2019055898 Knight, Jasper (University of the Witwatersrand, School of Geography, Archaeology & Environmental Studies, Johannesburg, South Africa). A new model of rock glacier dynamics: Geomorphology, 340, p. 153-159, illus. incl. 1 table, 75 ref., September 2019.
Rock glaciers have traditionally been described as periglacial landforms and thus associated genetically with the presence of permafrost and a seasonal active layer. They have also been described as glacigenic in origin, in which the main rock glacier body contains glacier ice at depth. Other rock glaciers can be considered as relict where they contain no interstitial ice and are functionally inactive. Although all rock glaciers are to some extent polygenic, there is no clear, simple test that can be used to distinguish between different rock glacier types. This study proposes a simple and testable model for rock glacier classification based on their behaviour from evidence reported from the literature. The study then proposes an interpretive evolutionary model describing the temporal evolution of rock glacier surface movement through the year that can inform on its dynamical controls. This analysis provides an easily-deployed interpretive framework for the origins of rock glaciers.
2019055888 Lin Zhanju (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, State Key Laboratory of Frozen Soil Engineering, Lanzhou, China); Gao Zeyong; Niu Fujun; Luo Jing; Yin Guoan; Liu Minghao and Fan Xingwen. High spatial density ground thermal measurements in a warming permafrost region, Beiluhe Basin, Qinghai-Tibet Plateau: Geomorphology, 340, p. 1-14, illus. incl. 7 tables, geol. sketch maps, 52 ref., September 2019.
Air, ground surface, and permafrost surface temperatures are important components of the permafrost thermal regime. However, ground temperatures from one or two boreholes are commonly considered representative of site conditions in permafrost studies despite significant variations in local surface conditions. This makes the evaluation of site-scale temperature variations important for improving the accuracy of permafrost modelling efforts. In this study we analyzed the variability in near-surface ground temperatures in a warming permafrost region using high spatial density borehole measurements to capture variations in surface conditions. Ground temperatures were collected from 72 boreholes drilled to 5 m depth at 8 sites in Beiluhe Basin, Qinghai-Tibet Plateau. Six sites straddled an alpine meadow ecotone between well- and sparsely-vegetated ground, and two sites were located on slopes with opposing aspects. Air temperatures at the 8 sites were similar with annual mean values ranging from -2.6 to -3.0°C in 2016-18. In contrast, annual mean surface temperatures exhibited greater variation between sites, so that surface offsets were also variable. Ground surface temperatures were highest at a sloping sunny site, and lowest at a north-facing shady site. The results indicated that surface temperatures were strongly controlled by slope aspect. In contrast, the expected effect of vegetation cover shading was not distinguishable because of variations in soil moisture content between sites. Deeper temperatures at the permafrost surface and at 5 m depth exhibited a similar trend among sites except in an unusual warm transitional area where eolian erosion disturbed the surface vegetation cover. The detailed ground temperature records characterizing within- and between-site variations could be used in future to support the calibration and validation of numerical models of permafrost distribution.
2019055894 Pandey, Pratima (Indian Institute of Remote Sensing, Geosciences Department, Dehradun, India). Inventory of rock glaciers in Himachal Himalaya, India using high-resolution Google Earth imagery: Geomorphology, 340, p. 103-115, illus. incl. 2 tables, sketch maps, 81 ref., September 2019.
Little information about the number, spatial distribution, and characteristics of rock glaciers in Himachal Himalaya is available. This information is crucial to assess the hydrological contribution of permafrost regimes and to understand its response to changing climate. Employing high-resolution satellite data freely accessible through Google Earth, the first comprehensive rock glacier inventory of Himachal Himalaya is presented in this work. The inventory reports 516 rock glaciers in the study area corresponding to an estimated area of 353 km2 of which 59% have glacier origin and 41% have talus origin. The frontal elevation of the lowest rock glacier in the Himachal Himalaya is 3052 m above sea level which was significantly low, whereas the highest rock glacier occurs at 5503 m above sea level. The mean minimum elevation of rock glaciers was 4484 m above sea level and the maximum was 4900 m above sea level. The majority of the rock glaciers have a northerly aspect (N, NE, NW) followed by westerly aspect signifying that slopes with lower potential incoming solar radiation favour the formation of rock glaciers. The mean annual surface temperature of the rock glaciers derived from Moderate Resolution Imaging Spectroradiometer (MODIS) Land surface temperature (LST) product (MOD11B3) was -1.5°C, with glacier-derived rock glaciers having colder surfaces than talus-derived rock glaciers. The topographical and climatological parameters greatly influenced the formation and development of rock glaciers.
2019055895 Patton, Annette I. (Colorado State University, Department of Geosciences, Fort Collins, CO); Rathburn, Sara L. and Capps, Denny M. Landslide response to climate change in permafrost regions: Geomorphology, 340, p. 116-128, illus. incl. 1 table, 142 ref., September 2019.
Rapid permafrost thaw in the high-latitude and high-elevation areas increases hillslope susceptibility to landsliding by altering geotechnical properties of hillslope materials, including reduced cohesion and increased hydraulic connectivity. This review synthesizes the fundamental processes that will increase landslide frequency and magnitude in permafrost regions in the coming decades with observational and analytical studies that document landslide regimes at high latitudes and elevations. We synthesize the available literature to address five questions of practical importance, which can be used to evaluate fundamental knowledge of landslide process and inform land management decisions to mitigate geohazards and environmental impacts. After permafrost thaws, we predict that landslides will be driven primarily by atmospheric input of moisture and freeze-thaw fracturing rather than responding to disconnected and perched groundwater, melting permafrost ice, and a plane of weakness between ground ice and the active layer. Transition between equilibrium states is likely to increase landslide frequency and magnitude, alter dominant failure styles, and mobilize carbon over timescales ranging from seasons to centuries. We also evaluate potential implications of increased landslide activity on local nutrient and sediment connectivity, atmospheric carbon feedbacks, and hazards to people and infrastructure. Last, we suggest three key areas for future research to produce primary data and analysis that will fill gaps in the existing understanding of landslide regimes in permafrost regions. These suggestions include 1) expand the geographic extent of English-language research on landslides in permafrost; 2) maintain or initiate long-term monitoring projects and aerial data collection; and 3) quantify the net effect on the terrestrial carbon budget.
2019062189 Lauzon, Rebecca (Los Alamos National Laboratory, Earth and Environmental Science Division, Los Alamos, NM); Piliouras, Anastasia and Rowland, Joel C. Ice and permafrost effects on delta morphology and channel dynamics: Geophysical Research Letters, 46(12), p. 6574-6582, illus., 37 ref., June 28, 2019.
Arctic regions are changing rapidly as permafrost thaws and sea ice retreats. These changes directly affect Arctic river deltas, but how permafrost and ice alter delta hydrology and sediment transport are not well researched. This knowledge gap limits our ability to forecast how these systems will respond to continued warming. We adapt the reduced complexity model of delta morphodynamics DeltaRCM to investigate the influences of permafrost and landfast ice on delta morphology and channel dynamics. We find that ice cover and permafrost decrease channel mobility, increase shoreline roughness, and route and deposit more sediment offshore. Ice cover also enhances overbank deposition, increasing subaerial delta elevations. Our modeling suggests that permafrost and ice loss in a warming climate could lead to less overbank and offshore deposition and more dynamic and spatially distributed fluxes of water and sediment across Arctic river deltas. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
2019059427 Weckwerth, Piotr (Nicolaus Copernicus University in Torun, Faculty of Earth Sciences, Torun, Poland); Gren, Katarzyna and Sobota, Ireneusz. Controls on downstream variation in surficial sediment size of an outwash braidplain developed under high Arctic conditions (Kaffioyra, Svalbard): Sedimentary Geology, 387, p. 75-86, illus. incl. 6 tables, sketch map, 105 ref., June 1, 2019.
The changes in morphology and surficial sediments of an outwash braidplain developed under high Arctic conditions are closely related to geomorphic processes, tectonic conditions and climate variations, and are affected by the existence of permafrost. These factors control the changes in river channel slope, their morphology and active braidplain width, which influence the downstream variation in grain size of outwash surficial sediments. Interdependence between these parameters has not previously been considered in relation to the spatial distribution of surficial sediments of outwash braidplain developed in the forefield of a retreating subpolar glacier. In this study, controls affecting the surficial lithology of the Waldemar River outwash (NW Spitsbergen, Svalbard) were recognised and indicated multiple correlations between the downstream changes in sediment texture, the geomorphometry of distributary channels, and outwash surface slope. Due to this, the techniques of multivariate regression modelling, artificial neural network and multivariate adaptive regression splines were used. Results show that observed relations between the sedimentary and morphological features indicate the existence of thresholds for downstream variation in bed material size which are not constant. Moreover, the processes of sediment transport in an outwash braidplain are strictly related to Shields stress, which is proportional to changes in braidplain slope, median grain diameter and sediment sorting in the proximal and middle zones of the outwash, but is inversely proportional to median grain diameter in the distal zone, contrary to Shields' bed-material threshold entrainment model. The results of this study will help understand outwash fan and plain evolution in paraglacial landscapes under conditions of changeable rate and source of sediment supply and transport capacity.
2019057838 Haq, M. Anul (NIIT University, Geographic Information Systems, Neemrana, India) and Baral, Prashant. Study of permafrost distribution in Sikkim Himalayas using Sentinel-2 satellite images and logistic regression modelling: Geomorphology, 333, p. 123-136, illus. incl. 10 tables, sketch maps, 58 ref., May 15, 2019.
In this study, Sentinel-2A (S-2A) Multi-Spectral Instrument (MSI) Level 1C (L1C) products are used for identification and mapping of rock glaciers within a transect under observation in Sikkim Himalayas. The mapped rock glaciers were classified on the basis of their activity (intact or relict) and their origin (glacier-derived or talus-derived). Logistic regression models were applied to calculate the probability of permafrost distribution within transect under observation. We observed that freely available high resolution S-2A MSI L1C products are a valuable addition to the already existing freely available high resolution satellite images that can be exploited to study rock glaciers in Himalayan region. The distribution of rock glaciers in Sikkim Himalayas is found to be strongly controlled by elevation and aspect. Topoclimatic conditions above 5000 m a.s.l. are favourable for the presence of permafrost in Sikkim Himalayas. More glacier-derived rock glaciers than talus-derived rock glaciers were observed within transect under observation. Outputs from logistic regression models were capable to reasonably estimate the spatially-distributed probability of permafrost occurrence in the region. However, outputs from these models depended upon the selection of the initiation line location points of rock glaciers and topoclimatic and topographic variables used as predictors for model computation. Based on probability distribution maps, more than 60% (>800 km2) area of transect under observation could contain permafrost. This high areal abundance of permafrost in Sikkim Himalayas suggests increased risks of thawing permafrost under the influence of climate warming in future.
2019061614 Hutchings, J. A. (University of Florida, Department of Geological Sciences, Gainesville, FL); Bianchi, T. S.; Kaufman, D. S.; Kholodov, A. L.; Vaughn, D. R. and Schuur, E. A. G. Millennial-scale carbon accumulation and molecular transformation in a permafrost core from interior Alaska: Geochimica et Cosmochimica Acta, 253, p. 231-248, illus. incl. sketch maps, 131 ref., May 15, 2019.
Organic carbon stored in high-latitude permafrost represents a potential positive feedback to climate warming as well as a valuable store of paleoenvironmental information. The below-freezing conditions have effectively removed permafrost organic material from the modern carbon cycle and preserved its pre-freezing bulk and molecular states. The conditions that lead to efficient burial of organic carbon (OC) within permafrost were investigated by measuring OC stocks, past accumulation rates, and biogeochemical composition of a permafrost core taken from Interior Alaska dating back to 40 ka. The post-glacial Marine Isotope Stage 1 is represented by the top 1.2 m of the core and contains 64.7 kg OC/m2 with an accumulation rate of 4.3 g OC/m2/yr. The sediments that accumulated around the Last Glacial Maximum contain 9.9 kg OC/m2 with an accumulation rate of 0.5 g OC/m2/yr. Carbon storage (144.7 kg OC/m2) and accumulation (26.1 g OC/m2/yr) are both observed to be greatest between 35 and 40 ka, late during the Marine Isotope Stage 3 global interstadial. The extent of OC degradation was assessed using lignin and amino acid biomarkers with both approaches indicating well-preserved contemporary active layer and interstadial OC, whereas stadial OC was highly degraded. Lignin compositional indices throughout the core appear altered by sorptive processes that confounded some expected trends in the overall organic matter composition, while amino acids provided a more integrated pattern of change. Significant correlations between carbon-normalized hydroxyproline and total lignin concentrations further support the usefulness of hydroxyproline as an indicator for the abundance of plant organic matter. A novel amino acid plant-microbial index of the ratio of microbial-specific muramic acid and diaminopimelic acid biomarkers to the plant-specific hydroxyproline biomarker, indicate a transition from plant-dominated organic matter in fresh organic soils (index values of 0.01-0.20) to more microbial-dominated organic matter in degraded mineral soils (index values of 0.50-2.50). The branched glycerol dialkyl glycerol tetraether composition is complex and is not immediately compatible with existing temperature transfer functions. Residence time within the active layer is interpreted to integrate key factors such as primary productivity, inorganic sediment delivery, and other climate factors that control soil organic matter degradation. The Marine Isotope Stage 3, mid-Wisconsin interstadial period at this locality was forest-dominated and suggests the currently prevailing tundra ecotone is sensitive to environmental change. The majority of buried permafrost OC is high in degradability and if thawed, would be expected to be highly vulnerable to microbial decomposition.
2019057922 Wang Fei (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Laboratory of Frozen Soil Engineering, Lanzhou, China); Li Guoyu; Ma Wei; Wu Qingbai; Serban, Mihaela; Samsonova, Vera; Fedorov, Alexandr; Jiang Ningshan and Wang Bo. Pipeline-permafrost interaction monitoring system along the China-Russia crude oil pipeline: Engineering Geology, 254, p. 113-125, illus. incl. sect., strat. col., 1 table, sketch map, 28 ref., May 2, 2019.
In-situ monitoring system is absolutely necessary for a long-distance linear pipeline infrastructure in permafrost regions due to the complicated interaction between buried pipeline and its harsh permafrost environment. To study this complex problem, a comprehensive in-situ monitoring system has been designed and established along the China-Russia Crude Oil Pipeline (CRCOP), which is one of vital energy channels for importing crude oil from Russia to China. This monitoring system can record the meteorological data, ground temperature and water content within the permafrost foundation, vertical settlement of the oil pipe, ground surface deformation on the pipeline right-of-way (on-ROW), as well as the thaw bulb around the pipeline at four sites with different engineering geological conditions. In this paper, the layout and instrumentation of the whole monitoring system and monitoring methods are described in detail, and then the thermal regime of permafrost on-ROW and off-ROW and cooling performance of the mitigative measures on foundation soils are evaluated. Results show that heat dissipated from the CRCOP lead to the rapid degradation of permafrost on-ROW and produce different sizes of thaw bulb around the oil pipelines. The mitigative measures, including insulation layer, two-phase closed thermosyphon and U-shaped air-ventilated pipes, are effective to minimize permafrost degradation and ensure the thermal stability of permafrost foundation along the CRCOP. Some recommendations are proposed for future research and for the monitoring system to be improved. This monitoring system can provide multi-field data to clarify the interaction between pipeline and permafrost degradation under different geological conditions, and guide the design and maintenance of the buried warm pipeline in permafrost regions.
2019055813 Angelopoulos, Michael (Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Potsdam, Germany); Westermann, Sebastian; Overduin, Paul; Faguet, Alexey; Olenchenko, Vladimir; Grosse, Guido and Grigoriev, Mikhail N. Heat and salt flow in subsea permafrost modeled with CryoGRID2: Journal of Geophysical Research: Earth Surface, 124(4), p. 920-937, illus. incl. 2 tables, sketch maps, 62 ref., April 2019.
Thawing of subsea permafrost can impact offshore infrastructure, affect coastal erosion, and release permafrost organic matter. Thawing is usually modeled as the result of heat transfer, although salt diffusion may play an important role in marine settings. To better quantify nearshore subsea permafrost thawing, we applied the CryoGRID2 heat diffusion model and coupled it to a salt diffusion model. We simulated coastline retreat and subsea permafrost evolution as it develops through successive stages of a thawing sequence at the Bykovsky Peninsula, Siberia. Sensitivity analyses for seawater salinity were performed to compare the results for the Bykovsky Peninsula with those of typical Arctic seawater. For the Bykovsky Peninsula, the modeled ice-bearing permafrost table (IBPT) for ice-rich sand and an erosion rate of 0.25 m/year was 16.7 m below the seabed 350 m offshore. The model outputs were compared to the IBPT depth estimated from coastline retreat and electrical resistivity surveys perpendicular to and crossing the shoreline of the Bykovsky Peninsula. The interpreted geoelectric data suggest that the IBPT dipped to 15-20 m below the seabed at 350 m offshore. Both results suggest that cold saline water forms beneath grounded ice and floating sea ice in shallow water, causing cryotic benthic temperatures. The freezing point depression produced by salt diffusion can delay or prevent ice formation in the sediment and enhance the IBPT degradation rate. Therefore, salt diffusion may facilitate the release of greenhouse gasses to the atmosphere and considerably affect the design of offshore and coastal infrastructure in subsea permafrost areas. Abstract Copyright (2019), The Authors.
2019055745 Zhao Wenwei (Nantong University, School of Geographic Science, Nantong, China); Andreev, Andrei A.; Tarasov, Pavel E.; Wennrich, Volker and Melles, Martin. Vegetation and climate during the penultimate interglacial of the northeastern Russian Arctic; the Lake El'gygytgyn pollen record: in Northern Eurasian lakes; late Quaternary glaciation and climate history (Melles, Martin, editor; et al.), Boreas, 48(2), p. 507-515, illus. incl. 2 tables, sketch map, 43 ref., April 2019.
We present a high-resolution reconstruction of the vegetation and climate dynamics during the penultimate interglacial, corresponding with Marine Isotope Stage (MIS) 7, based on detailed palynological analyses of lacustrine sediments from Lake El'gygytgyn, northeastern Siberia. The analysed sediments were deposited between 246 and 181 ka ago (late MIS 8 to early MIS 6.6). The interglacial vegetation was characterized by herb and shrub (mainly alder and birch) dominated plant communities. Pollen-based biome reconstruction shows a dominance of the tundra (TUND) biome, thus indicating rather open vegetation. Warmer intervals (MIS 7.5, 7.3 and 7.1) were marked by an increase in the cold deciduous forest (CLDE) biome scores and a synchronous decrease in the cold steppe (STEP) biome scores. The thermal maximum occurred during MIS 7.1, as indicated by the highest CLDE biome scores occurring in this period, and lasted ~10 ka, possibly favoured by the high precession-related summer insolation and the legacy of the preceding mild and dry stadial (MIS 7.2). In contrast, MIS 7.3 and 7.5 were characterized by shorter durations (~4 ka) and lower summer temperatures. The preceding cold glacial and stadial (MIS 8 and 7.4, respectively) might have led to an extensive distribution of permafrost that hindered vegetation development during the subsequent warm intervals. MIS 7.4 and 6.6 were cold and wet, probably triggered by low obliquity values and coevally low precession-related summer insolation. As a result, these periods were marked by significantly reduced summer temperatures and an enhanced snow-ice albedo feedback. The obtained reconstructions provide potential scenarios for future climate changes and allow a better understanding of the relationship between vegetation, climate and external/internal forcings in the high latitudes. Abstract Copyright (2019), John Wiley & Sons, Ltd.
2019061602 Ghias, Masoumeh Shojae (Université Laval, Department of Geology and Geological Engineering, Quebec City, QC, Canada); Therrien, René; Molson, John and Lemieux, Jean-Michel. Numerical simulations of shallow groundwater flow and heat transport in continuous permafrost setting under impact of climate warming: Canadian Geotechnical Journal = Revue Canadienne de Géotechnique, 56(3), p. 436-448, illus. incl. 3 tables, 34 ref., March 2019.
Numerical simulations of coupled groundwater flow and heat transport are used to address how hydrogeological conditions can affect permafrost dynamics. The simulations are based on a two-dimensional vertical-plane conceptual model of a study site at the Iqaluit Airport, Nunavut, Canada, which includes a 50 m deep permafrost terrain with a shallow active layer, overlain by a paved taxiway with winter snow-covered embankments. Coupled groundwater flow and advective-conductive heat transport with freeze-thaw dynamics, temperature-dependent pore-water freezing functions, and latent heat are included in the model. The simulation results show that a smooth (low-slope) freezing function with a higher residual unfrozen moisture content produced a deeper thaw front compared to that using a steeper freezing function, generating a maximum increase in the depth to permafrost of 17.5 m after 268 years. Permafrost thaw rates in high-permeability zones within a heterogeneous system were also relatively higher compared to an otherwise equivalent homogeneous soil, resulting in a maximum increase of 2.6 m in the depth to permafrost after 238 years. As recharge water cools while flowing along the upgradient permafrost table, advectively driven heat transport is paradoxically shown to temporarily increase the height of the permafrost table in downgradient areas.
2019052447 Overeem, Irina (University of Colorado at Boulder, Institute of Arctic and Alpine Research, Boulder, CO); Jafarov, Elchin; Wang Kang; Schaefer, Kevin; Stewart, Scott; Clow, Gary; Piper, Mark and Elshorbany, Yasin. Modeling the melting permafrost: Eos (Washington, DC), 100(3), p. 30-34, illus., 10 ref., March 2019.
2019054078 Lininger, Katherine B. (Colorado State University, Department of Geosciences, Fort Collins, CO); Wohl, E.; Rose, J. R. and Leisz, S. J. Significant floodplain soil organic carbon storage along a large high-latitude river and its tributaries: Geophysical Research Letters, 46(4), p. 2121-2129, illus., 60 ref., February 28, 2019.
High-latitude permafrost regions store large stocks of soil organic carbon (OC), which are vulnerable to climate warming. Estimates of subsurface carbon stocks do not take into account floodplains as unique landscape units that mediate and influence the delivery of materials into river networks. We estimate floodplain soil OC stocks within the active layer (seasonally thawed layer) and to a maximum depth of 1 m from a large field data set in the Yukon Flats region of interior Alaska. We compare our estimated stocks to a previously published data set and find that the OC stock estimate using our field data could be as much as 68% higher than the published data set. Radiocarbon measurements indicate that sediment and associated OC can be stored for thousands of years before erosion and transport. Our results indicate the importance of floodplains as areas of underestimated carbon storage, particularly because climate change may modify geomorphic processes in permafrost regions. Abstract Copyright (2019), . American Geophysical Union. All Rights Reserved.
2019058902 Yang Yuzhong (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, State Key Laboratory of Frozen Soil Engineering, Lanzhou, China); Wu Qingbai; Jin Huijun; Wang Qingfeng; Huang Yadong; Luo Dongliang; Gao Shuhui and Jin Xiaoying. Delineating the hydrological processes and hydraulic connectivities under permafrost degradation on northeastern Qinghai-Tibet Plateau, China: Journal of Hydrology, 569, p. 359-372, illus. incl. 5 tables, geol. sketch maps, 59 ref., February 2019.
Climatic warming has resulted in permafrost degradation and it is expected to alter the hydrological processes and hydraulic connectivity on the Qinghai-Tibet Plateau (QTP). Some important and pending issues for understanding the hydrological processes in permafrost regions are how much melting water from thawing permafrost can feed the stream water and how the hydraulic connectivities will be altered under continual permafrost degradation. In this study, the Source Area of the Yellow River locating on the Northeast QTP was studied by using stable isotopic method and field hydrological observation. Results exhibited significant seasonal hydrological variations of stream water, thermokarst lakes, and ground ice. Hydrograph separation suggested that precipitation is the main contributor to stream water in ice-free months, accounting for 53.5% and 52.2% of the streams on average for the two branches, respectively. The second source is springs, which contributed about 29.8% and 17.9%. However, the recharge from melting ice is also important; it exported an average of 16.7% and 13.2% to the surface stream. Conceptual model and stable isotopes emphasized the remarkable hydraulic connectivities between the precipitation, stream water, thermokarst lakes, spring, and the near-surface ground ice. Current findings provide a basic understanding of the log-term hydrological processes under permafrost degradation, and can offer an efficient way to assess future hydrological changes and water resource protection.
2019054268 Filbee-Dexter, Karen (Norwegian Institute for Water Research, Oslo, Norway); Wernberg, Thomas; Fredriksen, Stein; Norderhaug, Kjell Magnus and Pedersen, Morten Foldager. Arctic kelp forests; diversity, resilience and future: Global and Planetary Change, 172, p. 1-14, illus. incl. 1 table, sketch map, 162 ref., January 2019.
The Arctic is one of the most rapidly changing places on Earth and it is a sentinel region for understanding the range and magnitude of planetary changes, and their impacts on ecosystems. However, our understanding of arctic coastal ecosystems remains limited, and the impacts of ongoing and future climate change on them are largely unexplored. Kelp forests are the dominant habitat along many rocky Arctic coastlines, providing structure and food for economically and ecologically important species. Here we synthesize existing information on the distribution and diversity of arctic kelp forests and assess how ongoing changes in environmental conditions could impact the extent, productivity, and resilience of these important ecosystems. We identify regions where the range and growth of arctic kelp are likely to undergo rapid short-term increase due to reduced sea ice cover, increased light, and warming. However, we also describe areas where kelps could be negatively impacted by rising freshwater input and coastal erosion due to receding sea ice and melting permafrost. In some regions, arctic kelp forests have undergone sudden regime shifts due to altered ecological interactions or changing environmental conditions. Key knowledge gaps for arctic kelp forests include measures of extent and diversity of kelp communities (especially northern Canada and northeastern Russia), the faunal communities supported by many of these habitats, and the role of arctic kelp forests in structuring nearby pelagic and benthic food webs. Filling in these gaps and strategically prioritizing research in areas of rapid environmental change will enable more effective management of these important habitats, and better predictions of future changes in the coastal ecosystems they support and the services that they provide.
2019055551 Prud'homme, Charlotte (Université Paris I Panthéon-Sorbonne, Laboratoire de Géographie Physique, Environnements Quaternaires et Actuels, Meudon, France); Moine, Olivier; Mathieu, Jerome; Saulnier-Copard, Segolene and Antoine, Pierre. High-resolution quantification of earthworm calcite granules from Western European loess sequences reveals stadial-interstadial climatic variability during the last glacial: Boreas, 48(1), p. 257-268, illus. incl. strat. cols., geol. sketch map, 73 ref., January 2019.
High concentrations of calcite fossil granules produced by earthworms (ECG) have been identified in most of the stratigraphical units along the loess-palaeosol reference sequence of Nussloch (Germany). They are particularly abundant in interstadial brown soils and in tundra gley horizons, the latter reflecting short-term phases of aggradation then degradation of permafrost. These granules are characterized by a radial crystalline structure produced in the earthworms by specific bio-mineralization processes. In our study, we used this biological indicator combined with 14C and OSL dating, and sedimentological parameters to characterize millennial-time scale climatic variations recorded in loess sequences. The approach is based on high-resolution counts of ECG throughout a 17-m-thick loess sequence (332 samples). Strong increases in granule and mollusc concentrations suggest warmer climate conditions during palaeosol formation phases, associated with increasing biodiversity, biological activity and vegetation cover. Decreased granule concentrations occur within primary loess deposits, indicating a strong correlation with palaeoenvironmental conditions and demonstrating the reliability of ECG concentration variations as a new palaeoenvironmental proxy. Finally, this pattern is also recorded in loess sequences located about 600 km westward in northern France demonstrating the large-scale validity of this new palaeoclimatic proxy. Abstract Copyright (2019), John Wiley & Sons, Ltd.
2019054292 Ruebsam, Wolfgang (University of Kiel, Department of Organic and Isotope Geochemistry, Kiel, Germany); Mayer, Bernhard and Schwark, Lorenz. Cryosphere carbon dynamics control early Toarcian global warming and sea level evolution: Global and Planetary Change, 172, p. 440-453, illus. incl. geol. sketch map, 110 ref., January 2019.
The Earth's cryosphere represents a huge climate-sensitive carbon reservoir capable of releasing carbon dioxide (CO2) and methane (CH4) from permafrost soils or gas reservoirs capped by permafrost and ice caps upon rising global temperatures. Carbon release from these reservoirs has the potential to further accelerate global warming. Present day cryosphere demise is a focus of scientific research. The potential role of cryosphere carbon reservoirs in Mesozoic climate perturbations is even lesser known and currently underinvestigated. In contrast to previous views of a constantly warm Early Jurassic period, virtually lacking a cryosphere, recent studies have identified icehouse conditions for this time interval. Following these icehouse conditions, global warming occurred during the early Toarcian (~183 Ma) and was accompanied by a major carbon cycle anomaly as manifested in recurring negative carbon isotope excursions (CIEs). We propose that an initially volcanic-driven gentle rise of atmospheric temperature in the Early Toarcian triggered a melt-down of Earth's cryosphere which during the preceding Pliensbachian had expanded to the mid-latitudes and thus was highly vulnerable to warming. The rapid release of greenhouse gases, mainly as 13C-depleted CH4, or its oxidation product CO2, is recorded in the carbon isotope ratios of sedimentary organic matter and carbonates. Toarcian sediments display a series of orbitally-forced negative CIEs characterized by a frequency shift from eccentricity to obliquity cycles comparable to Pleistocene climate rhythms. This pattern is explained by a self-sustaining destabilization of labile cryosphere carbon reservoirs which started at mid-latitudes where eccentricity is most effective and then rhythmically progressed poleward to latitudes where obliquity dominates. The hitherto underestimated presence of a temperature-sensitive Pliensbachian cryosphere constituted an essential precondition for the early Toarcian climate change and its associated sea-level rise. The Pliensbachian cooling had transferred water into the terrestrial cryosphere causing a severe sea-level fall. Transgressive pulses at the Pliensbachian-Toarcian boundary and in the early Toarcian occurred concomitant to rising global temperatures and resulted from the meltdown of continental ice caps. This ice-volume effect and the massive discharge of freshwater into the oceans is well preserved in the exceptionally low d18O values of carbonates formed during the cryosphere demise and sea-level increase. Carbon and oxygen isotope ratios, climate and sea-level shifts thus underpin the presence of an Early Jurassic cryosphere and thereby highlight the role of glacio-eustatic mechanisms as main drivers of late Pliensbachian to early Toarcian geodynamics.
2019055546 Zawiska, Izabela (Polish Academy of Sciences, Department of Geoecology and Climatology, Warsaw, Poland); Apolinarska, Karina and Woszczyk, Michal. Holocene climate vs. catchment forcing on a shallow, eutrophic lake in eastern Poland: Boreas, 48(1), p. 166-178, illus. incl. 2 tables, sketch map, 72 ref., January 2019.
This paper presents a sedimentary record from Lake Lukie located in the southeastern part of the Central European Plain, beyond the reach of the maximum extent of the last glaciation. The lake has thermokarstic origin and developed during the last glacial termination due to subsidence of the sub-Quaternary carbonate basement triggered by permafrost thawing. A sediment core was investigated to reconstruct water trophic state and lake depth changes during the Holocene. We aimed at showing the relationship between ecological and geochemical changes in the lake and regional/supraregional climatic and hydrological trends throughout the Holocene. Results of subfossil Cladocera analysis were combined with data on the geochemistry and stable C and O isotopes in sedimentary carbonates. Isotopic and geochemical proxies helped to detect sources of sedimentary particles in the lake and thus to reconstruct changes in the intensity of atmospheric and catchment processes (e.g. precipitation and surface runoff). The Cladocera analysis results indicated endogenic processes in the lake such as trophic changes. Our data revealed that Lake Lukie has always been a rather eutrophic water body and the periods of particularly high productivity were in the lower Preboreal and upper Subatlantic. Periods of increased water depth were recorded in the lower Preboreal, lower Boreal and upper Subboreal, whereas low water stands were obtained during the late Preboreal, late Boreal, late Atlantic and Atlantic/Subboreal transition as well as during the lower Subboreal. The sediment succession from Lake Lukie provides the first full Holocene record of carbon and oxygen stable isotopes in lacustrine carbonates from the eastern part of the Central European Lowland. The record is characterized by uncommonly high d13C and d18O values of the carbonates resulting from a combination of within-lake processes and dissolution of the carbonate bedrock of Cretaceous age. The impact of the old carbonates on isotope values was helpful in the reconstruction of the catchment forcing on the lake. Abstract Copyright (2019), John Wiley & Sons, Ltd.
2019062190 Kramshoj, Magnus (University of Copenhagen, Center for Permafrost, Copenhagen, Denmark); Albers, Christian N.; Svendsen, Sarah H.; Björkman, Mats P.; Lindwall, Frida; Björk, Robert G. and Rinnan, Riikka. Volatile emissions from thawing permafrost soils are influenced by meltwater drainage conditions: Global Change Biology, 25(5), p. 1704-1716, illus. incl. 2 tables, 57 ref., 2019.
Vast amounts of carbon are bound in both active layer and permafrost soils in the Arctic. As a consequence of climate warming, the depth of the active layer is increasing in size and permafrost soils are thawing. We hypothesize that pulses of biogenic volatile organic compounds are released from the near-surface active layer during spring, and during late summer season from thawing permafrost, while the subsequent biogeochemical processes occurring in thawed soils also lead to emissions. Biogenic volatile organic compounds are reactive gases that have both negative and positive climate forcing impacts when introduced to the Arctic atmosphere, and the knowledge of their emission magnitude and pattern is necessary to construct reliable climate models. However, it is unclear how different ecosystems and environmental factors such as drainage conditions upon permafrost thaw affect the emission and compound composition. Here we show that incubations of frozen B horizon of the active layer and permafrost soils collected from a High Arctic heath and fen release a range of biogenic volatile organic compounds upon thaw and during subsequent incubation experiments at temperatures of 10°C and 20°C. Meltwater drainage in the fen soils increased emission rates nine times, while having no effect in the drier heath soils. Emissions generally increased with temperature, and emission profiles for the fen soils were dominated by benzenoids and alkanes, while benzenoids, ketones, and alcohols dominated in heath soils. Our results emphasize that future changes affecting the drainage conditions of the Arctic tundra will have a large influence on volatile emissions from thawing permafrost soils - particularly in wetland/fen areas.
2019062192 Voigt, Carolina (University of Montreal, Geography Department, Montreal, PQ, Canada); Marushchak, Maija E.; Mastepanov, Mikhail; Lamprecht, Richard E.; Christensen, Torben R.; Dorodnikov, Maxim; Jackowicz-Korczynski, Marcin; Lindgren, Amelie; Lohila, Annalea; Nykanen, Hannu; Oinonen, Markku; Oksanen, Timo; Palonen, Vesa; Treat, Claire C.; Martikainen, Pertti J. and Biasi, Christina. Ecosystem carbon response of an arctic peatland to simulated permafrost thaw: Global Change Biology, 25(5), p. 1746-1764, illus., 135 ref., 2019.
Permafrost peatlands are biogeochemical hot spots in the Arctic as they store vast amounts of carbon. Permafrost thaw could release part of these long-term immobile carbon stocks as the greenhouse gases (GHGs) carbon dioxide (CO2) and methane (CH4) to the atmosphere, but how much, at which time-span and as which gaseous carbon species is still highly uncertain. Here we assess the effect of permafrost thaw on GHG dynamics under different moisture and vegetation scenarios in a permafrost peatland. A novel experimental approach using intact plant-soil systems (mesocosms) allowed us to simulate permafrost thaw under near-natural conditions. We monitored GHG flux dynamics via high-resolution flow-through gas measurements, combined with detailed monitoring of soil GHG concentration dynamics, yielding insights into GHG production and consumption potential of individual soil layers. Thawing the upper 10-15 cm of permafrost under dry conditions increased CO2 emissions to the atmosphere (without vegetation: 0.74 ± 0.49 vs. 0.84 ± 0.60 g CO2-C m-2 day-1; with vegetation: 1.20 ± 0.50 vs. 1.32 ± 0.60 g CO2-C m-2 day-1, mean ± SD, pre- and post-thaw, respectively). Radiocarbon dating (14C) of respired CO2, supported by an independent curve-fitting approach, showed a clear contribution (9%-27%) of old carbon to this enhanced post-thaw CO2 flux. Elevated concentrations of CO2, CH4, and dissolved organic carbon at depth indicated not just pulse emissions during the thawing process, but sustained decomposition and GHG production from thawed permafrost. Oxidation of CH4 in the peat column, however, prevented CH4 release to the atmosphere. Importantly, we show here that, under dry conditions, peatlands strengthen the permafrost-carbon feedback by adding to the atmospheric CO2 burden post-thaw. However, as long as the water table remains low, our results reveal a strong CH4 sink capacity in these types of Arctic ecosystems pre- and post-thaw, with the potential to compensate part of the permafrost CO2 losses over longer timescales.
2019057811 Drewes, Julia (University of Potsdam, Institute of Earth and Environmental Science, Potsdam, Germany); Moreiras, Stella and Korup, Oliver. Permafrost activity and atmospheric warming in the Argentinian Andes: Geomorphology, 323, p. 13-24, illus. incl. 5 tables, sketch maps, 65 ref., December 15, 2018.
Rock glaciers are permafrost or glacial landforms of debris and ice that deform under the influence of gravity. Recent estimates hold that, in the semiarid Chilean Andes for example, active rock glaciers store more water than glaciers. However, little is known about how many rock glaciers might decay because of global warming and how much this decay might contribute to water and sediment release. We investigated an inventory of >6500 rock glaciers in the Argentinian Andes, spanning the climatic gradient from the Desert Andes to cold-temperate Tierra del Fuego. We used active rock glaciers as a diagnostic of permafrost, assuming that the toes mark the 0°C isotherm in climate scenarios for the twenty-first century and their impact on freezing conditions near the rock glacier toes. We find that, under future worst case warming, up to 95% of rock glaciers in the southern Desert Andes and in the Central Andes will rest in areas above 0°C and that this freezing level might move up more than twice as much (~500 m) as during the entire Holocene (~200 m). Many active rock glaciers are already well below the current freezing level and exemplify how local controls may confound regional prognoses. A Bayesian Multifactor Analysis of Variance further shows that only in the Central Andes are the toes of active rock glaciers credibly higher than those of inactive ones. Elsewhere in the Andes, active and inactive rock glaciers occupy indistinguishable elevation bands, regardless of aspect, the formation mechanism, or shape of rock glaciers. The state of rock glacier activity predicts differences in elevations of toes to 140 m at best so that regional inference of the distribution of discontinuous permafrost from rock-glacier toes cannot be more accurate than this in the Argentinian Andes. We conclude that the Central Andes-where rock glaciers are largest, cover the most area, and have a greater density than glaciers-is likely to experience the most widespread disturbance to the thermal regime of the twenty-first century.
2019061438 Du Zengfeng (Chinese Academy of Sciences, Institute of Oceanology, Qingdao, China); Zhang Xin; Xi Shichuan; Li Lianfu; Luan Zhendong; Lian Chao; Wang Bing and Yan Jun. In situ Raman spectroscopy study of synthetic gas hydrate formed by cold seep flow in the South China Sea: in South China Sea seep (Feng Dong, editor; et al.), Journal of Asian Earth Sciences, 168, p. 197-206, illus. incl. 1 table, sketch map, 65 ref., December 2018. Includes appendices.
Properties of gas hydrate are commonly investigated in laboratory by simulators or studied using the hydrate samples recovered from permafrost and marine sediments. Here synthetic gas hydrate (SGH) is quickly formed for the first time by fluids and bubbles erupted from the active cold seeps at the Formosa Ridge in the South China Sea (SCS). SGH samples are in situ detected by a Raman insertion probe for gas hydrate (RiP-Gh) which is deployed by the remotely operated vehicle (ROV) Faxian. Both spatial and temporal in situ Raman spectra of the SGH samples are acquired in order to determine the structure and the evolution of the synthetic gas hydrate. Authigenic carbonate debris or other debris serving as nucleation particles, which is found in the in situ Raman spectra of SGH samples for the first time, may be one factor that can promote the formation of synthetic gas hydrate. The gas-water interface demonstrated by the observation results, also contributes to the quick formation of SGH samples, which agrees well with the previous study. In situ Raman spectra of three SGH samples which have been placed on the seafloor for 0 h, 4 h and 21 h respectively are acquired. Laboratory Raman spectra of one sample which has been surprisingly found and recovered after 9840 h (410 days) since formed on the seafloor are also acquired. The Raman spectra of the four SGH samples indicate that the methane large-to-small cage occupancy ratios of the hydrates vary from 1.01 to 1.39, and the ratios of methane large-to-gas of the hydrates increase from 0.53 to 1.55. Overall, our work suggests a new explanation for the quick formation of gas hydrate compared to that in laboratory simulation work, and reveals the evolution of synthetic gas hydrate after quick formation, which provides a new insight for the study of natural gas hydrate.
2019053969 Gilbert, Graham L. (University Centre in Svalbard, Department of Arctic Geology, Longyearbyen, Norway); O'Neill, Hugh B.; Nemec, Wojciech; Thiel, Christine; Christiansen, Hanne H. and Buylaert, Jan-Pieter. Late Quaternary sedimentation and permafrost development in a Svalbard fjord-valley, Norwegian high Arctic: Sedimentology, 65(7), p. 2531-2558, illus. incl. sects., 4 tables, sketch map, 115 ref., December 2018.
The infilling history of the Adventdalen fjord-valley in central Spitsbergen is reconstructed, with a focus on permafrost development, based on sedimentological and cryostratigraphic evidence from drilling cores. The techniques of optically stimulated luminescence and radiocarbon accelerator mass-spectrometry dating were used to establish sediment chronology. The fjord-fill sedimentary succession includes the fjord-bottom late Weichselian subglacial till of the Last Glacial Maximum, the early Holocene muddy glaciomarine deposits with ice-rafted debris formed during the fjord deglaciation, and the younger Holocene deposits of a fjord-head Gilbert-type delta of which the fluvial distributary plain shows raised alluvial terraces hosting aeolian sedimentation. This sedimentary record of the last glaciation/deglaciation cycle is interpreted in terms of sequence stratigraphy. Zones of epigenetic and syngenetic permafrost are recognized from the vertical distribution of cryofacies, with a conclusion that the formation of permafrost commenced and extended down-fjord as the fluvio-deltaic fjord-fill was gradually reaching subaerial exposure. The upwards-grown syngenetic permafrost and the top part of downwards-grown epigenetic permafrost below contain excess ice in a suite of cryofacies indicating ground-ice segregation and segregative intrusion. The deeper epigenetic permafrost is ice-poor and contains cryofacies formed solely by segregation processes. This case study may serve as an analogue for other similar Arctic fjord-valleys where the fjord-head shoreline was established during the post-Weichselian deglaciation. Abstract Copyright (2018), International Association of Sedimentologists.
2019057816 Levy, Joseph S. (Colgate University, Department of Geology, Hamilton, NY); Fountain, Andrew G.; Obryk, Maciej K.; Telling, Jennifer; Glennie, Craig L.; Pettersson, Richard; Gooseff, Michael N. and Van Horn, David J. Decadal topographic change in the McMurdo dry valleys of Antarctica; thermokarst subsidence, glacier thinning, and transfer of water storage from the cryosphere to the hydrosphere: Geomorphology, 323, p. 80-97, illus. incl. 1 table, sketch maps, 96 ref., December 15, 2018.
Recent local-scale observations of glaciers, streams, and soil surfaces in the McMurdo Dry Valleys of Antarctica (MDV) have documented evidence for rapid ice loss, glacial thinning, and ground surface subsidence associated with melting of ground ice. To evaluate the extent, magnitude, and location of decadal-scale landscape change in the MDV, we collected airborne lidar elevation data in 2014-2015 and compared these data to a 2001-2002 airborne lidar campaign. This regional assessment of elevation change spans the recent acceleration of warming and melting observed by long-term meteorological and ecosystem response experiments, allowing us to assess the response of MDV surfaces to warming and potential thawing feedbacks. We find that locations of thermokarst subsidence are strongly associated with the presence of excess ground ice and with proximity to surface or shallow subsurface (active layer) water. Subsidence occurs across soil types and landforms, in low-lying, low-slope areas with impeded drainage and also high on steep valley walls. Glacier thinning is widespread and is associated with the growth of fine-scale roughness. Pond levels are rising in most closed-basin lakes in the MDV, across all microclimate zones. These observations highlight the continued importance of insolation-driven melting in the MDV. The regional melt pattern is consistent with an overall transition of water storage from the local cryosphere (glaciers, permafrost) to the hydrosphere (closed basin lakes and ponds as well as the Ross Sea). We interpret this regional melting pattern to reflect a transition to Arctic and alpine-style, hydrologically mediated permafrost and glacial melt.
2019052396 von Deimling, Thomas Schneider (Max Planck Institute for Meteorology, Hamburg, Germany); Kleinen, Thomas; Hugelius, Gustaf; Knoblauch, Christian; Beer, Christian and Brovkin, Victor. Long-term deglacial permafrost carbon dynamics in MPI-ESM: Climate of the Past, 14(12), p. 2011-2036, illus. incl. 2 tables, 74 ref., December 2018.
We have developed a new module to calculate soil organic carbon (SOC) accumulation in perennially frozen ground in the land surface model JSBACH. Running this offline version of MPI-ESM we have modelled long-term permafrost carbon accumulation and release from the Last Glacial Maximum (LGM) to the pre-industrial (PI) age. Our simulated near-surface PI permafrost extent of 16.9 ´ 106 km2 is close to observational estimates. Glacial boundary conditions, especially ice sheet coverage, result in profoundly different spatial patterns of glacial permafrost extent. Deglacial warming leads to large-scale changes in soil temperatures, manifested in permafrost disappearance in southerly regions, and permafrost aggregation in formerly glaciated grid cells. In contrast to the large spatial shift in simulated permafrost occurrence, we infer an only moderate increase in total LGM permafrost area (18.3 ´ 106 km2) - together with pronounced changes in the depth of seasonal thaw. Earlier empirical reconstructions suggest a larger spread of permafrost towards more southerly regions under glacial conditions, but with a highly uncertain extent of non-continuous permafrost. Compared to a control simulation without describing the transport of SOC into perennially frozen ground, the implementation of our newly developed module for simulating permafrost SOC accumulation leads to a doubling of simulated LGM permafrost SOC storage (amounting to a total of ~ 150 PgC). Despite LGM temperatures favouring a larger permafrost extent, simulated cold glacial temperatures - together with low precipitation and low CO2 levels - limit vegetation productivity and therefore prevent a larger glacial SOC build-up in our model. Changes in physical and biogeochemical boundary conditions during deglacial warming lead to an increase in mineral SOC storage towards the Holocene (168 PgC at PI), which is below observational estimates (575 PgC in continuous and discontinuous permafrost). Additional model experiments clarified the sensitivity of simulated SOC storage to model parameters, affecting long-term soil carbon respiration rates and simulated ALDs. Rather than a steady increase in carbon release from the LGM to PI as a consequence of deglacial permafrost degradation, our results suggest alternating phases of soil carbon accumulation and loss as an effect of dynamic changes in permafrost extent, ALDs, soil litter input, and heterotrophic respiration.
2019055595 Ward, Melissa K. (McGill University, Department of Geography, Montreal, QC, Canada) and Pollard, Wayne H. A hydrohalite spring deposit in the Canadian High Arctic; a potential Mars analogue: Earth and Planetary Science Letters, 504, p. 126-138, illus. incl. 1 table, sketch map, 46 ref., December 15, 2018.
On Axel Heiberg Island in the Canadian High Arctic, low temperature perennial saline springs occur despite thick permafrost and cold polar desert conditions marked by a mean annual air temperature close to -20°C. We present the first comprehensive geomorphic study of the Stolz Diapir Spring (79°04'30"N; 87°04'30"W), a unique groundwater system due to its known fresh water source and sodium chloride-dominated chemistry. During winter, spring discharge precipitates hydrohalite (NaCl·2H2O) by freezing fractionation that forms a pool and barrage system morphologically similar to carbonate travertines and tufas found in temperate climates. The deposit is the largest hydrohalite accumulation on Earth based on published sources. This system experiences dramatic seasonal differences in hydrology and mineralogy marked by a switch from winter regime of salt deposition and cascading surface flow from pool to pool to a summer regime marked by chemical and mechanical erosion and deposit subsurface flow. The warmer temperatures also cause the decomposition of hydrohalite to halite. Accordingly, this site is a useful analogue for similar structures identified on Mars located in areas rich in evaporite minerals and lacking evidence of volcanic activity.
2019057777 Gwiazda, Roberto (Monterey Bay Aquarium Research Institute, Moss Landing, CA); Paull, Charles K.; Dallimore, Scott R.; Melling, Humfrey; Jin, Young Keun; Hong, Jong Kuk; Riedel, Michael; Lundsten, Eve; Anderson, Krystle and Conway, K. Freshwater seepage into sediments of the shelf, shelf edge, and continental slope of the Canadian Beaufort Sea: Geochemistry, Geophysics, Geosystems - G3, 19(9), p. 3039-3055, illus. incl. sketch maps, 92 ref., September 2018.
Long-term warming of the continental shelf of the Canadian Beaufort Sea caused by the transgression associated with the last deglaciation may be causing decomposition of relict offshore subsea permafrost and gas hydrates. To evaluate this possibility, pore waters from 118 sediment cores up to 7.3-m long were taken on the shelf and slope and analyzed for chloride concentrations and d180 and dD composition. We observed downcore decreases in pore waters Cl- concentration in sediments from all sites from the inner shelf (<20-m water depth), from the shelf edge, from the outer slope (down to 1,000-m water depths), and from localized shelf features such as midshelf pingo-like features and inner shelf pockmarks. In contrast, pore water freshening is absent from all investigated cores of the Mackenzie Trough. Downcore pore waters Cl- concentration decreases indicate regional widespread freshwater seepage. Extrapolations to zero Cl- of pore water Cl- versus d180 regression lines indicate that freshwaters in these environments carry different isotope signatures and thus are sourced from different reservoirs. These isotopic signatures indicate that freshening of shelf sediments pore waters is a result of downward infiltration of Mackenzie River water, freshening of shelf edge sediments is due to relict submarine permafrost degradation or gas hydrate decomposition under the shelf, and freshening of slope sediments is consistent with regional groundwater flow and submarine groundwater discharge as far as 150 km from shore. These results confirm ongoing decomposition of offshore permafrost and suggest extensive current groundwater discharge far from the coast. Abstract Copyright (2018). The Authors.
2019058475 Markkula, Inkeri (University of Turku, Biodiversity Unit, Turku, Finland); Oksanen, Pirita and Kuhry, Peter. Indicator value of oribatid mites in determining past permafrost dynamics in northern European sub-Arctic peatlands: Boreas, 47(3), p. 884-896, illus. incl. strat. cols., 3 tables, sketch map, 79 ref., July 2018.
Permafrost dynamics play an important role in the surface hydrology and carbon balance of northern peatlands. Plant macrofossil analysis with radiocarbon dating has been widely used in detecting past permafrost dynamics in peatlands; however, there is a lack of permafrost-specific plant indicator species, which makes it challenging to determine the exact timing of historical permafrost aggradation. We investigated the indicator value of oribatid mites in determining past permafrost dynamics in sub-Arctic peatlands. Analyses of subfossil oribatid mite assemblages of Holocene peat profiles from two mires, one in northern Finland and one in northeastern European Russia, were carried out and interpreted using modern calibration data from the same study areas. The results were compared with previously published reconstructions of permafrost history based on plant macrofossil analyses from the same locations. The results suggest that the oribatid mites Carabodes labyrinthicus, Chamobates borealis and Neoribates aurantiacus are promising indicator species to detect past permafrost occurrence in peatlands. In addition, N. aurantiacus is clearly associated with the presence of lichens, which is particularly useful because lichen remains are rarely preserved in peat deposits. Results are in accordance with earlier studies showing that oribatid mites are useful indicators of past environmental change. Abstract Copyright (2018), John Wiley & Sons, Ltd.
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