methane budgets given their biased priori distributions in atmospheric inversions. Satellite retrievals are ideal to provide continuous measurements in the spatio-temporal domain. However, current satellite retrievals of column methane concentration by passive instruments, i.e., GOSAT and TROPOMI, are limited by solar zenith angle at high latitudes and unable to make retrievals during the non-growing season. Here we propose an airborne-based remote sensing technique, the High-Altitude Lidar Observatory (HALO) based on the differential absorption lidar (DIAL) and high spectral resolution lidar (HSRL) techniques to measure weighted atmospheric methane column concentrations, aerosol and cloud distributions, and planetary boundary layer heights for the Arctic during the non-growing season. We conduct a preliminary analysis with a dynamic global vegetation model (LPJ-wsl) and an atmospheric inversion model to demonstrate how non-growing season fluxes are missing in the current Arctic methane budget. By comparing with TROPOMI column methane observations, we show how active remote sensing of column methane is needed to enhance our understanding and monitoring of the Arctic methane budget. The new measurement could provide accuracy and sensitivity needed for improving the understanding of Arctic methane budget and serves as an airborne simulator for the Atmospheric Boundary Layer Lidar Pathfinder (ABLE), a cross-cutting active trace gas lidar mission concept aimed at measuring methane and water vapor from affordable space-based platforms.

Vast areas of the Arctic host ice-rich permafrost and with climate warming these permafrost regions become increasingly vulnerable to thaw. This thaw manifest itself first in a slow but gradual deepening of the seasonally thawed active layer (press disturbances) and secondly in a more rapid and local way by the development of thermokarst features (pulse disturbances).Both forms of permafrost degradation have major impacts by changing ecosystem and hydrological equilibria, and impact the Earth system on a global scale by reinforcing climate change with the additional mobilization of organic carbon that was previously stored in the frozen soil. One important thermokarst feature arising from pulse disturbances are retrogressive thaw slumps (RTS). RTSs initiate by the exposure of ice-rich soils with a subsequent thaw and the formation of a steep headwall. During the summer, the ice in the headwall melts which leads to a continuous retreat. This process can mobilize vast quantities of sediments on a time-scale of years. In the context of recent climate warming, an increase in the number and sizes of RTSs in permafrost regions has been found. However, the inter-regional differences in the rates of RTS activity in terms of their magnitude, distribution and controls remain poorly constrained and so are the implications for carbon and nutrient cycles.
For the investigation of landslides in temperate climate zones, frequency distributions and scaling laws of various form have been used to quantify hazards and ecosystem impacts as well as to improve the process understanding of landslide activity. The variability and similarities of these laws in terms of landslides properties and area characteristics have played an important role. The soil properties (ice-content) as well as time-scales (single event vs. polycyclic multi-year retreat) are different for RTSs than for other landslides, but nevertheless the methods used as well as the universality of landslide characteristics could provide valuable insights into RTS drivers and controls. Furthermore, due to the strong spatial variability of soil organic carbon densities as well as RTS activity past model estimates of the impacts of RTSs on the carbon cycle have large uncertainties. Quantifying the induced volumetric change rates and associated RTS frequency distributions and scaling laws as well as the variability across regions have the potential to greatly improve future carbon release rates.

In this presentation we will show results of an analysis where we used digital elevation models generated from TanDEM-X observations to derive volume and area change rates for RTSs across the Arctic. In a first part we compare RTS characteristics based on elevation model differences over a 5-year time-period from winter 2011/12 to winter 2016/17 and contrast 10 study sites (Eurasia: 5, North America: 5), with a total size of 220.000 km^3 and a total of 1853 RTSs in the sample. We found inter-regional differences in mobilized volumes, scaling laws and terrain controls. The distributions of RTS area and volumetric change rates follow a probability density function known from landslides in temperate climate zones with a distinct peak and an exponential decrease for the largest RTSs. We found that the distributions in the high Arctic are shifted towards larger values, than at other study sites. We also analyzed the area-to-volume scaling, which can potentially be used to estimate volumetric changes when only area change measurements are available.
In a second part we will show first results of a study on the northern Taymyr Peninsula, Siberia, where additional to the time-period from winter 2011/12 to winter 2016/17 observations in 2017/18 and 2020/21 are available. This allows us to investigate temporal changes in the RTS activity and scaling laws. Here we found a strong increase in all quantities describing RTS activity. For example the number of RTSs increased from 82 to 1404 RTSs. With the additional usage of higher temporal resolution Sentinel-2 images we could attribute the strong increase to the 2020 Siberian heatwave. Furthermore, with the use of soil organic carbon maps and several model assumptions estimating unknowns like the ground-ice content, we quantified for the first time the amount of soil organic carbon over a large region that is mobilized due to RTS activity.
Our results have the potential to improve the modelling and monitoring of Arctic carbon, nutrient and sediment cycles and can guide future satllite missions and observation stategies.

The climate change is affecting in a dramatic way the Arctic, which is warming faster than any other place in the Earth. How will the melting permafrost change the surface properties and how will the changes affect the potential methane emissions in the Arctic? This is the key question of the ESA-NASA joint initiative AMPAC - Arctic Methane and Permafrost Challenge, launched in 2019. To answer this challenging goal collaboration and coordinated joint efforts between different research communities are crucially needed.

At present, there are large discrepancies in the emission estimates based on bottom-up and top-down techniques. The AMPAC Working group WG.1 focuses on improving the various observations that can contribute to reducing the differences. In this presentation, we discuss the status of the satellite-based methane observations at high latitudes and permafrost regions and recent advances in the algorithms. With this presentation we aim to contribute to the WG.1 by supporting interaction between different observation communities in comparing the observations, evaluating the spatial and seasonal variability of observations, improving the interpretation of the data and in identifying observational gaps.