ALBERT

Description: Until now permafrost carbon feedback modeling has focused on gradual thaw of near-surface permafrost in terrestrial environments, which leads to enhanced carbon dioxide (CO2) and methane (CH4) emissions that accelerate global climate warming. The state-of-the-art land models do not simulate emissions from deeper permafrost thaw beneath thermokarst lakes or other abrupt-thaw processes, and so have not quantified the impact of abrupt thaw on the permafrost carbon feedback. We reanalyzed output from the Community Land Model (CLM4.5BGC), to quantify carbon emissions originating from gradual permafrost thaw in the terrestrial environment, and added to this box-model-projected permafrost carbon emissions from abrupt thaw beneath thermokarst lakes. Simulations spanned 2010 to 2100 under moderate and high Representative Concentration Pathways (RCP4.5 and RCP8.5). Supported by field observations, radiocarbon dating, and remote sensing, this re-analysis of model data leads to four striking conclusions. First, accounting for abrupt permafrost thaw beneath lakes more than doubles the radiative effect of circumpolar permafrost carbon release in the 21st century beyond that of gradual thaw alone. Second, permafrost carbon emissions from lakes are similar under RCP4.5 and RCP8.5, but their contribution to the circumpolar permafrost carbon radiative effect (CPCRE) is much larger under the moderate warming scenario. Third, CH4, not CO2, is the dominant driver of the CPCRE, responsible for up to ~70% of circumpolar permafrost-carbon radiative forcing this century. Finally, including abrupt thaw beneath lakes, a process that accelerates mobilization of ancient, deeply frozen carbon, increases old permafrost soil carbon (C-CO2e) emissions by ~125% to 190% compared to gradual thaw alone. Since abrupt thaw has not been considered in earth system models, these findings have important implications for climate change scientists and policy makers, who will now need to account for a 〉100% larger radiative effect from permafrost carbon loss this century.

Description: Permafrost affects about 24% of the Northern Hemisphere land surface. Organic carbon storage in soils and deep deposits in these regions exceeds 1000 Pg and has resulted in a long-term carbon sink to the atmosphere. A large portion of this carbon is perennially frozen and radiocarbon dates ranging from Holocene to Late Pleistocene ages indicate it has been removed from active cycling for thousands of years. In a warming Arctic, understanding how short-term processes and their feedbacks with climate might interfere with long-term permafrost soil carbon storage is of crucial importance to projecting future trajectories of climate. For example, complex landscape and biogeochemical dynamics in northern wetlands and lake-rich regions may lead to decomposition of soil organic carbon under anaerobic conditions and significant methane release to the atmosphere. Here we focus on the role of lakes in permafrost regions for the mobilization of old organic carbon from permafrost deposits in the form of methane. Lake cover is especially extensive (up to 40% limnicity) in northern permafrost lowlands associated with thick ice- and organic-rich deposits. A large portion of these lakes are thermokarst lakes that rapidly thaw underlying and surrounding permafrost soils, providing organic-rich anaerobic environments for methane production in thaw bulbs and lake sediments. However, various other types of lakes exist and multiple drivers affect how and at what rates various lake types may interact with permafrost and soil organic carbon. We discuss new broad-scale remote sensing, spatial data analysis, and modeling approaches that allow an assessment of the methane emission potentials of northern high latitude lakes in relation to permafrost and surface deposits.

Description: In this NASA ABoVE-funded project, we combine geospatial data products derived from airborne and spaceborne remote sensing (RS) data with targeted field observations and modeling in order to quantify ecosystem responses to Arctic and boreal environmental change. Specifically, we quantify methane (CH4) ebullition (bubbling) emissions associated with 60 years of permafrost thaw in thousands of Alaskan and NW Canadian lakes by direct observation with RS systems. To achieve our goals, we have developed statistically-significant models that are using SAR, optical and infrared RS data in order to detect and quantify CH4 ebullition emissions at intra-, whole- and regional-lake scales. We also established a relationship between observed CH4 ebullition and average annual soil organic carbon (SOC) inputs to a handful of Alaskan lakes via thermokarst-margin expansion during recent decades using field data, radiocarbon dating and modeling. Our paper we will provide an overview of the goals, datasets, and methods used for the various components of this project. We will present on (1) the collection of new and synthesis of existing field data on CH4 ebullition, thaw-bulbs and SOC; (2) the analysis of existing data from aerial surveys, SAR and optical RS of CH4 in lake ice; (3) the orthorectification of historic aerial photos for comparison to high-resolution satellite imagery to produce fine-scale regional maps of lake area change, (4) the modelling of permafrost SOC quantities eroded into lakes; (5) the radiocarbon dating of CH4 and SOC, (6) GIS modeling to produce multi-temporal regional maps of historic lake area change, associated CH4 emissions, and permafrost SOC stocks; and (7) outreach to stakeholders at Alaska village and rural community field sites. To demonstrate the scientific relevance of our work we will also showcase a set of research results that we have been able to achieve so far. These will include (1) first regional-scale RS-based estimates of lake-borne CH4 ebullition emissions; (2) regional scale estimates of lake area change from an analysis of 50 years of remote sensing data; and (3) regression models linking lake area change to CH4 emissions.