Abstract. High-latitude soils store vast amounts of perennially frozen and therefore inert organic matter. With rising global temperatures and consequent permafrost degradation, a part of this carbon stock will become available for microbial decay and eventual release to the atmosphere. We have developed a simplified, two-dimensional multi-pool model to estimate the strength and timing of future carbon dioxide (CO2) and methane (CH4) fluxes from newly thawed permafrost carbon (i.e. carbon thawed when temperatures rise above pre-industrial levels). We have especially simulated carbon release from deep deposits in Yedoma regions by describing abrupt thaw under newly formed thermokarst lakes. The computational efficiency of our model allowed us to run large, multi-centennial ensembles under various scenarios of future warming to express uncertainty inherent to simulations of the permafrost carbon feedback. Under moderate warming of the representative concentration pathway (RCP) 2.6 scenario, cumulated CO2 fluxes from newly thawed permafrost carbon amount to 20 to 58 petagrams of carbon (Pg-C) (68% range) by the year 2100 and reach 40 to 98 Pg-C in 2300. The much larger permafrost degradation under strong warming (RCP8.5) results in cumulated CO2 release of 42 to 141 Pg-C and 157 to 313 Pg-C (68% ranges) in the years 2100 and 2300, respectively. Our estimates only consider fluxes from newly thawed permafrost, not from soils already part of the seasonally thawed active layer under pre-industrial climate. Our simulated CH4 fluxes contribute a few percent to total permafrost carbon release yet they can cause up to 40% of total permafrost-affected radiative forcing in the 21st century (upper 68% range). We infer largest CH4 emission rates of about 50 Tg-CH4 per year around the middle of the 21st century when simulated thermokarst lake extent is at its maximum and when abrupt thaw under thermokarst lakes is taken into account. CH4 release from newly thawed carbon in wetland-affected deposits is only discernible in the 22nd and 23rd century because of the absence of abrupt thaw processes. We further show that release from organic matter stored in deep deposits of Yedoma regions crucially affects our simulated circumpolar CH4 fluxes. The additional warming through the release from newly thawed permafrost carbon proved only slightly dependent on the pathway of anthropogenic emission and amounts to about 0.03–0.14 °C (68% ranges) by end of the century. The warming increased further in the 22nd and 23rd century and was most pronounced under the RCP6.0 scenario, adding 0.16 to 0.39 °C (68% range) to simulated global mean surface air temperatures in the year 2300.

[1] We investigate the surface morphology of a study area in western Utopia Planitia, Mars, which is characterized by a variety of landforms that resemble those of terrestrial periglacial landscapes. Polygonally fractured ground and thermokarst-like depressions are found to be located in a young mantling deposit with a thickness of several tens of meters. We observe a latitudinal dependence of the degradation of this mantling deposit. Larger depressions, whose floors reveal the underlying basement rocks, cover a higher fraction of the total terrain in the southern part of the study area than in the northern part, indicating a more intense degradation of the mantle in the south. All depressions have an asymmetric cross section in north-south direction, interpreted to be the result of the different solar radiation on differently oriented slopes. On the basis of our morphological observations, we develop a conceptual model for landscape evolution in western Utopia Planitia. It involves subaerial deposition of a layered, ice-rich mantle and its subsequent degradation by polygon formation and sublimation. A terrestrial analog to the polygonally fractured mantling deposit and its thermokarst-like depressions is the Siberian Ice Complex or ''Yedoma,'' which consists of subaerial ice-rich deposits and is connected to nonglaciated landscapes with highly continental cold-climatic environmental conditions. Our comparison suggests that no unusual or exotic processes need to be invoked to explain the current morphology of western Utopia. However, the young age of the deposition and degradation implies climatic excursions in the very recent past on Mars.

Abstract. Distinctive periglacial landscapes have formed in late-Pleistocene ice-rich permafrost deposits (Ice Complex) of northern Yakutia, Siberia. Thermokarst lakes and thermokarst basins alternate with ice-rich Yedoma uplands. We investigate different thermokarst stages in Ice Complex deposits of the Lena River Delta using remote sensing and geoinformation techniques. The morphometry and spatial distribution of thermokarst lakes on Yedoma uplands, thermokarst lakes in basins, and thermokarst basins are analyzed, and possible dependence upon relief position and cryolithological context is considered. Of these thermokarst stages, developing thermokarst lakes on Yedoma uplands alter ice-rich permafrost the most, but occupy only 2.2 % of the study area compared to 20.0 % occupied by thermokarst basins. The future potential for developing large areas of thermokarst on Yedoma uplands is limited due to shrinking distances to degradational features and delta channels that foster lake drainage. Further thermokarst development in existing basins is restricted to underlying deposits that have already undergone thaw, compaction, and old carbon mobilization, and to deposits formed after initial lake drainage. Future thermokarst lake expansion is similarly limited in most of Siberia's Yedoma regions covering about 10 6 km 2 , which has to be considered for water, energy, and carbon balances under warming climate scenarios.

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