15006895 Dou, Shan (University of California, Berkeley, Department of Earth and Planetary Science, Berkeley, CA) and Ajo-Franklin, Jonathan B. Full-wavefield inversion of surface waves for mapping embedded low-velocity zones in permafrost: Geophysics, 79(6), p. EN107-EN124, illus. incl. 4 tables, 79 ref., December 2014.
Surface waves are advantageous for mapping seismic structures of permafrost, in which irregular velocity gradients are common and thus the effectiveness of refraction methods are limited. Nevertheless, the complex velocity structures that are common in permafrost environments often yield unusual dispersion spectra, in which higher-order and leaky modes are dominant. Such unusual dispersion spectra were prevalent in the multichannel surface-wave data acquired from our permafrost study site at Barrow, Alaska. Owing to the difficulties in picking and identifying dispersion curves from these dispersion spectra, conventional surface-wave inversion methods become problematic to apply. To overcome these difficulties, we adopted a full-wavefield method to invert for velocity models that can best fit the dispersion spectra instead of the dispersion curves. The inferred velocity models were consistent with collocated electric resistivity results and with subsequent confirmation cores, which indicated the reliability of the recovered seismic structures. The results revealed embedded low-velocity zones underlying the ice-rich permafrost at our study site - an unexpected feature considering the low ground temperatures of -10°C to -8°C. The low velocities in these zones (~70%-80% lower than the overlying ice-rich permafrost) were most likely caused by saline pore-waters that prevent the ground from freezing, and the resultant velocity structures are vivid examples of complex subsurface properties in permafrost terrain. We determined that full-wavefield inversion of surface waves, although carrying higher computational costs than conventional methods, can be an effective tool for delineating the seismic structures of permafrost.
15009597 Abbott, Benjamin W. (University of Alaska, Fairbanks, Institute of Arctic Biology, Fairbanks, AK); Larouche, Julia R.; Jones, Jeremy B., Jr.; Bowden, William B. and Balser, Andrew W. Elevated dissolved organic carbon biodegradability from thawing and collapsing permafrost: Journal of Geophysical Research: Biogeosciences, 119(G10), p. 2049-2063, illus. incl. 4 tables, sketch map, 76 ref., October 2014.
As high latitudes warm, a portion of the large organic carbon pool stored in permafrost will become available for transport to aquatic ecosystems as dissolved organic carbon (DOC). If permafrost DOC is biodegradable, much will be mineralized to the atmosphere in freshwater systems before reaching the ocean, accelerating carbon transfer from permafrost to the atmosphere, whereas if recalcitrant, it will reach marine ecosystems where it may persist over long time periods. We measured biodegradable DOC (BDOC) in water flowing from collapsing permafrost (thermokarst) on the North Slope of Alaska and tested the role of DOC chemical composition and nutrient concentration in determining biodegradability. DOC from collapsing permafrost was some of the most biodegradable reported in natural systems. However, elevated BDOC only persisted during active permafrost degradation, with a return to predisturbance levels once thermokarst features stabilized. Biodegradability was correlated with background nutrient concentration, but nutrient addition did not increase overall BDOC, suggesting that chemical composition may be a more important control on DOC processing. Despite its high biodegradability, permafrost DOC showed evidence of substantial previous microbial processing, and we present four hypotheses explaining this incongruity. Because thermokarst features form preferentially on river banks and lake shores and can remain active for decades, thermokarst may be the dominant short-term mechanism delivering sediment, nutrients, and biodegradable organic matter to aquatic systems as the Arctic warms. Abstract Copyright (2014), . American Geophysical Union. All Rights Reserved.
15007610 Tremblay, Sylvain (Université Laval, Centre d'Études Nordiques, Quebec City, QC, Canada); Bhiry, Najat and Lavoie, Martin. Long-term dynamics of a palsa in the sporadic permafrost zone of northwestern Quebec (Canada): Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre, 51(5), p. 500-509 (French sum.), illus. incl. strat. col., 1 table, sketch map, 64 ref., May 2014.
In the sporadic permafrost zone of the James Bay region in northwestern Quebec (Canada), permafrost has been showing signs of advanced degradation for the past 50 years. Several palsa peatlands are among the few remaining sites with evidence of permafrost presence. We conducted a high-resolution stratigraphic macrofossil analysis of a palsa situated on the shore of Duncan Lake, near the southern limit of sporadic permafrost distribution, to reconstruct the stages of peatland development since its formation, examine the respective roles of allogenic and autogenic factors in this development, and determine the period during which permafrost and palsa formed. Organic matter began to accumulate following the retreat of the postglacial Tyrrell Sea. Three main stages can be identified in the peatland history at the sampling site: lake (>5310 cal years BP), minerotrophic peatland (5310-760 cal years BP), and ombrotrophic peatland (<760 cal years BP). This hydroseral succession reflects primarily an autogenic sequence. Permafrost and palsa formed sometime during the last 300 years, most likely around 1750 A.D. (200 cal years BP) in response to the cold climatic conditions of the Little Ice Age.
15009065 Rosset, Etienne (University of Fribourg, Department of Geosciences, Fribourg, Switzerland); Hilbich, Christin; Schneider, Sina and Hauck, Christian. Automatic filtering of ERT monitoring data in mountain permafrost: Near Surface Geophysics, 11(4), p. 423-433, 39 ref., 2013.
Continuous monitoring of Electrical Resistivity Tomography (ERT) surveys can be a powerful tool for all kind of long-term applications in the field of hydrogeophysics and cold-region geophysics due to its high sensitivity to changes in water and ice content of the near subsurface. However, the large amount of data often calls for autonomous data processing schemes. In this study, a new filter algorithm designed to automatically detect and delete measurement errors from multiple ERT monitoring data is presented. Three successive filter steps were developed in order to eliminate technical errors, overall high-value outliers and relative outliers within single data levels. The filter procedure is site-independent and was tested on four different mountain permafrost sites in the Swiss Alps, representing various landforms (talus slope, rock plateau, rock glacier, bedrock). The filter performance is assessed by analysing the effect of the filter procedure on the mean apparent resistivity and on the resulting data misfit of the inversion and both, after the entire filter procedure as well as after each individual filter step. The new filter procedure is expected to yield rapid and high-quality filtering for monitoring applications. In our study, the procedure is developed to support early detection of electrical resistivity changes associated with freezing and thawing events in permafrost conditions. The filter is applied to 128 ERT data sets from permafrost monitoring stations in Switzerland, including a four year long (2005-2008) ERT monitoring data set from the high-mountain permafrost monitoring station Stockhorn, which serves as an illustrating example.
15011586 Bataille, Clément P. (University of Utah, Department of Geology and Geophysics, Salt Lake City, UT); Brennan, Sean R.; Hartmann, Jens; Moosdorf, Nils; Wooller, Matthew J. and Bowen, Gabriel J. A geostatistical framework for predicting variations in strontium concentrations and isotope ratios in Alaskan rivers: Chemical Geology, 389, p. 1-15, illus. incl. 5 tables, sketch maps, 96 ref., December 11, 2014. Includes appendices.
Bataille and Bowen (2012) developed models to predict variations in the ratio of 87-strontium to 86-strontium (87Sr/86Sr) in rocks (bedrock model) and rivers (catchment water model) for regional provenance studies. Here, we revisit those models' formulation and calibration and apply them to predict Sr concentrations ([Sr]) and 87Sr/86Sr of Alaskan rivers. In a first step, we add several new components and/or improvements to resolve limitations of the model, including: 1) an independent siliciclastic sediment sub-model, 2) an explicit consideration of 87Sr/86Sr variability at the local scale, and 3) a fully-coupled assessment of prediction uncertainty. Tested against a compilation of 885 87Sr/86Sr rock analyses across Alaska, the new bedrock model significantly improves 87Sr/86Sr prediction accuracy in both igneous and sedimentary settings. In a second step, we develop a fully independent Sr chemical weathering model calibrated using a database of 339 [Sr] analyses from rivers of Northern Hemisphere high-latitude and predicting spatial variations in the rate of Sr release from rocks as a function of lithology, permafrost cover and slope. We combine the bedrock and Sr chemical weathering models to predict [Sr] and 87Sr/86Sr in Alaskan rivers. Tested on a dataset of 61 water samples, the resulting catchment water model explains 82% of 87Sr/86Sr variations in Alaskan rivers. We compare the average [Sr] and 87Sr/86Sr of Alaskan runoff estimated with the catchment water model to observed data of the Yukon River. The estimated average [Sr] and 87Sr/86Sr of Alaskan surface runoff - 104.3 mg/L and 0.7098 respectively - differ significantly from those of the Yukon River - 139.3 mg/L and 0.7137 respectively. This result calls into question the assumption that [Sr] and 87Sr/86Sr values estimated only from large rivers are representative of the Sr weathering flux from the entire Earth surface. The data products from this work provide an alternative basis for estimating 87Sr/86Sr values in rocks and rivers for regional provenance and chemical weathering studies across Alaska. Abstract Copyright (2014) Elsevier, B.V.
15007413 Gadek, Bogdan (University of Silesia, Department of Geomorphology, Sosnowiec, Poland). Climatic sensitivity of the non-glaciated mountains cryosphere (Tatra Mts., Poland and Slovakia): Global and Planetary Change, 121, p. 1-8, illus. incl. sketch map, 46 ref., October 2014.
This paper concerns the response of the conditioned by orography cryosphere of the non-glaciated mountains of mid-latitude to the climate impulses. It presents the relationships among the air temperature, precipitation, snow cover, lake ice cover, firn-ice patches (glacierets) and permafrost in the Tatras. The data from the warmest multi-year in the history of the local meteorological measurements and statistical models (multiple regression) have been used. The results indicate that all the components of the contemporary cryosphere are very sensitive to the changes in the air temperature in winter or snow precipitation/accumulation. Due to the diverse orographic conditions, interannual variability of seasonal and perennial, surface and subsurface ice deposits in the mountain areas may not be synchronous. However, the long-term trends of this variability reflect the changes in the global climate system. Abstract Copyright (2014) Elsevier, B.V.
15004145 Wang Jiaoyue (Chinese Academy of Sciences, Northeast Institute of Geography and Agroecology, Changchun, China); Song Changchun; Hou, Aixin; Miao Yuqing; Yang Guisheng and Zhang Jing. Effects of freezing-thawing cycle on peatland active organic carbon fractions and enzyme activities in the Da Xing'anling Mountains, northeast China: Environmental Earth Sciences, 72(6), p. 1853-1860, illus. incl. 3 tables, 42 ref., September 2014.
Freezing-thawing cycle (FTC) is an important environmental factor affecting soil physicochemical properties and microbial activities. The effects of FTC at mid-high latitudes, especially in the permafrost regions impacted by global warming, have become a hot topic for research. However, the responses of active organic carbon fractions and soil enzyme activities to FTC in the active layers of permafrost regions remain far from certain. In this study, soil samples from three soil layers of (0-15, 15-30 and 30-45 cm) an undisturbed peatlands in Da Xing'anling Mountains, Northeast China, were collected, and then subjected to various FTCs with a large (10 to -10 °C) and a small (5 to -5 °C) amplitudes, respectively. Results showed that the soil active organic carbon fractions and enzyme activities were sensitive to FTCs. The FTCs significantly increased water-extracted organic carbon (WEOC) concentration in the three soil layers by approximately 5-28 % for the large amplitude and 22-36 % for the small amplitude. In contrast, FTCs significantly decreased microbial biomass carbon (MBC) concentration, cellulase, amylase and invertase activities. Overall, the damage of FTCs to soil enzymes was severe at the deeper soil depths and for the large amplitude. Interestingly, the soil WEOC concentration was lower at the large amplitude of FTC compared with the small amplitude. When the numbers of FTCs increased, WEOC concentration began to decrease and MBC concentration and enzyme activities began to increase. In addition, the significant correlations between active organic carbon fractions and enzyme activities indicate that the increased WEOC by FTCs plays an important role in soil microbes and enzyme activities. Copyright 2014 Springer-Verlag Berlin Heidelberg
15007729 Arcone, Steven (U. S. Army Cold Regions Research and Engineering Laboratory, Engineer Research and Development Center, Hanover, NH); Campbell, Seth and Pfeffer, W. Tad. GPR profiles of glacial till and its transition to bedrock; interpretation of water content, depth and signal loss from diffractions: Journal of Environmental & Engineering Geophysics, 19(4), p. 207-228, illus. incl. geol. sketch maps, 54 ref., December 2014.
We discuss GPR reflection profiles that we recorded on glacial till and a colluvial diamict at several locations in New Hampshire, and from which we interpret water contents, depths and rates of signal loss. We used pulses centered from 150-200 MHz and 300-360 MHz. The boulder-rich sediments reside over granitic and metavolcanics, the horizons of which we recognize from the relative strengths and phase of their waveforms, underlying fractures, and well-developed diffraction asymptotes. The till produced an apparent dense distribution of diffractions with limited asymptotes and dispersion, and occasional minor stratification. We use these diffractions and moveout profiles to calculate relative dielectric permittivities between 17 and 27, values which suggest up to 30% volumetric water, and likely saturation within these over-consolidated sediments. The evidence for transitions from till to bedrock ranges from a simple horizon to complex horizon segments, all characterized by diffractions and amenable to single-layer migration. A gradational loss in diffraction strength with depth suggests gradational weathering or changes in grain size as the cause. Maximum profiled depths range from 4 m to at least 10 m, with estimated scattering attenuation rates of about 3.3 dB m-1. In contrast, one and possible two colluvial diamicts, which likely contained 3-m-size boulders, show short segments of stratification, rare diffraction asymptotes, allow more than 20-m penetration and provide scattering losses of about 0.5 dB m-1. We measured extremely low conductivity and calculated permittivities ranging from 9-12, which suggest high densities and volumetric water content of 4-12%. Low, single scattering loss and deep penetration in the till are consistent with evidence of ground waves traveling up to 40 m one way. The phase polarity of waveforms within till and colluvial events show they may originate from either high or low dielectric contrasts, likely related to water or large boulders, respectively.
15011300 Joyce, Steven (AMEC, Didcot, United Kingdom); Hartley, Lee; Applegate, David; Hoek, Jaap and Jackson, Peter. Multi-scale groundwater flow modeling during temperate climate conditions for the safety assessment of the proposed high-level nuclear waste repository site at Forsmark, Sweden: Hydrogeology Journal, 22(6), p. 1233-1249 (French, Spanish, Chinese, Portuguese sum.), illus. incl. 5 tables, geol. sketch maps, 77 ref., September 2014.
15004160 Li Ren (Chinese Academy of Sciences, Cryosphere Research Station on the Qinghai-Tibet Plateau, Laboratory of Cryospheric Sciences, Lanzhou, China); Zhao Lin; Wu Tonghua; Ding Yongjian; Xiao Yao; Hu Guojie; Zou Defu; Li Wangping; Yu Wenjun; Jiao Yongliang and Qin Yanhui. The impact of surface energy exchange on the thawing process of active layer over the northern Qinghai-Xizang Plateau, China: Environmental Earth Sciences, 72(6), p. 2091-2099, illus. incl. 4 tables, sketch map, 54 ref., September 2014.
In this study, we collected radiation and active layer temperature data observed in the northern Qinghai-Xizang Plateau during the period 2006-2008 in order to analyze the impact of surface energy balance on the thawing process of the active layer. Results show that surface energy exhibits an obvious seasonal variation. The largest values of energy variables including global radiation, net radiation, soil heat flux and surface heat source intensity occur during June and July, while the smallest values occur in November and December. The active layer is generally dominated by an endothermic process. During the freeze-thaw period, the variation process of the active layer temperature is similar to that of surface energy. The seasonal thawing depth is closely related to the process of surface energy exchange. During the thawing period, seasonal thawing depth gradually increases as more solar energy enters the surface. When the surface energy accumulation is 0.0 MJ m-2 d-1, the seasonal thawing depth is the smallest. The seasonal thawing depth gradually increases with further accumulation of surface energy. Thus, the variation processes between the surface energy and seasonal thawing depth can be expressed by a power relation. The values of seasonal thawing depth calculated with the empirical relationship provided in this study agree well with the observed values. The relative error between calculated and observed values is less than 12 %. These results show that this empirical relationship can be successfully used to describe the behavior of active layers. Copyright 2014 Springer-Verlag Berlin Heidelberg
15011299 Selroos, Jan-Olof (Swedish Nuclear Fuel and Waste Management Company (SKB), Stockholm, Sweden) and Follin, Sven. Overview of hydrogeological safety assessment modeling conducted for the proposed high-level nuclear waste repository site at Forsmark, Sweden: Hydrogeology Journal, 22(6), p. 1229-1232, 23 ref., September 2014.
15011301 Vidstrand, Patrik (TerraSolve, Floda, Sweden); Follin, Sven; Selroos, Jan-Olof and Naslund, Jens-Ove. Groundwater flow modeling of periods with periglacial and glacial climate conditions for the safety assessment of the proposed high-level nuclear waste repository site at Forsmark, Sweden: Hydrogeology Journal, 22(6), p. 1251-1267 (Spanish, French, Chinese, Portuguese sum.), illus. incl. geol. sketch maps, 66 ref., September 2014.
15003961 Kondo, Reisuke (Meiji University, School of Arts and Letters, Tokyo, Japan); Tsukamoto, Sumiko and Sakamoto, Tatsuhiko. Luminescence chronology of a fossil periglacial wedge and volcanic fan in Rishiri Island, northern Hokkaido, Japan: Daiyonki-Kenkyu = Quaternary Research, 53(2), p. 95-101, (Japanese) (English sum.), illus. incl. 1 table, 27 ref., April 2014.
15008989 Sprafke, Tobias; Terhorst, Birgit; Peticzka, Robert and Thiel, Christine. Paudorf locus typicus (Lower Austria) revisited; the potential of the classic loess outcrop for middle to late Pleistocene landscape reconstructions: in Middle to upper Pleistocene paleosols in Austria (Freund, Holger, editor; et al.), Eiszeitalter und Gegenwart - Quarternary Science Journal, 62(1), p. 59-72, 62 ref., 2013.
The more than 12 m thick loess-paleosol sequence in Paudorf, Lower Austria, has been known for decades as locus typicus of the "Paudorfer Bodenbildung" (Paudorf paleosol). The upper section of the outcrop contains an up to 1 m thick pedocomplex that developed during MIS 5. The differentiated sequence of loess-like sediment below, including a more than 2 m thick pedocomplex in its basal part, is an exceptional archive of landscape evolution from the Middle Pleistocene. Herein we present detailed paleopedological and sedimentological surveys, as well as first micromorphological observations to address the sequence in its entirety and the processes leading to its genesis. Furthermore, high resolution color and carbonate analyses, as well as detailed texture analyses, have resulted in a substantial database. The studies show that the loess sediments were subject to a polygenetic development under periglacial conditions reflected in eolian silt and fine sand accumulation, admixture of local material during (mostly solifluidal) redeposition and in situ processes. Horizons with signs of pedogenesis, particularly the two pedocomplexes, document longer phases of stability; the stages of development can be correlated to equivalent sequences and seen as paleoclimatic signals where chronological data are available. The upper pedocomplex is a Chernozem of the early last glacial (MIS 5c-[a?]), which developed in a solifluidal redeposited (MIS 5d) interglacial Cambisol (MIS 5e). Cryosols, typical for MIS 6 sequences, are present in the loess sediment below. The lower pedocomplex formed during several warm stages of varying intensities, with interruptions caused by colluvial processes and admixture of eolian sediment during colder stages.
15001604 Woronko, Barbara (University of Warsaw, Department of Geography and Regional Studies, Warsaw, Poland); Rychel, Joanna; Karasiewicz, Miroslaw T.; Ber, Andrzej; Krzywicki, Tomasz; Marks, Leszek and Pochocka-Szwarc, Katarzyna. Heavy and light minerals as a tool for reconstructing depositional environments; an example from the Jalowka site (northern Podlasie region, NE Poland): in Heavy-mineral analysis as a tool in earth-scientific research (van Loon, A. J. Tom, editor), Geologos (Wroclaw), 19(1-2), p. 47-66, illus., 90 ref., 2013.
Part of northern Podlasie (NE Poland), shaped during the Wartanian stadial of the Odranian glaciation (Saalian), was situated in the periglacial zone during the Vistulian (Weichselian) glaciation. Both landforms and sediments were affected by the periglacial conditions. This is recorded at the Jalowka site, at the floor of a dry valley, where mineral deposits of 4.13 m thick, overlying organic deposits from the Eemian interglacial, were examined. These mineral deposits form four units, from bottom to top: a fluvial unit (I), a loess-like unit (II), a solifluction unit (III), and an aeolian unit with ice wedges (IV) on top of unit III. The heavy and light minerals were analysed, as well as the geochemistry, in order to find out about the parent material and to reconstruct the climatic conditions during deposition. The mineral analysis indicates that the Saalian till was predominantly derived from shallow-marine deposits; erosion accompanied by sorting of the heavy minerals took place on the basis of their mass and grain size. The original material of the till seems therefore to be sedimentary rocks from the eastern Central Baltic Basin. This material became strongly weathered under the periglacial conditions, resulting in the destruction of the quartz grains, as well as in leaching, leading to complete decalcification of the deposits. Aeolian activity resulted in infilling of ice wedges and the creation of thin layers. The intensity and the duration of these processes was limited, so that the effects of the aeolian abrasion are insignificant. Neither resulted the aeolian activity in significant reshaping of the landscape.
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15009635 Damm, Bodo (University of Vechta, Vechta, Germany) and Felderer, Astrid. Impact of atmospheric warming on permafrost degradation and debris flow initiation; a case study from the Eastern European Alps: in Environment, man, geohazards in the Quaternary (Zöller, Ludwig, editor), Eiszeitalter und Gegenwart - Quarternary Science Journal, 62(2), p. 136-149 (German sum.), 75 ref., 2013. Meeting: 36th assembly of the German Quaternary Association, Sept. 16-20, 2012, Bayreuth, Germany.
The present study demonstrates the importance of recent atmospheric warming for the spatial distribution of debris flow initiation in a central alpine area of the Eastern Alps. In particular, permafrost degradation due to increasing mean annual air temperature (MAAT) since the end of the Little Ice Age (LIA) caused mechanical instabilities of sediments and slopes. In the study area, the Rieserferner-Ahrn Nature Park, it can be shown that almost half of the debris flow initiation zones originate in areas with loose rock that were still stabilized by glacier ice and/or permafrost about 150 years ago.
15001535 Coppa, Zachary J. (Delaware Geological Survey, Newark, DE); Andres, A. Scott; He, Changming and McKenna, Thomas E. Delaware Groundwater Monitoring Network; geochemical analyses supporting sustainable resource management [abstr.]: in Geological Society of America, Southeastern Section, 63rd annual meeting, Abstracts with Programs - Geological Society of America, 46(3), p. 16, 2014. Meeting: Geological Society of America, Southeastern Section, 63rd annual meeting, April 10-11, 2014, Blacksburg, VA.
The Delaware Groundwater Monitoring Network has collected detailed hydrogeologic information from new wells constructed in confined aquifers (Rancocas, Mt. Laurel, and Magothy) that address near-term critical water resource management issues in southern New Castle and northern Kent Counties. The results of this research will improve our predictive capabilities of how changes in environmental conditions and a growing population will affect future water availability. Groundwater 18O and 2H values indicate a colder recharge temperature, correlating to an age of approximately 15,000 years old. In comparison, concurrently collected samples yield conventional 14C ages of 6,500 - 16,200 years old. The 18O and 2H values plot below the Global Meteoric Water Line, indicating slight evaporative affects prior to infiltration and potentially smaller paleo-recharge areas. Areas and rates of recharge were reduced due to the presence of discontinuous permafrost. 18O-enriched values correlate with elevated total dissolved solids (TDS) caused by pumping-induced saltwater intrusion or the dissolution of Na (smectite and feldspar group clays) and Cl (chloride) via the percolation of meteoric water through the subsurface. The model indicates that the Magothy aquifer has elevated salinity values due to pumping-induced landward flow beneath the Delaware Bay. TDS does not increase along flow paths determined by a flow-model particle track simulation of the Mount Laurel and Magothy aquifers, even though shallow upgradient aquifer units are composed of resistant quartz sand and more soluble calcite- and glauconite-rich sands are present downgradient. Rather, local hydrogeologic factors and leaching of agricultural contaminants run-off upgradient cause elevated TDS in shallow portions of flow paths. TDS within the Rancocas aquifer appears to increase with increasing flow distance; however, the R2-value is not significant. TDS increases with decreasing elevation indicating that relative groundwater age can be determined from TDS values.
15009479 Osman, Matthew (Augustana College, Geology Department, Rock Island, IL); Varner, Ruth; Palace, Michael; Wik, Martin; Lang, Ashley and Crill, Patrick. Employing passive acoustics as a temporally precise monologue for constraining ebullitive methane fluxes in warming subarctic lakes [abstr.]: in Geological Society of America, North-Central Section, 48th annual meeting, Abstracts with Programs - Geological Society of America, 46(4), p. 10, 2014. Meeting: Geological Society of America, North-Central Section, 48th annual meeting, April 24-25, 2014, Lincoln, NE.
Systematic difficulties in capturing the large spatial and temporal variability of ebullition (bubbling) has promoted a broad range of uncertainty in our understanding of the role of lakes as key emitters of atmospheric methane (CH4). With the projected warming and ongoing thawing of high-latitude frozen peatlands abundant in small lakes and ponds, there is an increasing need for methods that provide high-temporal resolution delineating precisely when and under what circumstances ebullitive fluxes occur. Employing the well-established Minnaert resonance formula as a reliable proxy for bubble volume, we designed a system of passive acoustic hydrophone sensors calibrated to continuously record ebullition from lakes at 160 kbits/sec. We present here the results of three summer field seasons (2011-2013) of acoustic and manual bubble flux measurements from four subarctic lakes situated in discontinuous permafrost regions of northern Sweden and Alaska. Results show trends similar to prior lake measurements in the subarctic. We found wide variation in CH4 concentrations, spanning between 0.10 to 95.16%. Fluxes ranged from 0-279.72 mg CH4 m-2 d-1 and averaged 12.03 mg CH4 m-2 d-1 (n=401) over the three-year period. High-resolution time series analysis of our measurements will be compared alongside standard meteorological parameters such as atmospheric pressure, temperature, rainfall, water table, wind speed, and radiative inputs to infer dominant external forcings on ebullition. Radiocarbon and 13C/12C ratios of bubble samples collected from Swedish lakes in July 2013 are to be subsequently analyzed for age, transport and production mechanisms.
15002175 Narantsetseg, Ts. (Mongolian Academy of Sciences, Institute of Geology and Mineral Resources, Ulaanbaatar, Mongolia); Krivonogov, S. K.; Oyunchimeg, Ts.; Uugantsetseg, B.; Burr, G. S.; Tomurhuu, D. and Dolgorsuren, Kh. Late glacial to middle Holocene climate and environmental changes as recorded in Lake Dood sediments, Darhad Basin, northern Mongolia: in Hydrological and ecological responses to climatic change and to land-use/land-cover changes in Central Asia (Feng Zhaodong, editor), Quaternary International, 311, p. 12-24, illus. incl. sects., 4 tables, sketch map, 74 ref., October 17, 2013. Meeting: International conference on Hydrological and ecological responses to climatic change and to land use/land-cover changes in Central Asia, Aug. 6-9, 2012, Urumqi, China.
The paper presents new data on climatic, lake level and environmental changes in the Darhad Basin, northern Mongolia, during the Late Glacial and Early to Middle Holocene. Two cores, DN1 and DN2, from Lake Dood were investigated using the following proxies: grain size, total carbon (TC), total inorganic carbon (TIC), total organic carbon (TOC), total nitrogen (TN), total sulfur (TS), d13C, d18O and diatom. Our reconstructions indicate that dramatic climatic and environmental changes occurred several times since ca 14 ka cal BP. A cold and dry climate of the Late Glacial changed to a relatively cold and wet climate starting around 9.5 ka cal BP in response to an Early Holocene humidization. A generally warm and humid climate prevailed in the region at ca. 7.8-5.8 ka cal BP. Later on after 5.8 ka cal BP the climate became cooler and drier. The Darhad paleolake, the predecessor of Lake Dood, disappeared during the Late Glacial to Early Holocene times and started to reappear since ca. 9.5 ka cal BP. Lake Dood fluctuated considerably in response to changes in precipitation or/and in ground ice melting between 9.5 and 5.8 ka cal BP and started to decrease at 5.8 ka cal BP. Abstract Copyright (2013) Elsevier, B.V.
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