Late Pleistocene yedoma in south-western Yukon (Canada): a remnant of Eastern Beringia?

Yedoma deposits developed from the syngenetic accumulation and freezing of organic-rich and ice-rich sediments during the Late Pleistocene over vast portions of Siberia, Alaska and Yukon Territory. Cryostratigraphic investigations revealed the presence of a yedoma deposit in the Beaver Creek area of south-western Yukon. The Beaver Creek area was not glaciated during the last glacial advance and the cryostratigraphic record comprises Middle Wisconsinian up to Holocene deposits covering the Mirror Creek disintegration moraine. Reworking of glacial deposits by alluvial and solifluction processes and peat accumulation in the depression of the hummocky moraine likely occurred during the Middle Wisconsinian period and was followed during the Late Wisconsinian by the yedoma build-up. A major thaw event interrupted the syngenetic permafrost aggradation which eventually resumed as attested by the upward growth of ice wedges

Landscape-related ground ice variability on the Yukon coastal plain inferred from computed tomography and remote sensing

Warming in the Arctic causes strong environmental changes with degradation of permafrost (permanently frozen ground). Active layer deepening (gradual thaw) and permafrost erosion (abrupt thaw) results in the mobilization and lateral transport of organic carbon, altering current carbon cycling in the Arctic. Ground ice content is a crucial factor limiting our understanding and ability to determine the rates and dynamics of permafrost thaw and its impact on potential thaw subsidence rates, changes in lateral hydrological pathways and its driving mechanisms on a landscape scale. In this study we investigate ground ice content and its characteristics across the most dominant landscape units of the Yukon coastal plain (Canadian Arctic), using two spatially and technically contrasting approaches. In our bottom-up approach, twelve permafrost cores were collected from moraine, lacustrine, fluvial and glaciofluvial deposits using a SIPRE corer (mean drilling depth of 2 m) in spring of 2019. Ground ice and sediment contents within polygon centers were analyzed and classified using computed tomography and image recognition software (k-means). Our top-down approach quantified ice-wedge volumes from remote sensing imagery tracing the circumference of polygon troughs over the same area. Preliminary results - extrapolated to the entire coastal plain - show that the ground-ice content in polygon centers vary significantly from massive ice in the polygon troughs (wedge-ice). Total ice volume was estimated around 80.2 vol.-%, of which 68.2 ± 18.1 vol.-% was attributed to ground ice in polygon centers, and 12 ± 3.1 vol.-% of the landscape is massive ice in wedge-ice along polygon troughs. Additionally, differences among and between landscape units are also substantial, with highest ice volume contents in moraines landscapes, where polygon centers contain 58.8 vol.-% ground ice and wedge-ice volume is 16.2 vol.-%), while the lowest ice contents are found in glacio-fluvial deposits (22.1 vol.-% resp. 9.1 vol.-%). Our results reveal a higher average and a larger variability in ground ice contents than previously found, suggesting a need of both ground-based measurements and remote sensing imagery to further our understanding of the future landscape subsidence, but also to avoid a likely under- or overestimation associated with the chosen approach. We conclude that due to the high ground ice contents on the Yukon coastal plain, substantial changes of the permafrost landscape will occur under current warming trends. These will include subsidence, abrupt erosion, changes in hydrology and organic carbon mobilization, degradation and export processes, which will differ between landscape units

Genèse et structure du pergélisol (étude de formes périglaciaires de soulèvement au gel au Nunavik (Québec nordique), Canada)

CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

The potential lateral growth of lithalsas

The lithalsas in the Hudson Bay region of northern Québec, Canada, are the closest modern analogs of ancient features that collapsed to form conspicuous circular depressions ("viviers") common in the Hautes-Fagnes, a region in Belgium. Observations made in both regions are complementary and suggest that these mounds formed by frost heaving displacing soil not only upward, as previously assumed, but also laterally. This lateral displacement is consistent with diverse observations and inferences, which include (1) the simple rounded outline, either circular or oval, typical of both active and relic lithalsas; (2) evidence of local lateral extension inferred from exposures of the relic forms; (3) the relative inefficiency of solifluction in accumulating surface material to form the peripheral ramparts of remnant lithalsas due to the very gentle slopes of the mounds; and (4) the dip of ice lenses within a lithalsa in the Hudson Bay region, perhaps indicating that the freezing front dipped outward along its periphery. The growth of segregation ice is the primary driver for the vertical growth and lateral enlargement of a lithalsa. © 2011 University of Washington

Molar gas ratios and stable oxygen and nitrogen isotopes of air entrapped in ice, North America

The molar ratios of atmospheric gases change during dissolution in water due to differences in their relative solubilities. We exploited this characteristic to develop a tool to clarify the origin of ice formations in permafrost regions. Extracted from ice, molar gas ratios can distinguish buried glacier ice from intrasedimental ground ice formed by freezing groundwaters. An extraction line was built to isolate gases from ice by melting and trapping with liquid He, followed by analysis of N2, O2, Ar, 18O-O2 and 15N-N2, by continuous flow mass spectrometry. The method was tested using glacier ice, aufeis ice (river icing) and intrasedimental ground ice from sites in the Canadian Arctic. O2/Ar and N2/Ar ratios clearly distinguish between atmospheric gas in glacial ice and gases from intrasedimental ground ice, which are exsolved from freezing water. 615NN2 and 618OO2 in glacier ice, aufeis ice and intrasedimental ground ice do not show clear distinguishing trends as they are affected by various physical processes during formation such as gravitational settling, excess air addition, mixing with snow pack, and respiration

Investigation of a novel series of 2-hydroxyisoquinoline-1,3(2H,4H)-diones as human immunodeficiency virus type 1 integrase inhibitors

We report herein further insight into the biological activities displayed by a series of 2-hydroxyisoquinoline-1,3(2H,4H)-diones (HIDs). Substitution of the N-hydroxyimide two-metal binding pharmacophore at position 4 by carboxamido side chains was previously shown by us to be fruitful for this scaffold, since strong human immunodeficiency virus type 1 integrase (HIV-1 IN) inhibitors in the low nanomolar range associated with low micromolar anti-HIV activities were obtained. We investigated the influence of substitution at position 7 on biological activity. Introduction of electron-withdrawing functional groups such as the nitro moiety at position 7 led to a noticeable improvement of antiviral activity, down to low nanomolar anti-HIV potencies, with advantageous therapeutic indexes going close to those of the clinically used raltegravir and retained potencies against a panel of IN mutants.status: publishe

Investigation of a novel series of 2-hydroxyisoquinoline-1,3(2H,4H)-diones as human immunodeficiency virus type 1 integrase inhibitors.

International audienceWe report herein further insight into the biological activities displayed by a series of 2-hydroxyisoquinoline-1,3(2H,4H)-diones (HIDs). Substitution of the N-hydroxyimide two-metal binding pharmacophore at position 4 by carboxamido side chains was previously shown by us to be fruitful for this scaffold, since strong human immunodeficiency virus type 1 integrase (HIV-1 IN) inhibitors in the low nanomolar range associated with low micromolar anti-HIV activities were obtained. We investigated the influence of substitution at position 7 on biological activity. Introduction of electron-withdrawing functional groups such as the nitro moiety at position 7 led to a noticeable improvement of antiviral activity, down to low nanomolar anti-HIV potencies, with advantageous therapeutic indexes going close to those of the clinically used raltegravir and retained potencies against a panel of IN mutants

ACS Med Chem Lett

A series of 2-hydroxy-1,3-dioxoisoquinoline-4-carboxamides featuring an N-hydroxyimide chelating functionality was evaluated for their inhibitory properties against human immunodeficiency virus type 1 integrase (HIV-1 IN). Several derivatives displayed low nanomolar IC50 values comparable to that of the clinically used raltegravir. A marked effect of one compound on both primary IN-catalyzed reactions, strand transfer (ST), and 3' processing (3'-P), emphasizes a novel IN inhibition mechanism establishing it as a potential new generation IN inhibitor. Substitution of the 2-hydroxyisoquinoline-1,3-dione scaffold at position 4 by carboxamido chains was beneficial for antiviral activity since reproducible low micromolar anti-HIV activities were obtained for the first time within this scaffold