High‐resolution swath bathymetry data collected in fjord‐lakes Pentecôte, Walker and Pasteur (eastern Québec, Canada) allowed imaging in great detail the deltas of four rivers in order to understand ...the factors controlling the formation and downslope evolution of bedforms present on their slopes. The morphometry and morphology of 199 bedforms reflect the behaviour of sediment density flows. The shape of the bedforms, mostly crescentic, and the relationships between their morphological properties indicate that they were formed by supercritical density flows and that they are cyclic steps. The crescentic shape suggests an upslope migration while the aspect ratios and increasing wavelengths with distance from the shore (and decreasing slopes) are compatible with a cyclic step origin. At the rollover point, the acceleration of the density flows on steep slopes produces tightly spaced hydraulic jumps and favours short wavelength and symmetrical bedforms. Further downslope, decreasing slopes and increasing specific discharge increase the wavelength and asymmetry of the bedforms. The wavelength and asymmetry are increased because density flows require longer distances to become supercritical again on lower slopes after each successive hydraulic jump. Bedform morphometry and morphology are used to reconstruct density flow behaviour downslope. Froude numbers are high near the rollover point and gradually decrease downslope as the slope becomes gentler. Conversely, the specific discharge and flow depth are low near the rollover point and gradually increase downslope as the flow either erodes sediments or becomes more dilute due to sediment deposition and water entrainment. The supercritical density flows are believed to be triggered mainly by hyperpycnal flows but some evidence of delta‐front slope failures is also observed. The differences in delta morphology and bedform development between the four deltas are linked to basin morphology and watershed hydrology, but also mainly to the fjord heritage of the lakes that allowed the focusing of sediment at the delta front.
This paper presents a series of 50 geomorphological maps of the seabed of northeastern Baffin Island fiords and cross-shelf troughs, in eastern Arctic Canada. The mapping was produced using swath ...bathymetry imagery from multiple bathymetry datasets. A total of 24 types of landform were systematically mapped (>55,000 landforms) and reflect processes linked to subglacial, ice-marginal or paraglacial to postglacial environments. The landforms record the transition of the seabed from being covered by a marine-terminating ice sheet to the establishment of postglacial conditions. The landform assemblages allow the distinction of ice-flows orientation and ice-stream pathways along fiords and cross-shelf troughs. The multiple moraines and grounding-zone wedges indicate that the ice margin stabilized during retreat and that the overall deglaciation occurred by steps. These maps provide a framework for future investigations in northeastern Baffin Island fiords and shelf and can also provide a template for future seabed geomorphological studies in Arctic Canada.
Over the past decades, riparian land-use changes coupled to the multiplication of river infrastructures have enhanced vulnerability issues for societies and ecosystems located along large rivers. ...Exposure to geohazards is also changing due to the ongoing climate change, underlining the need for flexible management strategies for riparian environments. In this perspective, GIS-based mapping allows integrating a wide range of environmental data. However, such datasets are often incomplete and not homogeneous over large geographical scales, which can be problematic for the implementation of regional land-use planning strategies. Using the St. Lawrence fluvial system (SLFS) (Québec, Canada) as a case study, this article reports and describes a high-resolution approach to map position, characteristics and erosion susceptibility of natural and artificial riverbanks from a combination of field-based, remote sensing and local knowledge-derived data. This approach allowed identifying erosion-prone sites and highlighting dominant erosion processes and spatially constrain them along the SLFS. The proposed geospatial framework constitutes (1) an initial portrait of the riverscape that will allow an effective implementation of future monitoring and process-based studies; and (2) a first step in supporting land-use planning stakeholders in the selection of appropriate measures to ensure a greater resilience of riparian communities and ecosystems.
The Magdalen Islands (Québec, Canada) in the centre of the Gulf of St. Lawrence are located in a strategic position for providing an overview of the relative sea-level (RSL) history of the Maritime ...Provinces of eastern Canada. Although data are available for the coastal terrestrial areas of the Maritimes, data from the Gulf are very scarce and both the RSL and glacio-isostatic adjustment (GIA) models extrapolate for this central region. This study provides new stratigraphic and chronological data from four outcrops and two coring sites on the Magdalen Islands. In addition to the five samples used mainly for age control purposes, nine new luminescence ages are presented. With these new data added to the available literature, a new RSL curve is reconstructed for the LGM to the late Holocene period and a partial curve is proposed for the interval between the late MIS 4 to the MIS 3. Data also indicate a few insights for the MIS 5 period. Results reveal that for the LGM to the late Holocene, the curve corresponds to the J-shaped curve scenario recognized in the literature. The RSL changes during this period are the result of glacio-isostatic rebound, migration and collapse of the peripheral forebulge, and eustatic sea-level changes. For the LGM to the early Holocene, glacio-isostatic depression curves displaying a few local differences are also proposed. For the late Holocene, the data constrain the curve between two types of indicators, i.e. marine and terrestrial, and indicate that the RSL has risen at least 3 m during the last two millennia. Sediments dated to the MIS 5 and the interval between the late MIS 4 and the MIS 3 illustrate that the GIA following the LGM also occurred for the MIS 5 interglacial and the MIS 3 interstadial. Finally, recent GIA models are discussed in light of the results of this paper.
•Relative sea-level (RSL) curves from late MIS 4 to Holocene are proposed.•The post-LGM RSL scenario for the Magdalen Islands follows a J-shaped type curve.•Glacio-isostatic depression curves from LGM to Holocene are suggested.•Local differences in crustal depression are due to distinct glacial histories.
Abstract
The glaciological significance of ice shelves is relatively well established for the stability of modern ice sheets of Antarctica. Past ice shelves of the Arctic, however, are poorly ...documented while their role for the stability of former ice sheets remains mostly unknown. Here we present swath bathymetry data and seismostratigraphic profiles that reveal a large moraine system extending along the continental slope off Baffin Island, demonstrating that a 500-m thick ice shelf covered northern Baffin Bay during the last glacial episode. We suggest that this ice shelf had a profound impact on the stability of a series of major ice streams that drained the interior of the Laurentide, Innuitian and Greenland ice sheets. Climate warming and global sea-level rise in the early stage of deglaciation possibly contributed to a large-scale break-up of the ice shelf, which led to the destabilisation and reorganisation of tributary ice streams from these three ice sheets.
Fiord morphology plays a fundamental role in glacier flow dynamics and on ice-margin stability. As most of the present-day margins of the Greenland Ice Sheet lays in fiords, there is a need for ...understanding short- and long-term glacial dynamics in fiord settings. We investigate ice-sheet retreat patterns in previously glaciated submarine terrain of northeastern Baffin Island fiords to provide analogues for modern and future ice-sheet response to climate change and sea-level rise. Geomorphological maps constructed from the interpretation of swath bathymetry imagery in fiords of northeastern Baffin Island reveal a wide range of glacial to postglacial landforms that allow the reconstruction of past ice-sheet retreat dynamics. Ice-flow landforms such as mega-scale glacial lineations, crag-and-tails, and meltwater channels reveal the direction and behaviour of late-Foxe ice flow through the fiords. The presence of undisturbed elongated landforms within the fiords suggests that ice streams have probably been active until the late stage of deglaciation. Landforms transverse to ice-flow direction include grounding-zone wedges, frontal moraines, grounding-line fans, recessional moraines and De Geer moraines. These landforms are interpreted as the result of former standstills of the ice margin during deglaciation. The occurrence of grounding zones in deep (>800 m) part of the fiords contrasts with studies suggesting instability and rapid retreat of outlet glaciers over deep fiord basins. Sediment-filled basins, often characterised by the presence of turbidity channels, gullies and mass movement scars occur in-between the moraines. Sediment-filled basins with a ponded architecture between sills illustrate that most of the sediment accumulation was ice-proximal during deglaciation and characterised by gravity-driven flows. The proposed landform-assemblage model for northeastern Baffin fiords includes landforms typical of different fiord landsystems.
•We present high-resolution swath bathymetry imagery from fiords of northeastern Baffin Island.•Ice-flow landforms reveal patterns of fast-flowing outlet glaciers (ice streams).•Glaciers stabilised at great depths and on reverse-bed slopes.•Ice-proximal sedimentation was driven by gravity flows.•We present a typical landform assemblage for the fiords of Baffin Island.
Reconstructing the extent, flow and decay of the Laurentide Ice Sheet (LIS) on the continental shelves of North America during the last glaciation provides paleoglaciological analogues that are ...essential for understanding and predicting how modern marine-based ice-sheets will respond to future climate change and sea level fluctuations. The geometry of the LIS during Marine isotope stage 2 (MIS-2; 29-14 ka BP) is one key element for ice-sheet modelling. The maximum extent of the LIS during this stage is well constrained for most sectors of the ice sheet, but major uncertainties remain, especially along the continental shelves of Arctic Canada. Despite a series of recent papers, the extent of the LIS in Western Baffin Bay, an area draining large volumes of glacial ice through multiple ice streams and likely characterized by ice shelves, remains highly speculative. Here we present unequivocal marine geophysical evidence that during the MIS-2 the LIS extended to the edge of the continental shelf, seaward of the previously proposed limits and subsequently retreated episodically westward during deglaciation. These data support interpretations of deep glacial ice grounding in Western Baffin Bay.
This Data in Brief article presents sedimentological and geochemical parameters from a set of sedimentary samples collected in the Saint-Charles River, a tributary of the Saint-Lawrence River flowing ...in Québec City (QC, Canada). It details the experimental design, methods, materials and results of destructive analyses related to a multi-proxy study of polymetallic contamination in sediments collected within an urban reservoir (Spatial and temporal patterns of metallic pollution in Québec City, Canada: Sources and hazard assessment from reservoir sediment records, https://doi.org/10.1016/j.scitotenv.2019.04.021, (Chassiot et al., 2019)). The present article summarizes the results of relevant parameters on a set of 68 samples: total organic carbon (TOC), sulfur content, grain-size, and concentrations of heavy and trace metals. It also presents the calculation of enrichment factors, geoaccumulation indexes, and metallic pollution index.
This quantitative reanalysis reviews the high-fidelity record of ice-sheet dynamics and ensuing sediment supply to the greater Lake Melville region of Labrador, Canada. The environment is ...strategically located close to a major ice divide of the Quebec-Labrador Dome (QLD) of the Laurentide Ice Sheet. More than 5000 km of acoustic records are examined along with multibeam bathymetric data acquired over the last 2 decades. Findings reveal a thin (1125 m), low-angle (0.15°–0.21°) ice stream once emanated from the eastern sector of the QLD, which likely over-deepened Cartwright Saddle, a major trough on the Labrador Shelf. Modeled-ice velocities during glaciation are 2500 ± m/yr, allowing the ice sheet to discharge 10,000± icebergs each year into the North Atlantic. The ice stream's flux may have caused a drawdown of the QLD, shifting the ice divide into Lake Melville's drainage basin. After deglaciation began ∼10.4 kyr BP, the ice stream had thinned to ∼820 ± 20 m, reducing ice stream ice velocities to ∼820 ± 50 m/yr. Vertical ablation of the ice sheet proceeded at rates of ∼0.17 m/yr and ice-marginal retreat was on the order of 140 ± m/yr (190 ± m/yr if stillstand pauses are excluded), which resulted in complete deglaciation of the 250 km-long basin in approximately 2500 years. The ice stream delivered, on average, 50 Mt/yr of deglacial sediment between 9 and 8 kyr BP; sediment loads associated with the six largest submarine moraines range 44–64 Mt/yr, delivered by a freshwater discharge 5-fold larger than for modern conditions. With 94 Gt of subglacial and deglacial sediment deposited in Lake Melville, the regional deglacial sediment yield is 300 t/km2/yr, perhaps ∼430 t/m2/yr if terrestrial deglacial deposits are included. Our findings confirm the existence of a Lake Melville ice stream during the Last glacial episode and highlight future research opportunities for empirical and modeling studies directed towards an understanding of ice-sheet dynamics.
•A converging, thin, low-angle ice stream emanated from the eastern sector of the QLD, with flow through Lake Melville.•The ice stream velocity averaged ∼2500 m/yr and discharged ∼10,000 large icebergs each year to the North Atlantic.•The Laurentide Ice Sheet slowed to between 220 m/yr to 820 m/yr, during the 2500-yr period of deglaciation (7.9–10.4 kyr BP).•Subglacial discharge supplied ∼500% more freshwater than for modern conditions and carried a deglacial sediment load of 50 Mt/yr.•The Lake Melville Ice Stream is associated with a sediment yield of between 300 and 430 t/km2/yr.
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