Multiple thermokarst lake generations in an 11,800-year-old permafrost core on the northern Seward Peninsula, Alaska
Josefine Lenz, Sebastian Wetterich, Benjamin M. Jones, Hanno Meyer, Anatoly Bobrov & Guido Grosse
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.
Patterns and rates of riverbank erosion involving ice-rich permafrost (yedoma) in northern Alaska
Mikhail Kanevskiy, Yuri Shur, Jens Strauss, Torre Jorgenson, Daniel Fortier, Eva Stephani, Alexander Vasiliev
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.
Tundra fires destabilize permafrost
Benjamin M. Jones, Guido Grosse, Christopher D. Arp, Eric Miller, Lin Liu, Daniel J. Hayes & Christopher F. Larsen
Nature, Scientific Reports 5, Article number: 15865 (2015) doi:10.1038/srep15865
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.
A simplified, data-constrained approach to estimate the permafrost carbon-climate feedback
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.
Climate change and the permafrost carbon feedback
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.
Organic-matter quality of deep permafrost carbon
J. Strauss, L. Schirrmeister, K. Mangelsdorf, L. Eichhorn, S. Wetterich, and U. Herzschuh
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.
The disappearing East Siberian Arctic island Muostakh
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.
Observation-based modelling of permafrost carbon fluxes
T. Schneider von Deimling, G. Grosse, J. Strauss, L. Schirrmeister, A. Morgenstern, S. Schaphoff, M. Meinshausen, and J. Boike
Biogeosciences Discussions 11(12): 16599-16643
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.
Mid-Wisconsin to Holocene permafrost and landscape dynamics based on a drained lake basin core from the northern Seward Peninsula, Northwest Alaska.
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.
Quantifying Wedge-Ice Volumes in Yedoma and Thermokarst Basin Deposits
M. Ulrich, G. Grosse, J. Strauss, and L. Schirrmeister
Permafrost and Periglacial Processes, 25(3), 151-161. doi:10.1002/ppp.1810
Abstract. Wedge-ice volume (WIV) is a key factor in assessing the response of ice-rich permafrost landscapes to thaw and in quantifying deep permafrost soil carbon inventories. Here, we present a method for calculating WIV in late Pleistocene Yedoma deposits andHolocene thermokarst basin deposits at four study areas in Siberia and Alaska. Ice-wedge polygons and thermokarst mound (baydzherakh) patterns were mapped on different landscape units using very high-resolution (0.5 m/pixel) satellite imagery (WorldView-1 and GeoEye-1). 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 WIV between the study sites and within certain terrain units. Calculated maximum WIV ranges from 31.4 to 63.2 vol% for Yedoma deposits and from 6.6 to 13.2 vol% for thermokarst basin deposits.
Estimated stocks of circumpolar permafrost carbon
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
Biogeosciences, 11, 6573-6593. doi:10.5194/bg-11-6573-2014
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.