ALBERT

Description: The land-ocean interface in the Arctic is a sensitive environment facing severe changes due to rising global air temperatures. In particular, Arctic river deltas are rapidly changing permafrost landscapes which will become more dynamic due to sea-level rise, longer thaw periods, changes in river discharge, increased storm-surge flooding and thawing permafrost. As a result, previously frozen river delta deposits are becoming available for microbial decomposition as permafrost thaws. However, very few studies have focused on Arctic deltas and estimates of deltaic carbon stocks are even more limited. Therefore, we compiled 140 soil cores (new and already published soil cores), consisting of more than 1400 samples from 17 different deltas around the Arctic Ocean. In addition, we mapped the spatial extent of more than 250 Arctic deltas in order to accurately assess the carbon and nitrogen stock estimations for Arctic deltas. Our study shows that Arctic river delta deposits contain a considerable amount of carbon and nitrogen. The ongoing thaw and degradation of these permafrost deposits resulting from global climate warming might release additional carbon and nitrogen with implications for Arctic waters and biogeochemical cycles. The additional export of terrestrial carbon and nitrogen will alter biogeochemical processes not only in the nearshore zone, but throughout the Arctic Ocean. With this study we will improve our understanding of changing terrestrial carbon and nitrogen deposits and their contribution to a changing Arctic Ocean.

Description: Arctic river deltas are sensitive polar landscapes at the land-ocean interface. In contrast to lower latitude deltas, Arctic deltas are characterized by low temperatures, a strong seasonality and the presence of permafrost. Seasonal freezing conditions and underlying permafrost hinders runoff for most of the year and leads to typical land forms such as ice wedge polygons, frost mounds and thermokarst lakes. However, compared to other permafrost dominated landscapes, Arctic deltas are more dynamic. The surface morphology is changing constantly due to river ice break up and subsequent spring flooding, coastal and shoreline erosion, thaw slumping, and degradation of ice rich deposits. Deltaic sediments also tend to be highly susceptible to ground-ice aggradation, making them more ice-rich than adjacent nondeltaic landscapes. In addition, Arctic deltas will be severely affected by global climate change through sea level rise, lengthened thaw season, changing river discharge, storm surge flooding and thawing permafrost. We are therefore at risk, to face reactivation of millennia-old soil carbon and nitrogen deposits by the degradation of previously permanently frozen river delta deposits. However, there is a lack of studies on Arctic deltas and only very coarse estimates on Arctic delta carbon and nitrogen stocks exist. Here we present a new data-set of 140 soil cores, including more than 1400 samples from 17 different deltas spread across the Arctic. We combine new and legacy soil core data to estimate for the first time pan-Arctic deltaic carbon and nitrogen stocks and close a knowledge gap for deep permafrost stock estimations. We found that Arctic deltas present a significant pool for organic carbon and nitrogen, thus their change poses risks far beyond the Arctic. Permafrost thaw in such dynamic landscapes will increase nutrient transport from land to ocean with implications on Arctic near-shore zones (e.g. affecting foodwebs and biogeochemical processes) as well as increased greenhouse gas release due to large amounts of carbon and nitrogen becoming available from previously frozen ground. Our study highlights the need to better understand dynamic processes in Arctic deltas, since these vulnerable carbon and nitrogen rich deposits will be severely affected by the effects of global climate change.

Description: 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 thaw. Despite widespread permafrost degradation during the past 40 years, 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 sparse. 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.

Description: 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.

Description: Soils and other unconsolidated deposits in the northern circumpolar permafrost region store large amounts of soil organic carbon (SOC). This SOC is potentially vulnerable to remobilization following soil warming and permafrost thaw, but stock estimates are poorly constrained and quantitative error estimates were lacking. This study presents revised estimates of the permafrost SOC pool, including quantitative uncertainty estimates, in the 0–3 m depth range in soils as well as for deeper sediments (〉 3 m) in deltaic deposits of major rivers and in the Yedoma region of Siberia and Alaska. The revised estimates are based on significantly larger databases compared to previous studies. Compared to previous studies, the number of individual sites/pedons has increased by a factor ×8–11 for 1–3 m soils, a factor ×8 for deltaic alluvium and a factor ×5 for Yedoma region deposits. A total estimated mean storage for the permafrost region of ca. 1300–1400 Pg with an uncertainty range of 1050–1650 Pg encompasses the revised estimates. Of this, ≤900 Pg is perennially frozen. While some components of the revised SOC stocks are similar in magnitude to those previously reported for this region, there are also substantial differences in individual components. There is evidence of substantial remaining regional data-gaps. Estimates remain particularly poorly constrained for soils in the High Arctic region and physiographic regions with thin sedimentary overburden (mountains, highlands and plateaus) as well as for 〉3 m depth deposits in deltas and the Yedoma region.

Description: High latitude terrestrial ecosystems are key components in the global carbon (C) cycle. The Northern Circumpolar Soil Carbon Database (NCSCD) was developed to quantify stocks of soil organic carbon (SOC) in the northern circumpolar permafrost region (18.7×106 km2 5 ). The NCSCD is a digital Geographical Information systems (GIS) database compiled from harmonized regional soil classification maps, in which data on soil coverage has been linked to pedon data from the northern permafrost regions. Previously, the NCSCD has been used to calculate SOC content (SOCC) and mass (SOCM) to the reference depths 0–30 cm and 0–100 cm (based on 1778 pedons). It 10 has been shown that soils of the northern circumpolar permafrost region also contain significant quantities of SOC in the 100–300 cm depth range, but there has been no circumpolar compilation of pedon data to quantify this SOC pool and there are no spatially distributed estimates of SOC storage below 100 cm depth in this region. Here we describe the synthesis of an updated pedon dataset for SOCC in deep soils 15 of the northern circumpolar permafrost regions, with separate datasets for the 100– 200 cm (524 pedons) and 200–300 cm (356 pedons) depth ranges. These pedons have been grouped into the American and Eurasian sectors and the mean SOCC for different soil taxa (subdivided into Histels, Turbels, Orthels, Histosols, and permafrost-free mineral soil taxa) has been added to the updated NCSCDv2. The updated version of 20 the database is freely available online in several different file formats and spatial resolutions that enable spatially explicit usage in e.g. GIS and/or terrestrial ecosystem models. The potential applications and limitations of the NCSCDv2 in spatial analyses are briefly discussed. An open access data-portal for all the described GIS-datasets is available online at: http://dev1.geo.su.se/bbcc/dev/v3/ncscd/download.php. The NC25 SCDv2 database has the doi:10.5879/ECDS/00000002.

Description: The current estimate of the soil organic carbon (SOC) pool in the northern permafrost region of 1672 Petagrams (Pg),C is much larger than previously reported and needs to be incorporated in global soil carbon (C) inventories. The Northern Circumpolar Soil Carbon Database (NCSCD), extended to include the range 0–300 cm, is now available online for wider use by the scientific community. An important future aim is to provide quantitative uncertainty ranges for C pool estimates. Recent studies have greatly improved understanding of the regional patterns, landscape distribution and vertical (soil horizon) partitioning of the permafrost C pool in the upper 3m of soils. However, the deeper C pools in unconsolidated Quaternary deposits need to be better constrained. A general lability classification of the permafrost C pool should be developed to address potential C release upon thaw. The permafrost C pool and its dynamics are beginning to be incorporated into Earth System models, although key periglacial processes such as thermokarst still need to be properly represented to obtain a better quantification of the full permafrost C feedback on global climate change.

Description: The current estimate for soil organic carbon (SOC) quantity in the northern circumpolar permafrost region (Tarnocai et al., 2009) is 191 Pg for topsoil (0–30 cm depth), 496 Pg for the upper 100 cm of soil and SOC mass to 300 cm soil depth is estimated to be 1024 Pg. In addition, storage in deeper (〉 300 cm) Yedoma deposits (407 Pg) and deltaic deposits (241 Pg) brings the total estimate to 1672 Pg, of which 1466 Pg is stored in perennially frozen ground. The estimate for 0–1 m depth SOC mass is based on the Northern Circumpolar Soil Carbon Database (NCSCD), a geospatial database which links 1647 pedons from the northern permafrost regions to several digitized regional/national soil maps with a combined circumpolar coverage. This database has recently been published online and the data is available in several different file formats, including gridded files with different spatial resolutions. Files adapted for use in GIS or modeling applications (shape-files, TIFF-rasters and NetCDF files) are available for separate regions or with merged circumpolar coverage. Estimates for the 0–30 cm and 0–100 cm depth ranges based on the NCSCD are unlikely to be significantly changed or refined in the coming years. However, the emergence of high quality geospatial datasets with circumpolar coverage as well as applications of spatially distributed regression/kriging techniques in periglacial environments (e.g. Mishra and Riley, 2012) point towards complementary approaches that may significantly increase our knowledge of circumpolar SOC distribution. The present estimates of SOC mass in the 0–300 cm depth range is based on very limited field data (46 Canadian pedons), is accorded low to very low confidence and is not included in the spatially distributed NCSCD (Tarnocai et al., 2009). However, a compilation of additional pedon data is underway and an updated version of the NCSCD will be complemented with spatially distributed estimates of 100–200 cm and 200–300 cm depth SOCM based on 〉 200 deep pedons from around the circumpolar region. This estimate is also planned to include quantification of upscaling uncertainties caused by insufficient field sampling of naturally variable soils and areal misrepresentation of soil types in the maps used for upscaling (following Hugelius, 2012). Hugelius, G. (2012), Spatial upscaling using thematic maps: An analysis of uncertainties in permafrost soil carbon estimates, Global Biogeochem. Cycles, 26, GB2026, doi:10.1029/2011GB004154 Mishra U. and Riley W.J. (2012) Alaskan soil carbon stocks: spatial variability and dependence on environmental factors, Biogeosciences Discuss, 9, 5695–5718

Description: Permafrost soils were characterized first in the field by numerous investigators according to standard soil descriptions and were sampled by depth increment within soil horizon boundaries. Measures of bulk density, C, N, and pH were used to further characterize C and N storage for soil horizons and profiles. Field attributes for organic (Oi, Oe, Oa or L, F, H) horizons, mineral (A, E, B, C) horizons, cryoturbated (jj subscripts with mixtures of organic and mineral matrices), and gleying (subscript g with reduced colors), ice-rich layers (e.g., Wf/Cgfjj, Wf/Oafjj) were examined for differences in C, N, and bulk density. Using the Community Climate System Model (CCSM4) we calculated cumulative distributions of active layer thickness (ALT) under current and future climates. We then superposed physical state over soil horizons to explore how chemical attributes are exposed by progressive thaw. Thawing will likely expose 147 Pg of C with 10 Pg of N by 2050 (representative concentration pathway RCP scenario 4.5) and as much as 436 PgC with 29 PgN by 2100 (RCP 8.5). This represents about 30% and 80% of circumarctic permafrost carbon for yr 2050 (RCP 4.5) and yr 2100 (RCP 8.5) scenarios, respectively. Organic horizons will likely contribute the earliest pulse of CO2 via combustion and decomposition. These changes have the potential for strong additional loading to our atmosphere, water resources, and ecosystems.