Top: LCC for IKP (a) & FCR delta (b) based on Landsat 8 land cover classification. Middle: Size of land cover class areas for IKP (c) & FCR (d) delta. Bottom: Total river delta SOC (in Tg C) separated into land cover classes for IKP (e) & FCR (f) delta. (Photo: Matthias Fuchs)
Matthias Fuchs, Guido Grosse, Benjamin M. Jones, Jens Strauss, Carson A. Baughman, Donald A. Walker
Abstract: Arctic river deltas are highly dynamic environments in the northern circumpolar permafrost region that are affected by fluvial, coastal, and permafrost-thaw processes. They are characterized by thick sediment deposits containing large but poorly constrained amounts of frozen organic carbon and nitrogen. This study presents new data on soil organic carbon and nitrogen storage as well as accumulation rates from the Ikpikpuk and Fish Creek river deltas, two small, permafrost-dominated arctic river deltas on the Arctic Coastal Plain of northern Alaska. A soil organic carbon storage of 42.4 kg C m-2 and 37.9 kg C m-2 and soil nitrogen storage of 2.1 kg N m-2 and 2.0 kg N m-2 was found for the first two meters of soil for the Ikpikpuk and Fish Creek river delta, respectively. While the upper meter of soil contains 3.57 Tg C, substantial amounts of carbon (3.09 Tg C or 46%) are also stored within the second meter of soil (100 – 200 cm) in the two deltas. An increasing and inhomogeneous distribution of C with depth is indicative of the dominance of deltaic depositional rather than soil forming processes for soil organic carbon storage. Largely mid- to late Holocene radiocarbon dates in our cores suggest different carbon accumulation rates for the two deltas for the last 2000 years. Rates up to 28 g C m-2 yr-1 for the Ikpikpuk river delta are about twice as high as the Fish Creek river delta. With this study, we highlight the importance of including these highly dynamic permafrost environments in future permafrost carbon estimations.
Top: Land form classification of Sobo-Sise Island and Bykovsky Peninsula. Bottom: Mean soil organic carbon (kg C m-2) storage in thermokarst and yedoma upland deposits on Sobo-Sise Island and Bykovsky Peninsula. (Graphic: Alfred-Wegener-Institut)
Matthias Fuchs, Guido Grosse, Jens Strauss, Frank Günther, Mikhail Grigoriev, Georgy M. Maximov, Gustaf Hugelius
Summary: Ice-rich yedoma-dominated landscapes store considerable amounts of organic carbon (C) and nitrogen (N) and are vulnerable to degradation under climate warming. We investigate the C and N pools in two thermokarst-affected yedoma landscapes – on Sobo-Sise Island and on Bykovsky Peninsula in the north of eastern Siberia. Soil cores up to 3 m depth were collected along geomorphic gradients and analysed for organic C and N contents. A high vertical sampling density in the profiles allowed the calculation of C and N stocks for short soil column intervals and enhanced understanding of within-core parameter variability. Profile-level C and N stocks were scaled to the landscape level based on landform classifications from 5 m resolution, multispectral RapidEye satellite imagery.
Mean landscape C and N storage in the first metre of soil for Sobo-Sise Island is estimated to be 20.2 kg C m−2 and 1.8 kg N m−2 and for Bykovsky Peninsula 25.9 kg C m−2 and 2.2 kg N m−2. Radiocarbon dating demonstrates the Holocene age of thermokarst basin deposits but also suggests the presence of thick Holocene-age cover layers which can reach up to 2 m on top of intact yedoma landforms. Reconstructed sedimentation rates of 0.10–0.57 mm yr−1 suggest sustained mineral soil accumulation across all investigated landforms. Both yedoma and thermokarst landforms are characterized by limited accumulation of organic soil layers (peat). We further estimate that an active layer deepening of about 100 cm will increase organic C availability in a seasonally thawed state in the two study areas by ∼ 5.8 Tg (13.2 kg C m−2). Our study demonstrates the importance of increasing the number of C and N storage inventories in ice-rich yedoma and thermokarst environments in order to account for high variability of permafrost and thermokarst environments in pan-permafrost soil C and N pool estimates.
Permafrost carbon in comparison with other terrestrial carbon stocks and the atmosphere, modified from Strauss et al. (2017)
Jens Strauss, Lutz Schirrmeister, Guido Grosse, Daniel Fortier, Gustaf Hugelius, Christian Knoblauch, Vladimir Romanovsky, Christina Schädel, Thomas Schneider von Deimling, Edward A. G. Schuur, Denis Shmelev, Mathias Ulrich, Alexandra Veremeeva
Summary: Permafrost is a distinct feature of the terrestrial Arctic and is vulnerable to climate warming. Permafrost degrades in different ways, including deepening of a seasonally unfrozen surface and localized but rapid development of deep thaw features. Pleistocene ice-rich permafrost with syngenetic ice-wedges, termed Yedoma deposits, are widespread in Siberia, Alaska, and Yukon, Canada and may be especially prone to rapid-thaw processes. Freeze-locked organic matter in such deposits can be re-mobilized on short time-scales and contribute to a carbon-cycle climate feedback. Here we synthesize the characteristics and vulnerability of Yedoma deposits by synthesizing studies on the Yedoma origin and the associated organic carbon pool. We suggest that Yedoma deposits accumulated under periglacial weathering, transport, and deposition dynamics in non-glaciated regions during the late Pleistocene until the beginning of late glacial warming. The deposits formed due to a combination of aeolian, colluvial, nival, and alluvial deposition and simultaneous ground ice accumulation. We found up to 130 gigatons organic carbon in Yedoma, parts of which are well-preserved and available for fast decomposition after thaw. Based on incubation experiments, up to 10% of the Yedoma carbon is considered especially decomposable and may be released upon thaw. The substantial amount of ground ice in Yedoma makes it highly vulnerable to disturbances such as thermokarst and thermo-erosion processes. Mobilization of permafrost carbon is expected to increase under future climate warming. Our synthesis results underline the need of accounting for Yedoma carbon stocks in next generation Earth-System-Models for a more complete representation of the permafrost-carbon feedback.
Summary: Lakes are a ubiquitous landscape feature in northern permafrost regions. They have a strong impact on carbon, energy and water fluxes and can be quite responsive to climate change. The monitoring of lake change in northern high latitudes, at a sufficiently accurate spatial and temporal resolution, is crucial for understanding the underlying processes driving lake change. To date, lake change studies in permafrost regions were based on a variety of different sources, image acquisition periods and single snapshots, and localized analysis, which hinders the comparison of different regions. Here, we present a methodology based on machine-learning based classification of robust trends of multi-spectral indices of Landsat data (TM, ETM+, OLI) and object-based lake detection, to analyze and compare the individual, local and regional lake dynamics of four different study sites (Alaska North Slope, Western Alaska, Central Yakutia, Kolyma Lowland) in the northern permafrost zone from 1999 to 2014.
Regional patterns of lake area change on the Alaska North Slope (−0.69%), Western Alaska (−2.82%), and Kolyma Lowland (−0.51%) largely include increases due to thermokarst lake expansion, but more dominant lake area losses due to catastrophic lake drainage events. In contrast, Central Yakutia showed a remarkable increase in lake area of 48.48%, likely resulting from warmer and wetter climate conditions over the latter half of the study period.
Within all study regions, variability in lake dynamics was associated with differences in permafrost characteristics, landscape position (i.e., upland vs. lowland), and surface geology. With the global availability of Landsat data and a consistent methodology for processing the input data derived from robust trends of multi-spectral indices, we demonstrate a transferability, scalability and consistency of lake change analysis within the northern permafrost region.
Minimum, mean (red), and maximum ground temperatures based on almost 3 years continuous measurements (from 11 May 2012 to 27 April 2015) (Photo: Alfred-Wegener-Institut)
Lutz Schirrmeister, Georg Schwamborn, Pier Paul Overduin, Jens Strauss, Margret C. Fuchs, Mikhail Grigoriev, Irina Yakshina, Janet Rethemeyer, Elisabeth Dietze, and Sebastian Wetterich
Summary: In this study, we investigate late Pleistocene permafrost at the western coast of the Buor Khaya Peninsula in the south-central Laptev Sea (Siberia). Two Yedoma exposures and one drill core were studied for cryolithological, geochemical, and geochronological parameters. The deposition of the Yedoma, as revealed by radiocarbon dates of sedimentary organic matter, took place between 54.1 and 30.1 kyr BP. Continued Yedoma deposition until about 14.7 kyr BP is shown by dates from organic matter preserved in ice-wedge ice. For the lowermost and oldest Yedoma part, infrared-stimulated luminescence dates on feldspar show deposition ages between 51.1 ± 4.9 and 44.2 ± 3.6 kyr BP. The cryolithological inventory of the Yedoma IC preserved on the Buor Khaya Peninsula is closely related to the results of other studies, for example, to the west on the Bykovsky Peninsula, where formation time and formation conditions were similar. Due to intense coastal erosion, the biogeochemical signature of the studied Yedoma IC represents the terrestrial end-member, and is closely related to organic matter currently being deposited in the marine realm of the Laptev Sea shelf.
Position of the Buor Khaya Peninsula in the Siberian Arctic (a). Buor Khaya Peninsula study site in northeastern Siberia (b), and location of the drill site, marked with back star (c) (Photo: Alfred-Wegener-Institut)
Stapel, J. G., L. Schirrmeister, P. P. Overduin, S. Wetterich, J. Strauss, B. Horsfield, and K. Mangelsdorf
A permafrost core from a peninsula in northern Siberia comprising deposits of Late Pleistocene to Early Holocene age has been investigated to characterize living and past microbial communities with respect to modern and paleoclimate environmental conditions, and to evaluate the potential of the organic matter for greenhouse gas generation. Microbial life markers - intact phospholipids and phospholipid fatty acids - are found throughout the entire core and indicate the presence of living microorganisms also in older permafrost deposits. The data suggest that organic matter stored in the permafrost deposits is not different in terms of organic matter quality than the fresh surface organic material. Considering the expected increase of permafrost thaw due to climate warming, this implies a potentially strong impact on greenhouse gas generation from permafrost areas in future with positive feedback on climate variation.
Regional overview of decadal trend slope of multi-spectral indices (TCB, TCG, TCW, NDVI, NDMI, NDWI). (Photo: Alfred-Wegener-Institut)
Ingmar Nitze, Guido Grosse
Remote Sensing of Environment, Volume 181, August 2016, Pages 27–41, doi.10.1016/j.rse.2016.03.038
In our paper we present a methodology to detect landscape changes in the Arctic Lena Delta with remote sensing time-series. We used the entire Landsat archive to calculate trends of different surface properties like vegetation, moisture or albedo, which can be related to specific land surface processes. The methodology was applied on the entire Lena Delta (~ 30,000 km²) where we identified several processes of different spatial and temporal scales since the year 1999. Examples of regional scale processes include greening and wetting in the predominantly active parts of the Lena Delta. More local scale dynamics like thermokarst lake drainage or expansion, fluvial morphodynamics, and coastal dynamics were also identified.
Summary: Permafrost degradation influences the morphology, biogeochemical cycling and hydrology of Arctic landscapes over a range of time scales. To reconstruct temporal patterns of early to late Holocene permafrost and thermokarst dynamics, a 350-cm-long permafrost core from a drained lake basin on the northern Seward Peninsula, Alaska, was analyzed by applying methods of micropaleontology, sedimentology, geochemistry, as well as radiocarbon dating and stable water isotopes of intra-sedimentary ice.
For the first time, several distinct thermokarst lake phases were reconstructed from a lake sediment core. These include a pre-lacustrine environment characterized by the Devil Mountain Maar tephra (22.8 ± 0.3 cal ka BP), which has vertically subsided in places due to subsequent development of a deep thermokarst lake that initiated around 11.8 cal ka BP (Grandma Rhonda). At about 9.0 cal ka BP this lake transitioned from a stable depositional environment to a very dynamic lake system (Mama Rhonda). Complete drainage of this lake occurred at 1.1 cal ka BP, including post-drainage sediment freezing from the top down and gradual accumulation of terrestrial peat, as well as uniform upward talik refreezing.
This core-based reconstruction improves our understanding of biogeochemical cycles in thermokarst-affected regions of the Arctic.
Summary: Yedoma permafrost is vulnerable to thermal degradation and erosion because of the extremely high ice contents. This degradation can result in significant surface subsidence and retreat of coastal bluffs and riverbanks with large consequences to landscape evolution, infrastructure damage, and water quality. We used remote sensing and field observations to assess patterns and rates of riverbank erosion at a 35-m-high active yedoma bluff along the Itkillik River in northern Alaska.Active riverbank erosion show at retreat of the riverbank during 1995 - 2010 within different segments of the bluff varied from 180 to 280 m. The average retreat rate for the most actively eroded part of the riverbank was almost 19 m/y. This study reports the highest long-term rates of riverbank erosion ever observed in permafrost regions of Eurasia and North America.
Comparison between the two airborne LiDAR datasets showing clear permafrost terrain subsidence a few years after a large and severe Arctic tundra fire (Photo: Alfred Wegener Institut)
Benjamin M. Jones, Guido Grosse, Christopher D. Arp, Eric Miller, Lin Liu, Daniel J. Hayes & Christopher F. Larsen
Summary: Tundra fires in the Arctic can have a destabilization effect on ice-rich permafrost.Using airborne laserscan data, the new studies demonstrates that significant land surface subsidence occurred just a few years after the 1000km2 large fire on the Alaska North Slope in 2007. The subsidence is associated with melting ground ice, which apparently is a long-term impact of intense tundra fires that damage vegetation and soil organic layers which usually act as protecting layers for permafrost against a warming atmosphere. The remote sensing data shows that about 34% of the land surface subsided (sometimes in excess of 1m) just a few years after the fire and the polygonal micro-topography has increased. The resulting multiple feedbacks with snow distribution, hydrology, and vegetation eventually lead to increased thermokarst formation.
Maps of fractional C losses over the period 2010–2100 calculated by the PInc-PanTher scaling approach at four depths and two warming scenarios using CLM4.5 soil temperatures as an example driving soil climate dataset. (Photo: Alfred Wegener Institut)
D. Koven, E. A. G. Schuur, C. Schädel, T. J. Bohn, E. J. Burke, G. Chen, X. Chen, P. Ciais, G. Grosse, J. W. Harden, D. J. Hayes, G. Hugelius, E. E. Jafarov, G. Krinner, P. Kuhry, D. M. Lawrence, A. H. MacDougall, S. S. Marchenko, A. D. McGuire, S. M. Natali, D. J. Nicolsky, D. Olefeldt, S. Peng, V. E. Romanovsky, K. M. Schaefer, J. Strauss, C. C. Treat and M. Turetsky
Philosophical Transactions of the Royal Society A, doi:10.1098/rsta.2014.0423
Summary: Permafrost is expected to lose carbon to the atmosphere in response to global warming, as increased soil temperatures lead to faster decomposition of old organic matter that is currently frozen in the ground. We construct a model of permafrost soil carbon losses using multiple estimates of permafrost thermal dynamics, soil C stocks, and the response of permafrost soil carbon to experimental warming. Our results show that the magnitude of the feedback from thawing permafrost is a substantial fraction of the total global amount, and will play an important role in determining the amount of warming that accompanies fossil fuel release.
E. A. G. Schuur, A. D. McGuire, C. Schädel, G. Grosse, J. W. Harden, D. J. Hayes, G. Hugelius, C. D. Koven, P. Kuhry, D. M. Lawrence, S. M. Natali, D. Olefeldt, V. E. Romanovsky, K. Schaefer, M. R. Turetsky, C. C. Treat & J. E. Vonk
Nature, 520, 171-179. doi:10.1038/nature14338
Summary: Large quantities of organic carbon are stored in frozen soils (permafrost) within Arctic and sub-Arctic regions. A warming climate can induce environmental changes that accelerate the microbial breakdown of organic carbon and the release of the greenhouse gases carbon dioxide and methane. This feedback can accelerate climate change, but the magnitude and timing of greenhouse gas emission from these regions and their impact on climate change remain uncertain. Here we find that current evidence suggests a gradual and prolonged release of greenhouse gas emissions in a warming climate and present a research strategy with which to target poorly understood aspects of permafrost carbon dynamics.
Summary: Climatic warming is affecting permafrost, including the decomposition of so far freeze-locked organic matter. However, quantitative data for the quality of the organic matter stored in permafrost and its availability for decomposition is limited. We analyzed the quality of organic matter in late Pleistocene (Yedoma) and Holocene (thermokarst) deposits. A lack of depth trends reveals a constant quality of organic matter showing that permafrost acts like a freezer, preserving the quality of the organic matter. This organic matter will be susceptible to microbial decomposition under climatic warming and emitting greenhouse gases.
seasonal thermo-denudation (Photo: Alfred Wegener Institut)
F. Günther, P. P. Overduin, I. A. Yakshina, T. Opel, A. V. Baranskaya, and M. N. Grigoriev
The Cryosphere, 9, 151-178, 2015. doi:10.5194/tc-9-151-2015
Summary: Coastal erosion rates at Muostakh Island (Siberian Arctic) have doubled recently, based on remotely sensed observations of land loss, and the island will disappear prematurely. Thermo-erosion increases by 1.2 m per year when summer temperature warms by 1 °C, based on analyses of seasonal variability of permafrost thaw. Due to rapid permafrost thaw, the land surface is subsiding up to 11 cm per year, based on comparison of elevation changes and active layer thaw depth.
Summary: Permafrost soils store vast amounts of organic carbon deep-frozen in the ground. In our modelling study we calculate the magnitude and timing of carbon fluxes which result from microbial decomposition of newly thawed organic matter after permafrost degradation. Finally, we estimate the additional global warming arising from the permafrost carbon climate feedback.
Lenz J., Grosse G., Jones B.M., Walter Anthony K.M., Bobrov A, Wulf S., Wetterich S.
Permafrost and Periglacial Processes, DOI: 10.1002/ppp.1848
Summary: Permafrost-related processes drive regional landscape dynamics in the Arctic terrestrial system. A better understanding of past periods indicative of permafrost degradation and aggradation is important for predicting the future response of Arctic landscapes to climate change. Here, we used a multi-proxy approach to analyse a ~ 4 m long sediment core from a drained thermokarst lake basin on the northern Seward Peninsula in western Arctic Alaska (USA). Sedimentological, biogeochemical, geochronological, micropalaeontological (ostracoda, testate amoebae) and tephra analyses were used to determine the long-term environmental Early-Wisconsin to Holocene history preserved in our core for central Beringia. Yedoma accumulation dominated throughout the Early to Late-Wisconsin but was interrupted by wetland formation from 44.5 to 41.5 ka BP. The latter was terminated by the deposition of 1 m of volcanic tephra, most likely originating from the South Killeak Maar eruption at about 42 ka BP. Yedoma deposition continued until 22.5 ka BP and was followed by a depositional hiatus in the sediment core between 22.5 and 0.23 ka BP. We interpret this hiatus as due to intense thermokarst activity in the areas surrounding the site, which served as a sediment source during the Late-Wisconsin to Holocene climate transition. The lake forming the modern basin on the upland initiated around 0.23 ka BP and drained catastrophically in spring 2005.
The present study emphasises that Arctic lake systems and periglacial landscapes are highly dynamic and that permafrost formation as well as degradation in central Beringia was controlled by regional to global climate patterns as well as by local disturbances.
M. Ulrich, G. Grosse, J. Strauss, and L. Schirrmeister
Permafrost and Periglacial Processes, 25(3), 151-161. doi:10.1002/ppp.1810
Summary: Wedge-ice volume is a key factor for the response of ice-rich permafrost landscapes to thaw and in for quantifying deep permafrost soil carbon inventories. Here, we present a method for calculating wedge-ice volume in Yedoma deposits and thermokarst basin deposits at four study areas in Siberia and Alaska. Ice-wedge polygons and thermokarst mound patterns were mapped on different landscape units using very high-resolution (0.5 m/pixel) satellite imagery. In a geographic information system (GIS) environment, Thiessen polygons were automatically created to reconstruct relict ice-wedge polygonal networks, and field and published data on ice-wedge dimensions were used to generate three-dimensional subsurface models that distinguish between epi- and syngenetic ice-wedge geometry. The results reveal significant variations in wedge-ice volume between the study sites and within certain terrain units. Calculated maximum wedge-ice volume ranges from 31.4 to 63.2 vol% for Yedoma deposits and from 6.6 to 13.2 vol% for thermokarst basin deposits.
Map of estimated 0–3 m SOC storage (kg C m−²) in the northern circumpolar permafrost region (Photo: Alfred Wegener Institut)
G. Hugelius, J. Strauss, S. Zubrzycki, J. W. Harden, E. A. G. Schuur, C.-L. Ping, L. Schirrmeister, G. Grosse, G. J. Michaelson, C. D. Koven, J. A. O’Donnell, B. Elberling, U. Mishra, P. Camill, Z. Yu, J. Palmtag, and P. Kuhry
Summary: This study provides an updated estimate of organic carbon stored in the northern permafrost region. The study includes estimates for carbon in soils (0 to 3 m depth) and deeper sediments in river deltas and the Yedoma region. We find that field data is still scarce from many regions. Total estimated carbon storage is ~1300 Pg with an uncertainty range of between 1100 and 1500 Pg. Around 800 Pg carbon is perennially frozen, equivalent to all carbon dioxide currently in the Earth's atmosphere.
