Abstracts – Session C2
Thawing permafrost carbon: a challenge for climate science
C201 ORAL-0045: Long-term carbon budget and ecosystem response to climate variability for a high arctic tundra ecosystem
Wenxin Zhang1, Per-Erik Jansson1, Guy Schurgers1, Bo Elberling1
1University of Copenhagen, Copenhagen, Denmark
High arctic tundra ecosystems respond to recent climatic warming by stimulating C fluxes which represent both potential C sources and sinks. However, there is still a large uncertainty in reconciling the estimate of ecosystem C budget not the least in arctic ecosystems with continuous permafrost, which may cause specific impacts due to thawing. Here, we customized a process-oriented model (CoupModel) to quantify different components of C budget at a Cassiope tetragona heath ecosystem in Northeast Greenland. The model was successfully constrained to reproduce observed C, heat and water fluxes over 15 years based on a Monte-Carlo multi-run calibration. We conclude that annual net ecosystem exchange (NEE) for 2000-2014 was -15 ± 10.3 g C m-2 yr-1. The significant trends for most above- and below-ground C fluxes and stocks were found for two sub-periods (i.e. 2000-2008 and 2008-2014) but not for the entire period. The cumulative non-growing season C fluxes were found to have a minor contribution to the annual C budget but with a tendency of increase as spring burst of the observed C fluxes. Inter-annual variabilities of photosynthesis (GPP), ecosystem respiration (ER) and NEE were found significantly correlated with July temperature and annual maximum thawing depth, the latter of which also determines decomposition rate of the old C. Overall, our study highlights that a sink-source transition of the studied ecosystem depends on ecosystem responses to seasonal change of climate, and the net C balance is subject to summer warmth and annual maximum thawing depth.
C202 - ORAL-0199: Controls of soil organic matter on permafrost thermal and carbon dynamics
Dan Zhu1, Philippe Ciais1, Gerhard Krinner2, Fabienne Maignan3, Albert Jornet-Puig3
1Laboratoire des Sciences du Climat et de l’Environnement, LSCE CEA CNRS UVSQ, Gif Sur Yvette, France 2CNRS, Univ. Grenoble Alpes, Institut de Géosciences de l’Environnement (IGE), grenoble, France 3Laboratoire des Sciences du Climat et de l'Environnement (LSCE), Gif-sur-Yvette, France
Soils in the northern permafrost regions contain large quantities of organic carbon, formed under cold climates with limited decomposition; meanwhile, soil organic carbon (SOC) significantly modifies soil thermal and hydraulic properties, and in turn affects soil thermo- and hydro-dynamics, vegetation growth, and soil carbon accumulation. Typically, the presence of SOC cools soil temperature during summer due to its lower soil thermal conductivity and higher heat capacity. SOC also alters hydraulic properties towards higher plant-available water capacity. Both processes may enhance soil organic carbon accumulation and therefore form a positive feedback loop.
In this study, we analyzed the influential factors of soil thermal diffusivities inferred from more than 200 sites in Siberia with depth-specific measurements of monthly soil temperature, and found SOC to be the most important factor among all the tested factors including SOC, soil texture-related properties, bulk density and soil moisture. We then incorporated the effects of SOC on soil thermal and hydrological processes in the ORCHIDEE-MICT land surface model. We showed that the inclusion of SOC effects significantly decreases modeled summer soil temperature and active layer thickness in permafrost regions, which is in better agreement with site observations. Consequently, modeled present-day soil organic carbon in northern permafrost region increase by 27%, from 800 PgC to 1016 PgC. Such SOC-thermics coupling may be important for future permafrost dynamics under climate change, since the loss of permafrost carbon can accelerate soil warming due to a smaller insulating.
C203 - ORAL-0295: Examining Environmental Gradients in permafrost regions – the ESA GlobPermafrost project
Annett Bartsch1, Guido Grosse2, Andreas Kääb3, Sebastian Westermann4, Tazio Strozzi5, Antonie Haas2, Birgit Heim2, Ingmar Nitze2, Sebastian Laboor2, Jaroslav Obu4, Frank Martin Seifert6
1ZAMG, Vienna, Austria 2AWI, Potsdam, Germany 3University of Oslo, Oslo, Norway 4University Oslo, Oslo, Norway 5Gamma Remote Sensing, Gümligen, Switzerland 6ESA, Frascati, Italy
Permafrost cannot be directly detected from space, but many surface features of permafrost terrains and typical periglacial landforms are observable with a variety of EO sensors ranging from very high to medium resolution at various wavelengths. In addition, landscape dynamics associated with permafrost changes and geophysical variables relevant for characterizing the state of permafrost, such as land surface temperature or freeze-thaw state can be observed with space-based Earth Observation. Suitable regions to examine environmental gradients across the Arctic have been defined in a community white paper (Bartsch et al. 2014). These transects have been revised and adjusted within the ESA DUE GlobPermafrost project.
The ESA DUE GlobPermafrost project develops, validates and implements Earth Observation (EO) products to support research communities and international organisations in their work on better understanding permafrost characteristics and dynamics. Prototype product cases will cover different aspects of permafrost by integrating in situ measurements of subsurface properties and surface properties, Earth Observation, and modelling to provide a better understanding of permafrost today. The project will extend local process and permafrost monitoring to broader spatial domains, support permafrost distribution modelling, and help to implement permafrost landscape and feature mapping in a GIS framework. It will also complement active layer and thermal observing networks. Both lowland (latitudinal) and mountain (altitudinal) permafrost issues are addressed.
The status of the Permafrost Information System and first results will be presented. This includes prototypes of GlobPermafrost datasets, and the permafrost information system through which they can be accessed.
Special emphasis will be on the use of satellite data for land surface characterization with respect to soil properties such as soil organic carbon.
C204 - ORAL-0134: Extra climate mitigation required to offset permafrost thawing
Eleanor Burke1, Sarah Chadburn2, Chris Huntingford3
1Met Office, Exeter, United Kingdom 2leeds University, Leeds, United Kingdom 3Centre for Ecology & Hydrology, Wallingford, United Kingdom
Large amounts of carbon are locked up in the permafrost of the northern high latitudes. As this permafrost degrades under climate change some of this carbon will decompose and may be released to the atmosphere. Any positive permafrost carbon feedback will reduce the natural carbon sinks and hence the anthropogenic emissions in order to achieve the goals of the Paris Agreement. Model simulations using the JULES-IMOGEN intermediate complexity climate model and a stabilization target of 2 deg C, show that at 2100 the mean land sink (without the permafrost carbon pool) is between 0.3 and 1.6 Gt C / year. This is projected to reduce to between 0.1 and 1.4 Gt C / year when including the permafrost carbon pool. Inertia in the permafrost carbon system means that permafrost carbon loss may continue for many years after the anthropogenic emissions have stabilized. For example, by 2500 the simulated land sink (without the permafrost carbon pool) is projected to weaken to between 0.05 and 0.4 Gt C / year. Including the permafrost carbon pool which emits 0.08 to 0.16 Gt C / year will change the land from a sink to a source of carbon in some model realisations. These results suggest that the permafrost carbon pool should be taken into account when developing carbon budgets and designing mitigation activities to achieve long term low carbon stabilization targets. Uncertainties caused by the parameterisation of the permafrost carbon decomposition processes are much larger than uncertainties in either the climate response or stabilization temperature target.
C205 - POSTER-0270: The Influence of Shrub Expansion on Permafrost Thawing in Arctic
Zhan Wang1, Yeonjoo Kim1
1Yonsei University, Seoul, The Republic Of Korea
The vegetation in Arctic has increased for decades with land cover and vegetation type change. In order to isolate the influence of the shrub expansion on the permafrost thawing, the Arctic terrestrial ecosystem in recent decades will be simulated using the Community Land Model (CLM) with and without the vegetation dynamics. The simulated snowpack, surface energy exchange, soil heat flux and the active layer thickness will be compared between the CLM-Carbon Nitrogen Model (CN) and the CLM-Carbon Nitrogen Dynamic Global Vegetation Model (CNDV). Furthermore the Moderate Resolution Imaging Spectroradiometer (MODIS) land cover product (MCD12Q1) will be utilized to evaluate the outcomes of vegetation dynamics in CLM-CNDV.
C206 - POSTER-0347: Snow-Vegetation-Topography-Permafrost Interactions in the Seward Peninsula, Alaska
Cathy Wilson1, Robert Bolton2, Robert Busey2, Lauren Charsley-Groffman1, Stan Wullschleger3
1Los Alamos National Laboratory, Los Alamos, The United States of America 2University of Alaska, Fairbanks, Fairbanks, The United States of America 3Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, The United States of America
Snow is a critical factor in determining hydrologic, thermal, and ecological processes in Arctic landscapes. Snow depth and density, as well as the timing and duration of snow cover directly influence the thermal regime of frozen ground; runoff and wetland replenishment; snow-vegetation-atmosphere energy exchanges; and the timing and duration of biogeochemical processes driving CO2 and CH4 emissions. A key goal of the US DOE NGEE-Arctic project is to understand and predict how spatial heterogeneity in snow interacts with vegetation, topography and permafrost in response to changing climate. NGEE-Arctic researchers are acquiring snow precipitation, depth, density, ground temperature, snow water equivalent, vegetation structure and permafrost depth data at hilly sites in the Seward Peninsula, AK. These data are collected at a range of spatial and temporal scales using meteorological stations, in-situ gridded and transect-based surveys, ground-based geophysics, and Unmanned Aerial System mapping techniques. NGEE-Arctic modelers are developing statistical and deterministic models to represent the interactions between snow and landscape characteristics to develop a predictive understanding of the coupled evolution of snow, vegetation and permafrost. Data from our preliminary 2016 snow, permafrost and vegetation surveys at the NGEE-Arctic Teller Road site are demonstrating positive correlations between tall vegetation, deeper snow and deeper permafrost. We are applying the ATS model with our data to quantify these relationships for different vegetation height, density and patch size configurations in order to better parameterize arctic land-atmosphere system processes in DOE's ACME global climate model. To improve the statistical robustness of our 2017 surveys we use representative analysis to classify the landscape into key ecotype-topotype units to inform and guide our sampling strategy. This approach should allow us to scale our understanding and prediction of snow–landscape interactions, and their evolution with changing climate, from the hillslope to the watershed and larger regions throughout the Pan-Arctic domain.