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In an attempt to determine to what extent the impact of recent climate changes that occurred east of Hudson Bay, including important reduction of areas in permafrost, had on the coastal marine environment, a series of shallow cores were extracted from the seabed off the mouth of the Sheldrake River, in Nastapoka Sound. A total of 25 cores were taken in April 2009 from the ice cover. A preliminary seafloor map was first done to help in the selection of the coring sites. Nastapoka Sound has a complex subaqueous relief, formed of asymmetric ridges and deep basins. After preliminary sedimentological analyses, six of the cores were selected for physical and chronological analyses ([sup.14]C, [sup.210]Pb, and [sup.137]Cs dating); among them, three were selected for elemental (C, N, OC/TN) and isotopic (δ[sup.13]C, δ[sup.15]N) analyses to identify sedimentary organic matter sources. Sedimentation processes are complex and are primarily driven by bottom currents. This is confirmed by the absence of a clay fraction in several cores, some erosion surfaces in a few cores, and the presence of comet-like mark features on the seafloor. The highest sedimentation rates are found near the coast of the province of Quebec and Gillies Island and the lowest ones occur in the deep depocenters. Isotopic and elemental analyses reveal that Nastapoka Sound is an area of mixing between marine and terrestrial inputs and can be compared to an estuarine system similar to nearby Lac Guillaume-Delisle. Those conditions altogether make it difficult to extract a perfectly clear signal of climate change in the recent sediment record. However, the downcore application of a simple two end-member mixing model to measured δ[sup.13]C values strongly suggests that the fraction of sedimentary organic matter from terrestrial sources increased by 30% since about the middle of the Little Ice Age. This trend accelerated at the end of the 20th century. Rapid permafrost decay in adjacent river catchments is likely one source for this terrestrial carbon. However, it cannot be distinguished from other potential sources that are also related to environmental changes such as increase in primary productivity both on land, where peatlands, shrubs, and forest are expanding, and at sea, where sea ice cover duration is diminishing. Dans le but de determiner l'etendue des impacts des changements climatiques recents qui ont eu lieu a l'est de la baie d'Hudson, incluant une reduction significative des secteurs de pergelisol, sur l'environnement marin cotier, une serie de carottes peu profondes a ete prelevee du lit marin a l'embouchure de la riviere Sheldrake, dans le detroit de Nastapoka. Un total de 25 carottes a ete preleve a partir de la couverture glaciaire en avril 2009. Une carte preliminaire du plancher oceanique a ete dressee afin d'aider a choisir les sites de prelevement des carottes. Le detroit de Nastapoka a un relief subaquatique complexe, forme de cretes asymetriques et de bassins profonds. Apres des analyses sedimentologiques preliminaires, six carottes ont ete choisies pour des analyses physiques et chronologiques (datation par [sup.14]C, [sup.210]Pb et [sup.137]Cs; parmi celles-ci, trois ont finalement ete selectionnees pour des analyses elementaires (C, N, C/N (carbone organique / azote total)) et isotopiques (δ[sup.13]C, δ[sup.15]N) afin d'identifier les sources de matieres organiques sedimentaires. Les processus de sedimentation sont complexes et fortement influences par les courants de fond. Cela est confirme par l'absence d'une fraction argileuse dans plusieurs carottes, des surfaces d'erosion dans quelques carottes et la presence de marques de style comete sur le fond de l'ocean. Les taux de sedimentation les plus eleves se trouvent a proximite de la cote de la province de Quebec et de l'ile Gillies et les taux les plus faibles se trouvent dans les endroits de deposition les plus profonds. Les analyses isotopiques et elementaires montrent que le detroit de Nastapoka est un endroit de melange entre les intrants marins et terrestres et qu'il peut etre compare a un systeme estuarien semblable a celui du Lac Guillaume-Delisle a proximite. Prises ensemble, ces conditions peuvent rendre difficile l'extraction d'un signe parfaitement clair de changement climatique dans le profil stratigraphique recent. Toutefois, l'application, au bas de la carotte, d'un modele simple de melange de deux extremites, aux valeurs δ[sup.13]C mesurees suggere fortement que la fraction de matiere organique sedimentaire provenant de sources terrestres s'est accrue de 30 % depuis environ le milieu du Petit Age glaciaire. Cette tendance s'est acceleree a la fin du 20e siecle. Le declin rapide du pergelisol dans des bassins hydrographiques adjacents constitue probablement une des sources de ce carbone terrestre. Toutefois, il ne peut pas etre distingue d'autres sources potentielles qui sont aussi reliees a des changements environnementaux tels qu'une augmentation de productivite primaire a la fois sur terre, ou s'etendent les tourbieres, les arbustes et les forets, et en mer ou la duree de la couverture de glace diminue. [Traduit par la Redaction], Introduction The Hudson Bay bottom sediments are of interest because they contain a record of the environmental changes that took place in the terrestrial environment of its surrounding catchment. Starting [...]

Abstract: Lac Guillaume-Delisle Estuary and Nastapoka Sound are two sedimentary basins that recorded the late Quaternary deglaciation on the eastern coast of Hudson Bay. Acoustic profiles reveal an average sediments [...]

Abstract: A systematic approach was used for the interpretation of the electrical resistivity tomography carried out on two permafrost mounds at Umiujaq in Nunavik, Canada, to assess their internal structure [...]

Abstract: This study presents new knowledge about the ice segregation and frost-heave processes taking place in a typical lithalsa. A tomodensitometric scanner was used to produce high-resolution computer images of [...]

We evaluated the spatial distribution and morphological variability of thermal contraction crack polygon (TCCP) networks across Nunavik, a 440,000‐km2 region of northern Québec that spans the northward transition from discontinuous to continuous permafrost. A population of 4,567 TCCP sites was sampled and analyzed from 80,737 georeferenced high‐resolution aerial photographs and 264,504 km2 of ESRI satellite basemaps. For each site, six parameters were inventoried and compiled into a database: (a) network geometric arrangement; (b) intersection angles; (c) number of subdivisions and nested polygons (referred to as generations of development); (d) dominant polygon morphology; (e) surficial geology; and (f) vegetation cover. Statistical analyses of the tabulated data revealed a strong association between Holocene glacial, glacio‐fluvial, fluvial, marine, and organic landforms and the different intersections angles in the networks, providing insight into how the processes of thermal contraction cracking function and manifest geomorphically across varied permafrost landscapes. Orthogonal polygons (intersection angle of 90°) dominate on flat terrains where the thermo‐mechanical stresses are probably spatially homogeneous. Hexagonal (angles of 120°) and poorly structured polygons tend to form where topography variability probably generates heterogeneous heat flow patterns and thermo‐mechanical stresses in the ground, resulting in irregular cracking patterns. [ABSTRACT FROM AUTHOR]