Mineralogical, geochemical, magnetic, and siliciclastic grain‐size signatures of 34 surface sediment samples from the Mackenzie‐Beaufort Sea Slope and Amundsen Gulf were studied in order to better constrain the redox status, detrital particle provenance, and sediment dynamics in the western Canadian Arctic. Redox‐sensitive elements (Mn, Fe, V, Cr, Zn) indicate that modern sedimentary deposition within the Mackenzie‐Beaufort Sea Slope and Amundsen Gulf took place under oxic bottom‐water conditions, with more turbulent mixing conditions and thus a well‐oxygenated water column prevailing within the Amundsen Gulf. The analytical data obtained, combined with multivariate statistical (notably, principal component and fuzzy c‐means clustering analyses) and spatial analyses, allowed the division of the study area into four provinces with distinct sedimentary compositions: (1) the Mackenzie Trough‐Canadian Beaufort Shelf with high phyllosilicate‐Fe oxide‐magnetite and Al‐K‐Ti‐Fe‐Cr‐V‐Zn‐P contents; (2) Southwestern Banks Island, characterized by high dolomite‐K‐feldspar and Ca‐Mg‐LOI contents; (3) the Central Amundsen Gulf, a transitional zone typified by intermediate phyllosilicate‐magnetite‐K‐feldspar‐dolomite and Al‐K‐Ti‐Fe‐Mn‐V‐Zn‐Sr‐Ca‐Mg‐LOI contents; and (4) mud volcanoes on the Canadian Beaufort Shelf distinguished by poorly sorted coarse‐silt with high quartz‐plagioclase‐authigenic carbonate and Si‐Zr contents, as well as high magnetic susceptibility. Our results also confirm that the present‐day sedimentary dynamics on the Canadian Beaufort Shelf is mainly controlled by sediment supply from the Mackenzie River. Overall, these insights provide a basis for future studies using mineralogical, geochemical, and magnetic signatures of Canadian Arctic sediments in order to reconstruct past variations in sediment inputs and transport pathways related to late Quaternary climate and oceanographic changes.

The deep biosphere is the largest microbial habitat on Earth and features abundant bacterial endospores. Whereas dormancy and survival at theoretical energy minima are hallmarks of microbial physiology in the subsurface, ecological processes such as dispersal and selection in the deep biosphere remain poorly understood. We investigated the biogeography of dispersing bacteria in the deep sea where upward hydrocarbon seepage was confirmed by acoustic imagery and geochemistry. Thermophilic endospores in the permanently cold seabed correlated with underlying seep conduits reveal geofluid-facilitated cell migration pathways originating in deep petroleum-bearing sediments. Endospore genomes highlight adaptations to life in anoxic petroleum systems and bear close resemblance to oil reservoir microbiomes globally. Upon transport out of the subsurface, viable thermophilic endospores reenter the geosphere by sediment burial, enabling germination and environmental selection at depth where new petroleum systems establish. This microbial dispersal loop circulates living biomass in and out of the deep biosphere.

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The Laurentide Ice Sheet (LIS) covered most of North America during the last glaciation and the 29 eastern margin of Baffin Island, in the eastern Canadian Arctic, has been shaped by its phases of 30 advance and retreat (Dyke & Prest 1987; Dyke 2004). Therefore, Baffin Bay, located between 31 Baffin Island and Greenland, forms a unique setting capturing sediments related to the pulses of 32 ice sheet margins on the surrounding continental shelves (e.g.

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This study presents the first detailed description of the upper sedimentary succession of the late Pleistocene and Holocene deposits in the Gulf of San Jorge (Patagonia) based on several hundred kilometers of high‐resolution seismic (sparker) profiles and numerous sediment cores. High‐resolution seismic stratigraphy confirms the existence of a paleo‐fluvial network formed during sea‐level lowstands and buried by central basin estuarine deposits during the last marine transgression. Analyses of lithostratigraphy and radiocarbon ages indicate the onset of subtidal sedimentation at ~14 cal ka bp. Before the onset of subtidal conditions, the first steps of marine incursion seem to have led to the development of lagoonal/wind–tidal flat environments, advocating for a sea‐level stillstand. An abrupt increase in the log(Ti/Ca) ratio in a distinct multi‐centimeter‐thick layer and the identification of a wave‐ravinement surface suggest rapid sea‐level rise in the gulf prior to ~14 cal ka bp, consistent with Meltwater Pulse 1A. Overall, this study highlights the significant impact of sea‐level rise on sedimentation in the gulf from the onset of marine incursions to the mid‐Holocene, as well as the reduced contribution, as currently observed, of riverine inputs due to the progressive diminution and withdrawal of glacial drainage starting before the Holocene.

The deep biosphere is the largest microbial habitat on Earth and features abundant bacterial endospores1,2. Whereas dormancy and survival at theoretical energy minima are hallmarks of subsurface microbial populations3, the roles of fundamental ecological processes like dispersal and selection in these environments are poorly understood4. Here we combine geophysics, geochemistry, microbiology and genomics to investigate biogeography in the subsurface, focusing on bacterial endospores in a deep-sea setting characterized by thermogenic hydrocarbon seepage. Thermophilic endospores in permanently cold seabed sediments above petroleum seep conduits were correlated with the presence of hydrocarbons, revealing geofluid-facilitated cell migration pathways originating in deep oil reservoirs. Genomes of thermophilic bacteria highlight adaptations to life in anoxic petroleum systems and reveal that these dormant populations are closely related to oil reservoir microbiomes from around the world. After transport out of the subsurface and into the deep-sea, thermophilic endospores re-enter the geosphere by sedimentation. Viable thermophilic endospores spanning the top several metres of the seabed correspond with total endospore counts that are similar to or exceed the global average. Burial of dormant cells enables their environmental selection in sedimentary formations where new petroleum systems establish, completing a geological microbial loop that circulates living biomass in and out of the deep biosphere.

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