Monitoring and Analysis of Frozen Debris Lobes, Phase I

INE/AUTC 12.2

Impact of Groundwater Flow on Permafrost Degradation and Transportation Infrastructure Stability

INE/AUTC 13.0

Present-day permafrost carbon feedback from thermokarst lakes

Rapid temperature rise during recent decades (IPCC 2013) is causing permafrost in the Arctic to warm and thaw. This thaw exposes previously frozen soil organic carbon (SOC) to microbial decomposition, generating greenhouse gases methane (CH4) and carbon dioxide (CO2) in a feedback process that leads to further warming and thaw. A growing number of studies model the future permafrost carbon feedback (PCF) to climate warming [Koven et al., 2015, Schneider von Deimling et al., 2015]. However, despite observations of widespread permafrost thaw during recent decades and forecasts of thaw during the next 25-100 years [Koven et al., 2015], no research has quantified the PCF for recent decades. This is in part due to the difficulty of detecting the net movement of old carbon from permafrost to the atmosphere over years and decades amidst large input and output fluxes from ecosystem carbon exchange. In contrast to terrestrial environments, thermokarst lakes provide a direct conduit for processing and emission of old permafrost carbon to the atmosphere, and these emissions are more readily detectable. Results here are based on Walter Anthony et al. [submitted], whereby we quantified the permafrost SOC input to a variety of thermokarst and glacial lakes in Alaska and Siberia in thermokarst zones, defined as areas where land surfaces have transitioned to open lakes due to permafrost thaw during the past 60 years, the historical period most commonly covered by remote-sensing data sets. We also quantified the resulting methane emitted from these active thermokarst lake zones. Using field work, numerical modeling of thaw bulbs, remote sensing and spatial data analysis we will report on the relationship between methane emissions from thermokarst zones and SOC inputs to lakes across gradients of permafrost and climate in Alaska. We will also define the relationship between radiocarbon ages of methane and permafrost soil carbon entering into lakes upon thaw. We will report on the presentday PCF relationship between thaw of permafrost SOC and resulting greenhouse gas release. An extrapolation of our results to the panarctic permafrost region will be presented and compared to permafrost carbon mass balance approaches. The fraction of the terrestrial permafrost carbon pool that has been released as methane from thermokarst along lake margins during the past 60 years will be evaluated relative to early Holocene thermokarst lake emissions and projected permafrost carbon emissions by year 2100. The data will be placed in the context of large regional temperature increases in the Arctic, up to 7.5 °C by 2100, and thicker, organic-rich Holocene-aged deposits subject to thaw and aerobic decomposition as active layer deepens. We will report on the inflection of large permafrost carbon emissions that is imminently expected to occur and whether or not it has commenced. References: Koven, C.D.; Schuur, E.A.G.; Schädel, C.; Bohn, T.J.; Burke, E.J.; Chen, G.; Chen, X.; Ciais, P.; Grosse, G.; Harden, J.W.; Hayes, D.J.; Hugelius, G.; Jafarov, E.E.; Krinner, G.; Kuhry, P.; Lawrence, D.M.; MacDougall, A.H.; Marchenko, S.S.; McGuire, A.D.; Natali, S.M.; Nicolsky, D.J.; Olefeldt, D.; Peng, S.; Romanovsky, V.E.; Schaefer, K.M.; Strauss, J.; Treat, C.C. and Turetsky, M. [2015]: A simplified, data-constrained approach to estimate the permafrost carbon–climate feedback. Trans. R. Soc. A, 373, doi:10.1098/rsta.2014.0423. Schneider von Deimling, T.; Grosse, G.; Strauss, J.; Schirrmeister, L.; Morgenstern, A.; Schaphoff, S.; Meinshausen, M. and Boike, J. [2015]: Observationbased modelling of permafrost carbon fluxes with accounting for deep carbon deposits and thermokarst activity. Biogeosciences, 12(11):3469–3488, doi:10.5194/bg-12-3469-2015. Walter Anthony, K.; Daanen, R.; Anthony, P.; Schneider von Deimling, T.; Ping, C.-L.; Chanton, J. and Grosse, G. [submitted]: Ancient methane emissions from ˜60 years of permafrost thaw in arctic lakes

Recent circum-Arctic ice-wedge degradation and its hydrological impacts

Ice-wedges are common permafrost features formed over hundreds to thousands of years of repeated frost cracking and ice vein growth. We used field and remote sensing observations to assess changes in areas dominated by ice-wedges, and we simulated the effects of those changes on watershed-scale hydrology. We show that top melting of ice-wedges and subsequent ground subsidence has occurred at multiple sites in the North American and Russian Arctic. At most sites, melting ice-wedges have initially resulted in increased wetness contrast across the landscape, evident as increased surface water in the ice-wedge polygon troughs and somewhat drier polygon centers. Most areas are becoming more heterogeneous with wetter troughs, more small ponds (themokarst pits forming initially at ice-wedge intersections and then spreading along the troughs) and drier polygon centers. Some areas with initial good drainage, such as near creeks, lake margins, and in hilly terrain, high-centered polygons form an overall landscape drying due to a drying of both polygon centers and troughs. Unlike the multi-decadal warming observed in permafrost temperatures, the ice-wedge melting that we observed appeared as a sub-decadal response, even at locations with low mean annual permafrost temperatures (down to −14 °C). Gradual long-term air and permafrost warming combined with anomalously warm summers or deep snow winters preceded the onset of the ice-wedge melting. To assess hydrological impacts of ice-wedge melting, we simulated tundra water balance before and after melting. Our coupled hydrological and thermal model experiments applied over hypothetical polygon surfaces suggest that (1) ice-wedge melting that produces a connected trough-network reduces inundation and increases runoff, and that (2) changing patterns of snow distribution due to differential ground subsidence has a major control on ice-wedge polygon tundra water balance despite an identical snow water equivalent at the landscape-scale. These decimeter-scale geomorphic changes are expected to continue in permafrost regions dominated by ice-wedge polygons, with implications for land-atmosphere and land-ocean fluxes of water, carbon, and energy

Methane emissions proportional to permafrost carbon thawed in Arctic lakes since the 1950s

Permafrost thaw exposes previously frozen soil organic matter to microbial decomposition. This process generates methane and carbon dioxide, and thereby fuels a positive feedback process that leads to further warming and thaw1. Despite widespread permafrost degradation during the past ~40 years2, 3, 4, the degree to which permafrost thaw may be contributing to a feedback between warming and thaw in recent decades is not well understood. Radiocarbon evidence of modern emissions of ancient permafrost carbon is also sparse5. Here we combine radiocarbon dating of lake bubble trace-gas methane (113 measurements) and soil organic carbon (289 measurements) for lakes in Alaska, Canada, Sweden and Siberia with numerical modelling of thaw and remote sensing of thermokarst shore expansion. Methane emissions from thermokarst areas of lakes that have expanded over the past 60 years were directly proportional to the mass of soil carbon inputs to the lakes from the erosion of thawing permafrost. Radiocarbon dating indicates that methane age from lakes is nearly identical to the age of permafrost soil carbon thawing around them. Based on this evidence of landscape-scale permafrost carbon feedback, we estimate that 0.2 to 2.5 Pg permafrost carbon was released as methane and carbon dioxide in thermokarst expansion zones of pan-Arctic lakes during the past 60 years

Pan-Arctic ice-wedge degradation in warming permafrost and its influence on tundra hydrology

Ice wedges are common features of the subsurface in permafrost regions. They develop by repeated frost cracking and ice vein growth over hundreds to thousands of years. Ice-wedge formation causes the archetypal polygonal patterns seen in tundra across the Arctic landscape. Here we use field and remote sensing observations to document polygon succession due to ice-wedge degradation and trough development in ten Arctic localities over sub-decadal timescales. Initial thaw drains polygon centres and forms disconnected troughs that hold isolated ponds. Continued ice-wedge melting leads to increased trough connectivity and an overall draining of the landscape. We find that melting at the tops of ice wedges over recent decades and subsequent decimetre-scale ground subsidence is a widespread Arctic phenomenon. Although permafrost temperatures have been increasing gradually, we find that ice-wedge degradation is occurring on sub-decadal timescales. Our hydrological model simulations show that advanced ice-wedge degradation can significantly alter the water balance of lowland tundra by reducing inundation and increasing runoff, in particular due to changes in snow distribution as troughs form. We predict that ice-wedge degradation and the hydrological changes associated with the resulting differential ground subsidence will expand and amplify in rapidly warming permafrost regions